itp120chapt192009binaryinputoutput-091011054706-phpapp01.ppt

7/29/2019 itp120chapt192009binaryinputoutput-091011054706-phpapp01.ppt

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Chapter 19

Binary Input & OutputJava I ITP 120


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ITP 120 Java Programming I2

Patrick Healy

Class #15 Input and OutputChapter Objectives

To understand how I/O is handled in Java

To distinguish between text I/O and binary I/O

To read and write bytes using FileInputStream and FileOutputStream

To read and write primitive values and strings using the DataInputStream and

DataOutputStream classes

To store and restore objects using ObjectOutputStream and ObjectInputStream, and

to understand how objects are serialized and what kind of objects can be serialized

To use the Serializable interface to enable objects to be serializable (optional)

To know how to serialize arrays (optional)

To use RandomAccessFile for both read and write (Optional).


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Patrick Healy

Class #15 Input and Output

Overview

The java.io.*package provides a library of classes to read and writevarious types of data.

In Java, all data I/O is handled in the form of streams

Data streams can be byte streams or character streams

The java.io package has classes that process byte streams of all types

NOTE: In Java, a character is 2 BYTES !

Also NOTE: a Unicode character is 2 bytes !

The Reader and Writer classes process character streams.

Streams can be layered, so that one type of streams can be convertedto another type of streams by chaining. Chaining a character stream

reader to a byte stream reader to read bytes on one end and producecharacters at the other end .


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Patrick Healy


Overview --- Streams

A stream is an abstraction of a continuous one-way flow of data.

Program

Output Stream

File

Input Stream


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Patrick Healy


2 Types of Stream Classes: Bytes & Characters

The stream classes can be categorized into two types: byte streams and

character streams.

The InputStream/OutputStreamclass is the

root of all BYTEstream classes

The Reader/Writer class is the root of all CHARACTERstream

classes.

The subclasses ofInputStream/OutputStreamare analogous to thesubclasses ofReader/Writer.



Patrick Healy


Byte Stream Classes (note: the word stream )

InputStream

OutputStream

RandomAccessFile

Object

PipeOutputStream

SequenceInputStream

StringBufferInputStream

ByteArrayOutputStream

ObjectOutputStream

FilterOutputStream

FileOutputStream

PipedInputStream

PushBackInputStream

BufferedInputStream

LineNumberInputStream

DataInputStream

BufferedOutputStream

DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

ByteArrayInputStreamInputData

OutputData

ObjectOutput

ObjectInput



Patrick Healy

Class #15 Input and OutputCharacter Stream Classes (Character = 2 bytes)

Reader

Writer

StreamTokenizer

Object

PrintWriter

BufferedWriter

CharArrayWriter

PipedWriter

FilterWriter

PipedReader

LineNumberReader

FileReader

PushBackReader

FileWriter

StringWriter

StringReader

InputStreamReader

CharArrayReader

BufferedReader

FilterReader

OutputStreamWriter


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How is I/O Handled in Java?A File object encapsulates the properties of a file or a path, but does not contain

the methods for reading/writing data from/to a file. In order to perform I/O, youneed to create objects using appropriate Java I/O classes.

Formatter output = new Formatter("temp.txt");

output.format("%s", "Java 101");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program

Input object

created from an

input class

Output object

created from an

output class

Input stream

Output stream

File

File010111001

110011011


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Text Files vs. Binary Files Data stored in a text file are represented in human-readable form.

Data stored in a binary file are represented in binary form. You

cannot read binary files. Binary files are designed to be read byprograms. For example, the Java source programs are stored in textfiles and can be read by a text editor, but the Java classes are stored inbinary files and are read by the JVM. The advantage of binary files isthat they are more efficient to process than text files.

Although it is not technically precise and correct, you can imaginethat a text file consists of a sequence of characters and a binary fileconsists of a sequence of bits. For example, the decimal integer 199 isstored as the sequence of three characters: '1', '9', '9' in a text file andthe same integer is stored as a byte-type value C7 in a binary file,because decimal 199 equals to hex C7.


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Binary I/O

Text I/O requires encoding and decoding. The JVM converts a Unicode

to a file specific encoding when writing a character and coverts a filespecific encoding to a Unicode when reading a character. Binary I/O

does not require conversions. When you write a byte to a file, the original

byte is copied into the file. When you read a byte from a file, the exact

byte in the file is returned.

Text I/O program

The Unicode of

the characterEncoding/

Decoding

Binary I/O program

A byte is read/written(b)

(a)

e.g.

"199"

The encoding of the characteris stored in the file

0x31

e.g.

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7

The same byte in the file


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Binary I/O Classes

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


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java.io.InputStream

+read(): int

+read(b: byte[]): int

+read(b: byte[], off: int,

len: int): int

+available(): int

+close(): void

+skip(n: long): long

+markSupported(): boolean

+mark(readlimit: int): void

+reset(): void

Reads the next byte of data from the input stream. The value byte is returned as

an int value in the range 0 to 255. If no byte is available because the end of

the stream has been reached, the value1 is returned.

Reads up to b.length bytes into array b from the input stream and returns the

actual number of bytes read. Returns -1 at the end of the stream.

Reads bytes from the input stream and stores into b[off], b[off+1], ,

b[off+len-1]. The actual number of bytes read is returned. Returns -1 at theend of the stream.

Returns the number of bytes that can be read from the input stream.

Closes this input stream and releases any system resources associated with the

stream.

Skips over and discards n bytes of data from this input stream. The actualnumber of bytes skipped is returned.

Tests if this input stream supports the mark and reset methods.

Marks the current position in this input stream.

Repositions this stream to the position at the time the mark method was last

called on this input stream.

The value returned is a byte as an

int type.

InputStream


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The value is a byte as an int type.

OutputStream

java.io.OutputStream

+write(int b): void

+write(b: byte[]): void

+write(b: byte[], off: int,

len: int): void

+close(): void

+flush(): void

Writes the specified byte to this output stream. The parameter b is an int value.(byte)b is written to the output stream.

Writes all the bytes in array b to the output stream.

Writes b[off], b[off+1], , b[off+len-1] into the output stream.

Closes this input stream and releases any system resources associated with thestream.

Flushes this output stream and forces any buffered output bytes to be written out.


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FileInputStream/FileOutputStream

FileInputStream/FileOutputStream

associates a binary input/outputstream with an external file. All themethods inFileInputStream/FileOuptputStrea

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


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FileInputStream

To construct a FileInputStream, use the following constructors:

public FileInputStream(String filename)

public FileInputStream(File file)

A java.io.FileNotFoundException would occur if you attemptto create a FileInputStream with a nonexistent file.


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FileOutputStream

To construct a FileOutputStream, use the following

constructors:

public FileOutputStream(String filename)

public FileOutputStream(File file)

public FileOutputStream(String filename, boolean append)

public FileOutputStream(File file, boolean append)

If the file does not exist, a new file would be created. If

the file already exists, the first two constructors woulddelete the current contents in the file. To retain thecurrent content and append new data into the file, use thelast two constructors by passing true to the append

TestFileStream Run
http://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestFileStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestFileStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestFileStream.html


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FilterInputStream/FilterOutputStream

Filter streams are streams that filter bytes for some purpose. The basic byte input streamprovides a read method that can only be used for reading bytes. If you want to read integers,

doubles, or strings, you need a filter class to wrap the byte input stream. Using a filter classenables you to read integers, doubles, and strings instead of bytes and characters.FilterInputStream and FilterOutputStream are the base classes for filtering data. When youneed to process primitive numeric types, use DatInputStream and DataOutputStream to filterbytes.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


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DataInputStream/DataOutputStreamDataInputStream reads bytes from the stream andconverts them into appropriate primitive type valuesor strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataOutputStream converts primitive type values or

strings into bytes and output the bytes to the stream.


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DataInputStream

DataInputStream extends FilterInputStream and

implements the DataInput interface.

java.io.DataInput

+readBoolean(): boolean

+readByte(): byte

+readChar(): char

+readFloat(): float

+readDouble(): float

+readInt(): int

+readLong(): long

+readShort(): short+readLine(): String

+readUTF(): String

Reads a Boolean from the input stream.

Reads a byte from the input stream.

Reads a character from the input stream.

Reads a float from the input stream.

Reads a double from the input stream.

Reads an int from the input stream.

Reads a long from the input stream.

Reads a short from the input stream.Reads a line of characters from input.

Reads a string in UTF format.

InputStream

FilterInputStream

DataInputStream

+DataInputStream(

in: InputStream)


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DataOutputStreamDataOutputStream extends FilterOutputStream and implements the

DataOutput interface.

java.io.DataOutput

+writeBoolean(b: Boolean): void

+writeByte(v: int): void

+writeBytes(s: String): void

+writeChar(c: char): void

+writeChars(s: String): void

+writeFloat(v: float): void

+writeDouble(v: float): void

+writeInt(v: int): void

+writeLong(v: long): void+writeShort(v: short): void

+writeUTF(s: String): void

Writes a Boolean to the output stream.

Writes to the output stream the eight low-order bits

of the argument v.

Writes the lower byte of the characters in a string to

the output stream.

Writes a character (composed of two bytes) to theoutput stream.

Writes every character in the string s, to the output

stream, in order, two bytes per character.

Writes a float value to the output stream.

Writes a double value to the output stream.

Writes an int value to the output stream.

Writes a long value to the output stream.Writes a short value to the output stream.

Writes two bytes of length information to the output

stream, followed by the UTF representation of

every character in the string s.

OutputStream

FilterOutputStream

DataOutputStream

+DataOutputStream(

out: OutputStream)


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Characters and Strings in Binary I/O

A Unicode consists of two bytes. The writeChar(char c)

method writes the Unicode of character c to the output.The writeChars(String s) method writes the Unicode foreach character in the string s to the output.Why UTF-8? What is UTF-8?

UTF-8 is a coding scheme that allows systems to operate with both ASCIIand Unicode efficiently. Most operating systems use ASCII. Java usesUnicode. The ASCII character set is a subset of the Unicode character set.Since most applications need only the ASCII character set, it is a waste torepresent an 8-bit ASCII character as a 16-bit Unicode character. The UTF-

8 is an alternative scheme that stores a character using 1, 2, or 3 bytes.ASCII values (less than 0x7F) are coded in one byte. Unicode values lessthan 0x7FF are coded in two bytes. Other Unicode values are coded inthree bytes.


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Using DataInputStream/DataOutputStream

Data streams are used as wrappers on existing input and

output streams to filter data in the original stream. Theyare created using the following constructors:

public DataInputStream(InputStream instream)

public DataOutputStream(OutputStream outstream)

The statements given below create data streams. The firststatement creates an input stream for file in.dat; thesecond statement creates an output stream for file

out.dat.DataInputStream infile =

new DataInputStream(new FileInputStream("in.dat"));

DataOutputStream outfile =

new DataOut utStream new FileOut utStream "out.dat"

TestDataStream Run
http://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestDataStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestDataStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestDataStream.html


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Checking End of File

TIP: If you keep reading data at the end of a stream, anEOFException would occur. So how do you check the

end of a file? You can use input.available() to check it.input.available() == 0 indicates that it is the end of a file.

Order and Format

CAUTION: You have to read the data in the same order and same format inwhich they are stored. For example, since names are written in UTF-8 usingwriteUTF, you must read names using readUTF.


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BufferedInputStream/

BufferedOutputStreamUsing buffers to speed up I/O

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

BufferedInputStream/BufferedOutputStream does not contain new methods. All

the methods BufferedInputStream/BufferedOutputStream are inherited from the

InputStream/OutputStream classes.

Constructing


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Constructing

BufferedInputStream/BufferedOutputStream

// Create a BufferedInputStreampublic BufferedInputStream(InputStream in)

public BufferedInputStream(InputStream in, int bufferSize)

// Create a BufferedOutputStream

public BufferedOutputStream(OutputStream out)

public BufferedOutputStream(OutputStreamr out, int

bufferSize)


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Case Studies: Copy File

This case study develops a program that copies files. The user

needs to provide a source file and a target file as command-linearguments using the following command:

java Copy source target

The program copies a source file to a target file and displays thenumber of bytes in the file. If the source does not exist, tell theuser the file is not found. If the target file already exists, tell theuser the file already exists. Copy Run

Obj t I/O

Optional
http://localhost/var/www/apps/conversion/tmp/scratch_6/html/Copy.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/Copy.html


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Object I/O

DataInputStream/DataOutputStream enables you to perform I/O for

primitive type values and strings. ObjectInputStream/ObjectOutputStreamenables you to perform I/O for objects in addition for primitive typevalues and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

p

Obj tI tSt


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ObjectInputStream

ObjectInputStream extends InputStream and implementsObjectInput and ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput

ObjectStreamConstants

Obj tO t tSt


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ObjectOutputStream

ObjectOutputStream extends OutputStream and implementsObjectOutput and ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void Writes an object.

ava.io.OutputStream

java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput


U i Obj t St


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Using Object Streams

You may wrap an

ObjectInputStream/ObjectOutputStream on anyInputStream/OutputStream using the following

constructors:

// Create an ObjectInputStream

public ObjectInputStream(InputStream in)

// Create an ObjectOutputStream

public ObjectOutputStream(OutputStream out)

TestObjectOutputStream Run

TestObjectInputStream Run

Random Access Files
http://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestObjectOutputStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestObjectInputStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestObjectInputStream.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/TestObjectOutputStream.html


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Random Access Files

All of the streams you have used so far are known as read-

only or write-only streams. The external files of these streamsare sequential files that cannot be updated without creating anew file. It is often necessary to modify files or to insert newrecords into files. Java provides the RandomAccessFile classto allow a file to be read from and write to at randomlocations.

RandomAccessFile


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RandomAccessFile

Creates a RandomAccessFile stream with the specified File object and

mode.

Creates a RandomAccessFile stream with the specified file name

string and mode.

Closes the stream and releases the resource associated with the stream.

Returns the offset, in bytes, from the beginning of the file to where the

next read or write occurs.

Returns the length of this file.

Reads a byte of data from this file and returns1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the

stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.

Writes b.length bytes from the specified byte array to this file, startingat the current file pointer.

Writes len bytes from the specified byte array starting at offset off to

this file.

DataInput DataInput

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode:

String)

+RandomAccessFile(name: String,

mode: String)

+close(): void

+getFilePointer(): long

+length(): long

+read(): int


+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int


+write(byte b[], int off, int len)+write(b: byte[], off: int, len: int):

void

Fil P i


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File Pointer

A random access file consists of a sequence of bytes.

There is a special marker calledfile pointerthat ispositioned at one of these bytes. A read or writeoperation takes place at the location of the file pointer.When a file is opened, the file pointer sets at the

beginning of the file. When you read or write data to thefile, the file pointer moves forward to the next data. Forexample, if you read an int value using readInt(), theJVM reads four bytes from the file pointer and now the

file pointer is four bytes ahead of the previous location.

bytefile byte byte byte byte byte byte byte byte byte byte byte

file pointer


file pointer

(A) Before readInt()

(B) Before readInt()

i M h d


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RandomAccessFile Methods

Many methods in RandomAccessFile are the same as those

in DataInputStream and DataOutputStream. Forexample, readInt(), readLong(), writeDouble(),readLine(), writeInt(), and writeLong() can be usedin data input stream or data output stream as well as inRandomAccessFile

streams.

M h d


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RandomAccessFile Methods, cont.

void seek(long pos) throws

IOException;

Sets the offset from the beginning of the

RandomAccessFile stream to where the next read

or write occurs.

long getFilePointer()

IOException;

Returns the current offset, in bytes, from the

beginning of the file to where the next read

or write occurs.

i M h d


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long length()IOException

Returns the length of the file.

final void writeChar(int v)

throws IOException

Writes a character to the file as a two-byte Unicode, with

the high byte written first.

final void writeChars(String s)

throws IOExceptionWrites a strin to the file as a se uence of

R d A Fil C t t


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RandomAccessFile Constructor

RandomAccessFile raf =

new RandomAccessFile("test.dat", "rw");//allows read and write

RandomAccessFile raf =

new RandomAccessFile("test.dat", "r");//read only

Case Studies: Address BookOptional


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Case Studies: Address Book

Now let us use RandomAccessFile to create a useful project for

storing and viewing and address book. The user interface of theprogram is shown in Figure 16.24. TheAddbutton stores a new

address to the end of the file. The First,Next, Previous, and

Lastbuttons retrieve the first, next, previous, and last addresses

from the file, respectively.

Fixed Length String I/O


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Random access files are often used to process files of

records. For convenience, fixed-length records areused in random access files so that a record can belocated easily. A record consists of a fixed number offields. A field can be a string or a primitive data type.

A string in a fixed-length record has a maximum size.If a string is smaller than the maximum size, the rest ofthe string is padded with blanks.

Record 1 Record 2 Record n

Field1 Field 2 Field k

file

e.g.,

Student 1 Student 2 Student n

name street city state zip

FixedLengthStringIO
http://localhost/var/www/apps/conversion/tmp/scratch_6/html/FixedLengthStringIO.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/FixedLengthStringIO.html


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End of Presentation

Binary Input & OutputChapter 18

Class #15 Input and OutputHow is I/O Handled in Java?


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Patrick Healy

A File object encapsulates the properties of a file or a path, but does not contain the methods for

reading/writing data from/to a file. In order to perform I/O, you need to create objects using appropriate

Java I/O classes.

Formatter output = new Formatter(outfile.txt");

output.format("%s", "Java 120"); // Write a string to outfile.txt

output.close(); // Close the output file outfile.txt

Scanner input = new Scanner(new File("temp.txt")); // Create object

System.out.println(input.nextLine()); // Read a line

Program

Input objectcreated from an

input class

Output object

created from an

output class

Input stream

Output stream

File

File010111001

110011011

Class #15 Input and OutputText Files vs. Binary Files


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Patrick Healy

Data stored in a text file are represented in human-readable form. Data storedin a binary file are represented in binary form. Youcannot read binary files.

Binary files are designed to be read by programs. For example, the Javasource programs are stored in text files and can be read by a text editor, butthe Java classes are stored in binary files and are read by the JVM. Theadvantage of binary files is that they are more efficient to process than textfiles.

Although it is not technically precise and correct, you can imagine that a textfile consists of a sequence of characters and a binary file consists of asequence of bits. For example, the decimal integer 199 is stored as thesequence of three characters: '1', '9', '9' in a text file and the same integer is

stored as a byte-type value C7 in a binary file ( Note: decimal 199 equals toHex C7.)

Class #15 Input and OutputBinary File I/O


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Patrick Healy

y

Text I/O requires encoding and decoding. The JVM converts a Unicode char to a file-

specific encoding when writing a character and coverts a file-specific encoding to a Unicode

char when reading a character. Binary I/O does not require conversions. When you write a

byte to a file, the original byte is copied into the file. When you read a byte from a file, the

exact byte in the file is returned.

Text I/O program

The Unicode of

the characterEncoding/

Decoding

Binary I/O program


(a)

e.g.

"199"

The encoding of the character

is stored in the file

0x31

e.g.

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7


Class #15 Input and OutputBinary I/O Classes Inheritance Hierarchy


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Patrick Healy

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

Class #15 Input and OutputInputStream (a byte stream class)


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Patrick Healy

java.io.InputStream

+read(): int


+read(b: byte[], off: int,len: int): int

+available(): int

+close(): void

+skip(n: long): long

+markSupported(): boolean+mark(readlimit: int): void

+reset(): void

Reads the next byte of data from the input stream. The value byte is returned asan int value in the range 0 to 255. If no byte is available because the end of

the stream has been reached, the value1 is returned.

Reads up to b.length bytes into array b from the input stream and returns the

actual number of bytes read. Returns -1 at the end of the stream.

Reads bytes from the input stream and stores into b[off], b[off+1], ,

b[off+len-1]. The actual number of bytes read is returned. Returns -1 at the

end of the stream.

Returns the number of bytes that can be read from the input stream.

Closes this input stream and releases any system resources associated with the

stream.

Skips over and discards n bytes of data from this input stream. The actualnumber of bytes skipped is returned.

Tests if this input stream supports the mark and reset methods.Marks the current position in this input stream.

Repositions this stream to the position at the time the mark method was last

called on this input stream.

The value returned is a byte as an int type.

Class #15 Input and OutputOutputStream ( a byte stream class)


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Patrick Healy

The value is a byte as an int type.

java.io.OutputStream

+write(int b): void

+write(b: byte[]): void+write(b: byte[], off: int,

len: int): void

+close(): void

+flush(): void

Writes the specified byte to this output stream. The parameter b is an int value.(byte)b is written to the output stream.

Writes all the bytes in array b to the output stream.Writes b[off], b[off+1], , b[off+len-1] into the output stream.

Closes this input stream and releases any system resources associated with thestream.

Flushes this output stream and forces any buffered output bytes to be written out.

Class #15 Input and OutputFileInputStream & FileOutputStream (byte streams)


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Patrick Healy

p p ( y )

FileInputStream/FileOutputStream associates a binaryinput/output stream with an external file. All the methods

in FileInputStream/FileOuptputStream are inherited fromits superclasses.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


FileInputStream (byte stream)


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Patrick Healy

FileInputStream (byte stream)

To construct a FileInputStream, use the following constructors:

public FileInputStream(String filename)

public FileInputStream(File file)

A java.io.FileNotFoundException would occur if you attemptto create a FileInputStream with a nonexistent file.

Class #15 Input and OutputFileOutputStream (byte stream)


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Patrick Healy

To construct a FileOutputStream, use the following constructors:public FileOutputStream(String filename)

public FileOutputStream(File file)public FileOutputStream(String filename, boolean append)

public FileOutputStream(File file, boolean append) // append = true to add on to the file

If the file does not exist, a new file would be created. If the file already exists,

the first two constructors would delete the current contents in the file. Toretain the current content and append new data into the file, use the last twoconstructors by passing true to the append parameter.

Demo Program: TestFileStream.java

Class #15 Input and OutputFilterInputStream/FilterOutputStream


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Patrick Healy

p p

Filter streams are streams that filter bytes for some purpose. The basic byte inputstream provides a read method that can only be used for reading bytes. If you want toread integers, doubles, or strings, you need a filter class to wrap the byte input stream.

Using a filter class enables you to read integers, doubles,and strings instead of bytes andcharacters. FilterInputStream and FilterOutputStream are the base classes for filteringdata. When you need to process primitive numeric types, use DataInputStream andDataOutputStream to filter bytes.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


DataInputStream & DataOutputStream (byte streams)


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Patrick Healy

DataInputStream & DataOutputStream (byte streams)

DataInputStream reads bytes from the stream andconverts them into appropriate primitive type valuesor strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataOutputStream converts primitive type values or strings into bytes and

outputs the bytes to the stream.


DataInputStream ( byte stream)


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Patrick Healy

p ( y )

DataInputStream extends FilterInputStream and implements the

DataInput interface.

java.io.DataInput

+readBoolean(): boolean

+readByte(): byte

+readChar(): char+readFloat(): float

+readDouble(): float

+readInt(): int

+readLong(): long

+readShort(): short

+readLine(): String

+readUTF(): String

Reads a Boolean from the input stream.

Reads a byte from the input stream.

Reads a character from the input stream.Reads a float from the input stream.

Reads a double from the input stream.

Reads an int from the input stream.

Reads a long from the input stream.

Reads a short from the input stream.

Reads a line of characters from input.

Reads a string in UTF format.

InputStream

FilterInputStream

DataInputStream

+DataInputStream(

in: InputStream)

Class #15 Input and OutputDataOutputStream (byte stream)


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DataOutputStream extends FilterOutputStream and implements the DataOutput interface.

java.io.DataOutput

+writeBoolean(b: Boolean): void

+writeByte(v: int): void

+writeBytes(s: String): void

+writeChar(c: char): void

+writeChars(s: String): void

+writeFloat(v: float): void

+writeDouble(v: float): void

+writeInt(v: int): void

+writeLong(v: long): void

+writeShort(v: short): void

+writeUTF(s: String): void

Writes a Boolean to the output stream.

Writes to the output stream the eight low-order bits

of the argument v.

Writes the lower byte of the characters in a string to

the output stream.

Writes a character (composed of two bytes) to the

output stream.

Writes every character in the string s, to the output

stream, in order, two bytes per character.

Writes a float value to the output stream.

Writes a double value to the output stream.

Writes an int value to the output stream.

Writes a long value to the output stream.

Writes a short value to the output stream.

Writes two bytes of length information to the output

stream, followed by the UTF representation of

every character in the string s.

OutputStream

FilterOutputStream

DataOutputStream

+DataOutputStream(

out: OutputStream)

Class #15 Input and OutputCharacters and Strings in Binary I/O


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A Unicode char is 2 bytes. The writeChar(char ch) method writes the Unicode of character chto the output. The writeChars(String str) method writes the Unicode for each character in thestring str to the output file.

What is UTF-8 ? Why use UTF-8 ? [ UTF means Unicode Text File ]

UTF-8 is a coding scheme that allows systems to operate with both ASCII and Unicode efficiently. Most

operating systems use ASCII. Java uses Unicode. The ASCII character set is a subset of the Unicodecharacter set. Since most applications need only the ASCII character set, it is a waste to represent an8-bit ASCII character as a 16-bit Unicode character. The UTF-8 is an alternative scheme that stores acharacter using 1, 2, or 3 bytes. ASCII values (less than 0x7F) (127 decimal) are coded in one byte.Unicode values less than 0x7FF are coded in two bytes. Other Unicode values are coded in three bytes.




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Data streams are used as wrappers on existing input and output streams tofilter data in the original stream. They are created using the following

constructors:public DataInputStream(InputStream instream)

public DataOutputStream(OutputStream outstream)

The statements below create data streams. The first statement creates aninput stream for file in.dat; the second statement creates an output stream forfile out.dat.

DataInputStream infile =

new DataInputStream(new FileInputStream("in.dat"));


new DataOutputStream(new FileOutputStream("out.dat"));

Demo Program: TestDataStream.java


Order and Format


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Checking for the End of File (EOF)

TIP: If the program tried to read data at the end of a stream, an EOFExceptionwould occur. How do you check the end of a file? Use input.available() tocheck for EOF. if input.available() == 0 then the program is at the end of a file.

(EOF)

Order and Format

CAUTION: You have to read the data in the same order and same format in

which they are stored. For example, if names are written in UTF-8 usingwriteUTF (String str), you MUST read the names using the readUTF method.


BufferedInputStream/


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BufferedInputStream/BufferedOutputStream Use buffers to speed up I/O processes

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

BufferedInputStream/BufferedOutputStream does not contain new methods. All the methodsBufferedInputStream/BufferedOutputStream are inherited from the InputStream/OutputStream classes.


Constructing BufferedInputStream/BufferedOutputStream


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Constructing BufferedInputStream/BufferedOutputStream

// Create a BufferedInputStream

public BufferedInputStream(InputStream in)public BufferedInputStream(InputStream in, int bufferSize)

// Create a BufferedOutputStream

public BufferedOutputStream(OutputStream out)

public BufferedOutputStream(OutputStream out, int bufferSize)

Class #15 Input and OutputCopyFile.java


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CopyFile.java is a program that copies files. The user needs to provide a sourcefile and a target file as command-line arguments using the following command:

java CopyFile source target

Also: java CompFile source target

The program copies a source file to a target file and displays the number of bytesin the file. If the source does not exist, tell the user the file is not found. If the target

file already exists, tell the user the file already exists.

Class #15 Input and OutputObject I/O (optional)


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DataInputStream/DataOutputStream enables you to perform I/O for primitive type values andstrings. ObjectInputStream/ObjectOutputStream enables you to perform I/O for objects in

addition for primitive type values and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


ObjectInputStream (optional)


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ObjectInputStream (optional)

ObjectInputStream extends InputStream and implements ObjectInput and

ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput



ObjectOutputStream (optional)


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ObjectOutputStream (optional)

ObjectOutputStream extends OutputStream and implements ObjectOutput and

ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void Writes an object.

ava.io.OutputStream

java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput


Class #15 Input and OutputUsing Object Streams (optional)


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You may wrap an ObjectInputStream/ObjectOutputStream on anyInputStream/OutputStream using the following constructors:

// Create an ObjectInputStream

public ObjectInputStream(InputStream in)

// Create an ObjectOutputStream

public ObjectOutputStream(OutputStream out)

Demo: TestObjectOutputStream.java

TestObjectInputStream.java

Class #15 Input and OutputTheSerializable Interface


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Not all objects can be written to an output stream. Objects that CANbe written to an object

stream is said to be serializable. A serializable object is an instance of the java.io.Serializable

interface. So the class of a serializable object must implement the Serializable interface.

The Serializable interface is a marker interface. It has no methods, so you don't need to add

additional code in your class that implements Serializable.

Implementing this interface enables the Java serialization mechanism to automate the process

of storing the objects and arrays.


Thetransient Keyword


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If an object is an instance of Serializable, but it contains non-serializable instance data fields,

can the object be serialized? The answer is NO !

To enable the object to be serialized, you can use the transient keyword to mark these data

fields to tell the JVM to ignore these fields when writing the object to an object stream.

Class #15 Input and OutputThetransient Keyword, cont.

Consider the following class:


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g

public class ITP120 implements java.io.Serializable {

private int v1;private static double v2;

private transient A v3 = new A();

}

class A { } // A is not serializable

When an object of the ITP120 class is serialized, only variable v1 isserialized. Variable v2 is not serialized because it is a static variable, andvariable v3 is not serialized because it is marked transient. If v3 were notmarked transient, a java.io.NotSerializableException would occur.


Serializing Arrays (optional)


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An array is serializable if all its elements are serializable. So an entire array can be saved

using writeObject into a file and later restored using readObject.

Listing 18.6 stores an array of five int values, an array of three strings, and an array of two

JButton objects, and reads them back to display on the console.

Demo Program: TestObjectStreamForArray.java


Random Access Files


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All of the streams you have used so far are known as read-onlyorwrite-onlystreams. The

external files of these streams are sequentialfiles that cannot be updated without creating

a new file.

It is often necessary to modify files or to insert new records into files. Java provides the

RandomAccessFile class to allow a file to be read from and write to at random locations.

Class #15 Input and OutputRandomAccessFile

DataInput DataInput


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Creates a RandomAccessFile stream with the specified File object andmode.

Creates a RandomAccessFile stream with the specified file name

string and mode.

Closes the stream and releases the resource associated with the stream.

Returns the offset, in bytes, from the beginning of the file to where the

next read or write occurs.

Returns the length of this file.

Reads a byte of data from this file and returns1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the

stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.

Writes b.length bytes from the specified byte array to this file, startingat the current file pointer.

Writes len bytes from the specified byte array starting at offset off to

this file.

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode:String)

+RandomAccessFile(name: String,

mode: String)

+close(): void

+getFilePointer(): long

+length(): long

+read(): int


+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int


+write(byte b[], int off, int len)+write(b: byte[], off: int, len: int):

void

Class #15 Input and OutputFile Pointers


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A random access file consists of a sequence of bytes. There is a specialmarker called file pointerthat is positioned at one of these bytes. A read or

write operation takes place at the location of the file pointer. When a file isopened, the file pointer sets at the beginning of the file. When you read orwrite data to the file, the file pointer moves forward to the next data. Forexample, if you read an int value using readInt(), the JVM reads four bytesfrom the file pointer and now the file pointer is four bytes ahead of the

previous location.

Class #15 Input and OutputFile Pointers

(moving the pointer 4 bytes ahead)


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file pointer


file pointer

(A) Before readInt()

(B) Before readInt()


RandomAccessFile Methods


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Many methods in RandomAccessFile are the same as those in

DataInputStreamand DataOutputStream.

For example, readInt(), readLong(),writeDouble(), readLine(),writeInt(), andwriteLong()

can be used in data input stream or data output stream as well as inRandomAccessFile streams.

Class #15 Input and OutputRandomAccessFile Methods, cont.

void seek(long pos) throws IOException;


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void seek(long pos) throws IOException;

Sets the offset from the beginning of the RandomAccessFile stream to

where the next reador write occurs.

long getFilePointer() IOException;

Returns the current offset, in bytes, from the

beginning of the file to where the next reador write occurs.




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long length()IOException

Returns the length of the file.

final void writeChar(int v) throwsIOException

Writes a character to the file as a two-byte Unicode, with the high byte written

first.

final void writeChars(String s)throws IOException

Writes a string to the file as a sequence of

characters.


RandomAccessFile Constructors


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RandomAccessFile raf =new RandomAccessFile("test.dat", "rw"); //allows read

and write to the file

RandomAccessFile raf =new RandomAccessFile("test.dat", "r"); //read only

Demo program: TestRandomAccessFile.java

(uses FixedLengthStringIO.java)

Case Study: Address Book


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Now let us use RandomAccessFile to create a useful project for

storing and viewing and address book. The user interface of the

program is shown in Figure 16.24. TheAddbutton stores a new

address to the end of the file. The First,Next, Previous, and

Lastbuttons retrieve the first, next, previous, and last addresses

from the file, respectively.

Run: AddressBook.java which uses FixedLengthStringIO.java



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Random access files are often used to process files of

records. For convenience, fixed-length records areused in random access files so that a record can belocated easily. A record consists of a fixed number offields. A field can be a string or a primitive data type.

A string in a fixed-length record has a maximum size.If a string is smaller than the maximum size, the rest ofthe string is padded with blanks.

Record 1 Record 2 Record n

Field1 Field 2 Field k

file

e.g.,

Student 1 Student 2 Student n

name street city state zip

FixedLengthStringIO

Chapter 18 Demo Programs
http://localhost/var/www/apps/conversion/tmp/scratch_6/html/FixedLengthStringIO.htmlhttp://localhost/var/www/apps/conversion/tmp/scratch_6/html/FixedLengthStringIO.html


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78

ReadBytes.java (skip) WriteData.java

WriteDemo.java ReadData.java

ShowFile.java

CopyFile.java CopyFileUsingByteStream.java

CompFile.java

RWData.java

RandomAccessDemo.java

PrintWriterDemo.javaReadChars.java or BuffReader.java

ReadLines.java (BufferedReader)



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79

TextFileScannerDemo.java

Uses input file morestuff.txt

HasNextLineDemo.java

Uses input file original.txt

and creates output file numbered.txt BufferReaderDemo.java

Uses input file: buffer.txt



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80

TestDataStreams.java

TestFileClass.java

TestPrintWriters.java

ViewFile.java (GUI text file viewer program)

needs MyFrameWithExitHanding.java class file

ParsingTextFile.java (needs grades.dat file)

(creates gradesout.dat)

TestRandomAccessFile.java

AddressBook.java (creates file address.dat)

needs FixedLengthStringIO.class file



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81

TestDataStream.java

TestFileReader.java (needs temp.txt)

TestFileStream.java

TestFileWriter.java (needs testdata.txt)

TestObjectStreamForArray.java ( creates array.dat)

TestObjectOutputStream.java

(creates object.dat)

TestObjectInputStream.java (reads object.dat)

Class #15 Input and OutputChapter 18 Input / Output


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Optional: More on Java File I/O

Chapter 18 Java I ITP 120

Class #15 Input and OutputChapter 18: More on Input and Output

Stream Classes (byte & character streams)Predefined Streams (System in System out System err)


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Predefined Streams (System.in, System.out, System.err)

Processing External Files

Data Streams

Print Streams

Buffered Streams

Text Input and Output on the Console

Random Access Files

Class #15 Input and OutputChapter 18 Input /Output Objectives

Understand input & output streams and learn how to create them.


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Discover the uses of byte and character streams.

To know how to read from / write to external files using file streams. To become familiar with the File class.

To use print streams to output data of primitive types in text format.

To know how to read and write text data files.

Use text input and output on the console.

Use RandomAccessFile for reading & writing random access files.

Class #15 Input and OutputOverview

The java.io.*package provides a library of classes to read and writevarious types of data


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various types of data.

In Java, all data I/O is handled in the form of streams

Data streams can be byte streams or character streams

The java.io package has classes that process byte streams of all types

NOTE: In Java, a character is 2 BYTES !

NOTE: Unicode character is 2 bytes !

The Reader and Writer classes process character streams.

Streams can be layered, so that one type of streams can be convertedto another type of streams by chaining. Chaining a character streamreader to a byte stream reader to read bytes on one end and produce

characters at the other end .

Class #15 Input and OutputOverview Streams

In Java, all Input/Output is handled by streams


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A stream is an abstraction of the continuous one-way flow of data

Java streams can be applied to any source of data, so it is easy to getinput from the keyboard and send output to a monitor, and the same

applies to file input & output.

All streams EXCEPT random-access file streams flow only in one

direction.

See the diagram on the next slide

Class #15 Input and OutputOverview --- Streams


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A stream is an abstraction of a continuous one-way flow of data.

Program

Output Stream

File

Input Stream

Class #15 Input and OutputOverview and Background

The original version of Java defined only the byte stream, but character

streams were quickly added


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streams were quickly added.

Byte streams can be used when reading or writing binary data. Character streams are designed for handling character I/O.

Character streams use UNICODE. In Java, a character is 2 bytes

Unicode is for the internationalization of Java in different languages.

The Java I/O system is quite LARGE because of the TWO separateclass hierarchies of bytes and streams.

How is I/O Handled in Java?A File object encapsulates the properties of a file or a path, but does not contain


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the methods for reading/writing data from/to a file. In order to perform I/O, you

need to create objects using appropriate Java I/O classes.

Formatter output = new Formatter("temp.txt");output.format("%s", "Java ITP 120");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program

Input object

created from aninput class

Output object

created from an

output class

Input stream

Output stream

File

File010111001

110011011

Class #15 Input and OutputText Files vs. Binary Files

Data stored in a text file are represented in human-readable form. Data


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pstored in a binary file are represented in binary form. You cannot read

binary files. Binary files are designed to be read by programs. For example,the Java source programs are stored in text files and can be read by a texteditor, but the Java classes are stored in binary files and are read by theJVM.

The advantage of binary files is that they are more efficient to process than

text files.

Although it is not technically precise and correct, you can imagine that atext file consists of a sequence of characters and a binary file consists of asequence of bits. For example, the decimal integer 199 is stored as the

sequence of three characters: '1', '9', '9' in a text file and the same integer isstored as a byte-type value C7 in a binary file, because decimal 199 equalsto hex C7 ( 12 x 16 + 7 = 192 + 7 = 199 decimal )

Binary I/O

Text I/O requires encoding and decoding. The JVM converts a Unicode


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character to file-specific encoding when writing a character, and coverts

a file-specific encoding to a Unicode character when reading a character.Binary I/O does not require conversions. When you write a byte to a file,

the original byte is copied into the file. When you read a byte from a file,

the exact byte in the file is returned.

Text I/O program

The Unicode of

the character

Encoding/

Decoding

Binary I/O program


(a)

e.g.

"199"

The encoding of the character

is stored in the file

0x31

e.g.

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7


Class #15 Input and Output2 Types of Stream Classes: Bytes & Characters



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character streams.

The InputStream/OutputStreamclass is the

root of all byte stream classes

The Reader/Writer class is the root of all character stream

classes.

The subclasses ofInputStream/OutputStreamare analogous to thesubclasses ofReader/Writer.

Class #15 Input and OutputByte Stream Classes (note: stream )

DataInputStream

FileInputStream

ByteArrayInputStreamInputData


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InputStream

OutputStream

RandomAccessFile

Object

PipeOutputStream

SequenceInputStream

StringBufferInputStream

ByteArrayOutputStream

ObjectOutputStream

FilterOutputStream

FileOutputStream

PipedInputStream

PushBackInputStream

BufferedInputStream

LineNumberInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

OutputData

ObjectOutput

ObjectInput

Class #15 Input and OutputCharacter Stream Classes (Character = 2 bytes)

FileReaderInputStreamReader

CharArrayReader


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Reader

Writer

StreamTokenizer

Object

PrintWriter

BufferedWriter

CharArrayWriter

PipedWriter

FilterWriter

PipedReader

LineNumberReader

PushBackReader

FileWriter

StringWriter

StringReader

BufferedReader

FilterReader

OutputStreamWriter


Predefined Streams in Java

All Java programs automatically import the java.lang package.


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The java.lang package defines a class called System whichencapsulates several aspects of the runtime environment.

The System class contains 3 predefined stream variables called:

in, out, and err (System.in, System.out, System.err)

These variables are declared as public and static with the System

class. This means they can be used by any other part of your program

and without a reference to a specific object in the System class.

Class #15 Input and OutputPredefined Streams in Java: System class

System.in refers to the standard input stream which is the

keyboard by default. (Keyboard )


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y y ( y )

System.out refers to the standard output stream which is the

console by default. (Monitor)

System.err refers to the standard error stream which is also theconsole by default. (Monitor)

These streams may be redirected to any compatible I/O device.


Predefined Streams in Java: System class

System.in is an object of type InputStream. (byte stream)


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System.out is an object of type PrintStream. (byte stream)

System.err is an object of type PrintStream. (byte stream)

They are all byte streams and are a part of the original Javaspecification.

They are NOT character streams ! (Unicode character = 2 bytes)


Reading Keyboard Input

// Read an array of bytes from the keyboard.

import java.io.*;


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public class ReadBytes {

public static void main(String[ ] args)throws IOException {

byte data[ ] = new byte[10]; // Byte array data holds 10 bytes

System.out.println("Enter some characters:");

System.in.read(data); // Use the read method to read some bytes

System.out.print("You entered: ");

for(int i=0; i < data.length; i++)

System.out.print((char) data[i]); // Cast data to a character

} // End main method

} // End class ReadBytes


Reading Keyboard Input

Here is a sample run from the previous program:


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Enter some characters: (prompt from program)READ BYTES (User entered READ BYTES)

You entered: READ BYTES (output from program)


Writing Output to the Monitor

// Demonstrate System.out.write(). Java program WriteDemo.java

public class WriteDemo


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{

public static void main(String[ ] args)

{

int b; // Program prints an X on the monitor

b = 'X'; // The character is an int

System.out.write(b); // A byte stream; write low-order 8 bits

System.out.write('\n'); // Print a newline character \n

} // End of main( ) // print() and println() are easier to use than write()

} // End of class WriteDemo


Stream classes (Bytes & Characters)

The java.io package provides two categories of classes: Byte stream readers and writers

Ch t t d d it


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Character stream readers and writers

At the top of the hierarchy for stream classes are the abstract classesInputStream and Output Stream

The subclasses branch out and specializes into the different types ofstreams that they handle.

InputData, OutputData, and ObjectInput interfaces are implemented bythe classes that handle data, such as, int, double, char, etc., andobjects. Only ObjectInput specifies methods for reading objects.

DataInputStream - which is a subclass of FilterInputStream, which inturn is a subclass of InputStream implements the InputData interface

and can read primitive data, and objects from byte streams.


Stream Classes

FileInputStream can read raw streams of data from files.

DataOutputStream can write primitive data; this class implements the


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p p ; p

OutputData interface

RandomAccessFile implements both InputData and OutputData

interfaces, therefore, it can read and write data to streams.

ObjectOutputStream implements the ObjectOutputinterface and can

write object data to streams.


InputStream Class (for reading bytes)

The following methods are defined in InputStream


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and are often useful:

public abstract int read() throws IOException

Reads the next byte and returns its value in therange of 0 to 255. At the end of the stream, itreturns a - 1.

public int read(byte b[]) throws IOExceptionReads bytes into array b,, returns b.length if thenumber of available bytes is >= b.length. Returnsthe number of bytes read if the number of available

bytes is < than b.length, and returns 1 at the endof the stream.



The following methods are defined in InputStream and


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are often useful:

public void close() throws IOException

This method closes the input stream.

public void available() throws IOException

Returns the number of bytes that can be read fromthe input stream without blocking.



The following method is defined in InputStream and isf f l


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often useful:

public long skip(long n) throws IOException

Skip over and discard n bytes of data from theinput stream. The actual number of bytes skipped

is returned.


Reading & Writing Files Using Byte Streams

To create a byte stream linked to a file, use FileInputStream or

FileOutputStream


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To open a file, create an object of one of these classes, specifying the

name of the file as an argument to the constructor.

Once the file is open, you can read from the file or write to the file.

To read form a file, you may use the read( ) method.

int read( ) throws IOException

When you are done with a file, you should close it by calling close()

void close( ) throws IOException

Closing a file releases the system resources allocated to the file,

allowing them to be used by another file.



/* Display a text file.

To use this program, specify the name


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of the file that you want to see.For example, to see a file called TEST.TXT,

use the following command line.

Command line usage: java ShowFile TEST.TXT */

// Program ShowFile.java follows on the next slide ->



public class ShowFile {

public static void main(String[ ] args)

throws IOException {


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p {

int i;

FileInputStream fin; // Declare file pointer

try {

fin = new FileInputStream(args[0]); } // Open the input file

catch(FileNotFoundException exc) {

System.out.println(Error: + exc.getMessage( ));

System.out.println("File Not Found");

return; }

} catch(ArrayIndexOutOfBoundsException exc) {


System.out.println("Usage is: java ShowFile File.txt ");

return; }



// Read bytes until EOF is encountered

do {


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i = fin.read( ); // Read an integerif(i != -1) System.out.print((char) i); // Cast the int as a char

} while( i != -1); // When i = -1, EOF is encountered

fin.close( ); // Close the input file

} // End of main method

} // End of class ShowFile


Writing to a File Using Byte Streams

/* Java program to Copy a text file.

To use this program, specify the name


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of the source file and the destination file.For example, to copy a file called File1.txt

to a file called File2.txt , use the following

on the command line:

Usage: java CopyFile File1.txt File2.txt */



// CopyFile.java Demo byte stream file operations

import java.io.*;


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public class CopyFile {public static void main(String[ ] args) throws IOException

{

int i;

FileInputStream fin; // Declare 2 byte stream files (pointers)

FileOutputStream fout; // Output file pointer



try { // outer try block


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// try to open input file

try { // inner try

fin = new FileInputStream(args[0]);

} catch(FileNotFoundException exc) {System.out.println(Error:

+ exc.getMessage( ) );

System.out.println("Input File Not Found");

return; }



// open output file

try {


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fout = new FileOutputStream(args[1]);} catch(FileNotFoundException exc) {

System.out.println(Error: + exc.getMessage());

System.out.println("Error Opening Output File");

return;

}

} // End of outer try block



catch(ArrayIndexOutOfBoundsException exc) {

System.out.println(Error: + exc.getMessage( ) );

System.out.println("Usage: CopyFile File1 File2");


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return; }try { // Try to copy file1 to file2

do {

i = fin.read( ); // Read a byte

if(i != -1) fout.write(i); // Write the byte to the output file

} while(i != -1); // Loop while not at EOF (-1)} // End of try block

catch(IOException exc)

{ System.out.println("File Error"); }

fin.close( ); // Close the input file

fout.close( ); // Close the output file

} // End of main( ) method

} // End of class CopyFile


Reading & Writing Binary Data

So far, we have been reading and writing bytes containingASCIIbytes.

You may want to create a file that contains other types of data such as

integers doubles or shorts that is: int double short etc


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integers, doubles, or shorts , that is: int, double, short, etc.

In Java, to read and write binary values of the simple Java data types,

you should use:

DataInputStream and DataOutputStream (for binary data)

DataOutputStream implements the OutputData interface.

The OutputDatainterface defines methods that write all of Javas

simple data types to a file.



Note: Binary data is NOT in human-readable text format, obviously.


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The constructor for DataOutputStream is:

DataOutputStream(OutputStream outputStream)

outputStream is the stream to which the binary data is written.



The constructor for DataInputStream is:

DataInputStream(InputStream inputStream)


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inputStream is the stream that is linked to the instance of

DataInputStream being created.

DataInputStream implements the DataInputinterface which providesthe methods for reading all of Javas simple data types.

DataInputStream uses an InputStream instance as its foundation,

overlaying it with methods that read the various Java data types.


Reading & Writing Binary Data Examples

To create an input stream for the file in.dat ( bytes)


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DataInputStream infile =new DataInputStream(new FileInputStream(in.dat));

To create an output stream for the file out.dat:


new DataOutputStream(new FileOutputStream(out.dat));



Common Input Methods Defined by DataInputStream (a byte stream)

Input Method Purpose

boolean readBoolean ( ) Reads a boolean


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boolean readBoolean ( ) Reads a boolean

byte readByte ( ) Reads a byte

char readChar ( ) Reads a char

double readDouble( ) Reads a double

float readFloat ( ) Reads a floatint readInt ( ) Reads an int

long readLong ( ) Reads a long

short readShort ( ) Reads a short



Common Output Methods Defined by DataOutputStream ( byte stream)

Output Method Purpose

void writeBoolean (boolean val) writes the boolean specified by val


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void writeBoolean (boolean val) writes the boolean specified by val

void writeByte (int val) writes the low-order byte val

void writeChar(int val) writes the value val as a char

void writeDouble(double val) writes the double val

void writeFloat(float val) writes the float valvoid writeInt(int val) writes the int val

void writeLong(long val) writes the long val

void writeShort(int val) writes val as a short



Here is a Java program that demonstrates DataOutputStream and

DataInputStream. It writes and then reads back various types of data

to and from a file.


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// Write and then read back binary data.

import java.io.*;

public class RWData {

public static void main(String[ ] args) throws IOException

{

DataOutputStream dataOut; // Declare output, input file pointers

DataInputStream dataIn;



int i = 120;

double d = 1049.56;

boolean b = true;


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;

try {

dataOut = new

DataOutputStream(new FileOutputStream(testdata")); }

catch(IOException exc) {


System.out.println("Cannot open file.");

return; }



try { // W

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