JAVA Compilation and Interpretation JAVA Platform Independence Building First JAVA Program ...
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JAVA Compilation and Interpretation JAVA Platform Independence Building First JAVA Program Escapes Sequences Display text with printf Data types in Java Constants and Variables
JAVA Compilation and Interpretation
Text Editor/ IDE
Compiler Interpreter
Programmer
Source Code
.java file
Byte Code
.class file
Hardware and Operating System
Notepad, emacs,vi, Netbeans, Eclipse etc.,
javac
javaappletviewer
JAVA Platform Independence
JAVA COMPILER
JAVA BYTE CODE
JAVA INTERPRETER
Windows Macintosh Solaris Windows NT
(translator)
(same for all platforms)
(one for each different system)
JAVA Platform Independence
Java Compiler - Java source code (file with extension .java) to bytecode (file with extension .class)
Bytecode - an intermediate form, closer to machine representation
A interpreter (virtual machine) on any target platform interprets the bytecode.
Building First JAVA Program
//This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.printf(“%s”, “Welcome to Java!”); }}
Welcome.java
Building First JAVA Program
Trace a Program Execution
//This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.printf(“%s”, “Welcome to Java!"); }}
First line indicates comment. Which is not compiled by the JAVAPublic Specifies that the method is accessible from anywhere Class is keyword and Welcome is a java identifier that specifies the name of
the class to be defined. Static is keyword, the main must always be declared as static since the
interpreter uses this method before any objects are created. Void is an modifier that states the main method does not return any value. This is similar to the printf() statement of C.
Escape Sequences
Escape sequence
Description
\n Newline. Position the screen cursor at the beginning of the next line.
\t Horizontal tab. Move the screen cursor to the next tab stop. \r Carriage return. Position the screen cursor at the beginning of the
current line—do not advance to the next line. Any characters output after the carriage return overwrite the characters previously output on that line.
\\ Backslash. Used to print a backslash character. \" Double quote. Used to print a double-quote character. For example,
System.out.println( "\"in quotes\"" );
displays
"in quotes"
Display Text with printf
System.out.printf
Feature added in Java SE 5.0Displays formatted data
Format string Fixed text Format specifier – placeholder for a value
Format specifier %s – placeholder for a string
System.out.printf( "%s\n%s\n", "Welcome to", "Java Programming!" );
Data types in JAVA
Although complex data values are represented using objects, Java defines a set of primitive types to represent simple data.
Java provides eight primitive data types, they are boolean char, byte, short, int, long float, double
Primitive Data Types
Size in Bytes
Size in Bits
int 4 32
long 8 64
float 4 32
double 8 64
char 2 16
boolean (boolean in Java)
1 8
Primitive Data types in JAVA
A data type is defined by a set of values called the domain and a set of operations. The following table shows the data domains and common operations for all eight of Java’s primitive types:
Type
short
int
long
float
double
char
boolean
8-bit integers in the range –128 to 127
16-bit integers in the range –32768 to 32767
32-bit integers in the range–2146483648 to 2146483647
64-bit integers in the range–9223372036754775808 to 9223372036754775807
32-bit floating-point numbers in the range± 1.4 x 10-45 to ± 3.4028235 x 10-38
64-bit floating-point numbers in the range± 4.39 x 10-322 to ± 1.7976931348623157 x 10308
16-bit characters encoded using Unicode
the values true and false
The arithmetic operators:+-
*/%
addsubtract
remainderdividemultiply
= =<
!=<=>=
equal toless than
greater or equalless or equalnot equal
> greater than
The arithmetic operators except %
The relational operators:
The relational operators
The relational operators
The logical operators:&& add || or ! not
Domain Common operations
byte
Constants and Variables
The simplest terms that appear in expressions are constants and variables. The value of a constant does not change during the course of a program. A variable is a name for memory location, in which value can be stored this value may be changed at the time of execution.
Each variable has the following attributes: A name, which enables you to differentiate one variable from another. A type, which specifies what type of value the variable can contain. A value, which represents the current contents of the variable.
A variable in Java is most easily envisioned as a box capable of storing a value.
total
42
Variable Declaration In Java, you must declare a variable before you can use it. The declaration
establishes the name and type of the variable and, in most cases, specifies the initial value as well.
type name = value;
The most common form of a variable declaration is
where type is the name of a Java primitive type or class, name is an identifier that indicates the name of the variable, and value is an expression specifying the initial value.
RULES:1. First character should be an alphabet and remaining characters can be alpha-numeric.
2. Keywords cannot be used for defining.
3. No special symbols are allowed expect underscore and dollar.
4. Java is case sensitive, “Num” and “NUM” are different.
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