INF120 Basics in JAVA Programming AUBG, COS dept Lecture 03 Title: Building Java programs using...

INF120 Basics in JAVA ProgrammingAUBG, COS dept

Lecture 03Title:

Building Java programs using Command Line

Window

Reference: 1

Lecture Contents:

• Anatomy of a Java program (reminder)• More on elementary Java

– Input/Output dialogs

• Programming Style and Documentation• Building Java programs using DOS

command lines

Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 3

A Simple Java Program

//This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); }}

Listing 1.1


Two More Simple Examples

RunRunWelcomeWithThreeMessagesWelcomeWithThreeMessages

RunRunComputeExpressionComputeExpression


Anatomy of a Java Program Class name Main() method Statements Statement terminator Reserved words Comments Blocks



Class Name

Every Java program must have at least one class. Each class has a name. By convention, class names start with an uppercase letter. In this example, the class name is Welcome.



Main Method

Line 2 defines the main method. In order to run a class, the class must contain a method named main. The program is executed from the main() method.



StatementA statement represents an action or a sequence of actions. The statement

System.out.println("Welcome to Java!"); in the program below is a statement to display the greeting "Welcome to Java!“.



Statement Terminator

Every statement in Java ends with a semicolon (;).



Reserved wordsReserved words or keywords are words that have a specific meaning to the compiler and cannot be used for other purposes in the program. For example, when the compiler sees the word class, it understands that the word after class is the name for the class.


Blocks

A pair of braces in a program forms a block that groups

components of a program.

public class Test { public static void main(String[] args) { System.out.println("Welcome to Java!"); } }

Class block

Method block

Java Programming, Fifth Edition 12

Punctuation Name Typical use Alternate names

( ) Parentheses Round brackets

{ } Curly braces Curly brackets

[ ] Square brackets

Box brackets,

Square braces

< > Angle brackets Chevron is <> with nothing in

Don’t confuse names parentheses, curly braces, square brackets, and angle brackets


Special Symbols

Character Name Description

{}

() [] // " "

;

Opening and closing braces

Opening and closing parentheses

Opening and closing brackets

Double slashes

Opening and closing quotation marks

Semicolon

Denotes a block to enclose statements.

Used with methods.

Denotes an array. Precedes a comment line. Enclosing a string (i.e., sequence of characters).

Marks the end of a statement.


// This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); }}

{ … }



( … )



;



// …



" … "


Programming Style and Documentation

Appropriate Comments Naming Conventions Proper Indentation and Spacing

Lines Block Styles


Appropriate Comments

Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses.

Include your name, class section, instructor, date, and a brief description at the beginning of the program.


Naming Conventions Choose meaningful and descriptive names. Variables and method names:

– Use lowercase. If the name consists of several words, concatenate all in one, use lowercase for the first word, and capitalize the first letter of each subsequent word in the name. For example, the variables radius and area, and the method computeArea.

Class names: – Capitalize the first letter of each word in the name. For example,

the class name ComputeArea, and the class name ComputeExpression.

Constants: – Capitalize all letters in constants, and use underscores to connect

words. E.g. the constant PI, and MAX_VALUE

–


Proper Indentation, Spacing, Block Styles Indentation

– Indent two spaces. Spacing

– Use blank line to separate segments of the code. Use end-of-line style for braces.

Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved.


.

More

on

Elementary Java



JOptionPane - Input

For now Two ways of obtaining input are to be discussed.

1. Using the Scanner class (console input)1. And methods like nextInt(), nextDouble(), hasNext(), …

2. Using JOptionPane input dialogs1. And method showInputDialog() – to introduce now



Problem: Computing Loan Payments

ComputeLoanComputeLoan RunRun

This program lets the user enter the interest rate, number of years, and loan amount, and computes monthly payment and total payment.

12)1(11

arsnumberOfYeerestRatemonthlyInt

erestRatemonthlyIntloanAmountmentmonthlyPay



Getting Input from Input Dialog Boxes String inp;

inp=JOptionPane.showInputDialog("Enter an input");

// OR

String inp = JOptionPane.showInputDialog(

"Enter an input");



Getting Input from Input Dialog Boxes String string = JOptionPane.showInputDialog(

null, “Prompting Message”, “Dialog Title”,

JOptionPane.QUESTION_MESSAGE);



Converting Strings to Integers

The input returned from the input dialog box is a string. If you type a numeric value such as 123, it returns “123”. To obtain the input as a number, you have to convert a string into a number. To convert a string into an int value, you can use the static parseInt() method in the Integer class as follows: int intValue = Integer.parseInt(intString); where intString is a numeric string such as “123”.



Converting Strings to Doubles

To convert a string into a double value, you can use the static parseDouble() method in the Double class as follows:

double doubleValue =Double.parseDouble(doubleString);

where doubleString is a numeric string such as “123.45”.



Problem: Computing Loan Payments Using Input Dialogs

ComputeLoanUsingInputDialogComputeLoanUsingInputDialog RunRun

Same as the program for computing loan payments, except that the input is entered from the input dialogs and the output is displayed in an output dialog.

12)1(11

arsnumberOfYeerestRatemonthlyInt

erestRatemonthlyIntloanAmount



JOptionPane - Output

For now Two ways of sending output are to be discussed.

1. Using the System class, the out object1. And methods System.out.print(), System.out.println()

2. Using JOptionPane message dialogs1. And method showMessageDialog() – to introduce now


Displaying Text in a Message Dialog Box

you can use the showMessageDialog( ) method in the JOptionPane class. JOptionPane is one of the many predefined classes in the Java system, which can be reused rather than “reinventing the wheel.”


The showMessageDialog Method JOptionPane.showMessageDialog(null, "Welcome to Java!", "Display Message", JOptionPane.INFORMATION_MESSAGE);

34

.

Building

Java programsOr

How Java works?What processing takes place?


Compiling Java Source CodeYou can port a source program to any machine with appropriate compilers. The source program must be recompiled, however, because the object program can only run on a specific machine. Nowadays computers are networked to work together. Java was designed to run object programs on any platform. With Java, you write the program once, and compile the source program into a special type of object code, known as bytecode. The bytecode can then run on any computer with a Java Virtual Machine, as shown below. Java Virtual Machine is a software that interprets Java bytecode.

Java Bytecode

Java Virtual Machine

Any Computer

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Executing a Java program

38

JVM emulation run on a physical machine

39

JVM handles translations

40

Java Popularity

• Pure Java includes 3 software facilities:

• JRE

• JVM

• JDK

41

JRE

• The Java Runtime Environment (JRE) provides– the libraries,– the Java Virtual Machine, and– other components to run

applets and applications written in Java.

42

JVM - Overview• Java Virtual Machine is a program which executes certain

other programs, namely those containing Java bytecode instructions.

• JVM is distributed along with Java Class Library, a set of standard class libraries (in Java bytecode) that implement the Java application programming interface (API). These libraries, bundled together with the JVM, form the Java Runtime Environment (JRE).

• JVMs are available for many hardware and software platforms. The use of the same bytecode for all JVMs on all platforms allows Java to be described as a write once, run anywhere programming language, versus write once, compile anywhere, which describes cross-platform compiled languages.

• Oracle Corporation, the owner of the Java trademark, produces the most widely used JVM, named HotSpot, that is written in the C++ programming language.

http://en.wikipedia.org/wiki/Java_Class_Library

http://en.wikipedia.org/wiki/Standard_library

http://en.wikipedia.org/wiki/Application_programming_interface

http://en.wikipedia.org/wiki/Java_Runtime_Environment

http://en.wikipedia.org/wiki/Computing_platform

http://en.wikipedia.org/wiki/Write_once,_run_anywhere

http://en.wikipedia.org/wiki/Write_once,_compile_anywhere

http://en.wikipedia.org/wiki/Compiled_language

http://en.wikipedia.org/wiki/Oracle_Corporation

http://en.wikipedia.org/wiki/Trademark

http://en.wikipedia.org/wiki/HotSpot

http://en.wikipedia.org/wiki/C%2B%2B

43

JRE – Execution Environment

• Oracle's Java execution environment is termed the Java Runtime Environment, or JRE.

• Programs intended to run on a JVM must be compiled into Java bytecode, a standardized portable binary format which typically comes in the form of .class files (Java class files). A program may consist of many classes in different files. For easier distribution of large programs, multiple class files may be packaged together in a .jar file (short for Java archive).

• The Java application launcher, java, offers a standard way of executing Java code.

• The JVM runtime executes .class or .jar files, emulating the JVM instruction set by interpreting it or using a just-in-time compiler (JIT) such as Oracle's HotSpot. JIT compiling, not interpreting, is used in most JVMs today to achieve greater speed

http://en.wikipedia.org/wiki/Class_(file_format)

http://en.wikipedia.org/wiki/Java_class_file

http://en.wikipedia.org/wiki/Jar_(file_format)

http://en.wikipedia.org/wiki/Run-time_system

http://en.wikipedia.org/wiki/Emulator

http://en.wikipedia.org/wiki/Instruction_set

http://en.wikipedia.org/wiki/Interpreter_(computing)

44

JVM • JVM architecture.

Source code is compiledto Java bytecode, whichis verified, interpreted orJIT-compiled for thenative architecture. The Java APIs and JVMtogether make up theJava Runtime Environment(JRE).

45

JDK contents

The JDK has as

its primary components a collection

of programming tools, including:

46

JDK contents• appletviewer – this tool can be used to run and debug Java

applets without a web browser • apt – the annotation-processing tool4 • extcheck – a utility which can detect JAR-file conflicts • idlj – the IDL-to-Java compiler. This utility generates Java

bindings from a given Java IDL file. • java – the loader for Java applications. This tool is an

interpreter and can interpret the class files generated by the javac compiler. Now a single launcher is used for both development and deployment. The old deployment launcher, jre, no longer comes with Sun JDK, and instead it has been replaced by this new java loader.

• javac – the Java compiler, which converts source code into Java bytecode

• javadoc – the documentation generator, which automatically generates documentation from source code comments

• jar – the archiver, which packages related class libraries into a single JAR file. This tool also helps manage JAR files.

47

JDK contents (cont.)• javah – the C header and stub generator, used to write

native methods • javap – the class file disassembler • javaws – the Java Web Start launcher for JNLP

applications • JConsole – Java Monitoring and Management Console • jdb – the debugger • jhat – Java Heap Analysis Tool (experimental) • jinfo – This utility gets configuration information from a

running Java process or crash dump. (experimental) • jmap – This utility outputs the memory map for Java and

can print shared object memory maps or heap memory details of a given process or core dump. (experimental)

• jps – Java Virtual Machine Process Status Tool lists the instrumented HotSpot Java Virtual Machines (JVMs) on the target system. (experimental)

• jrunscript – Java command-line script shell

48

JDK contents (cont.)• jstack – utility which prints Java stack traces of Java

threads (experimental) • jstat – Java Virtual Machine statistics monitoring tool

(experimental) • jstatd – jstat daemon (experimental) • keytool – tool for manipulating the keystore • pack200 – JAR compression tool • policytool – the policy creation and management tool,

which can determine policy for a Java runtime, specifying which permissions are available for code from various sources

• VisualVM – visual tool integrating several command-line JDK tools and lightweight[] performance and memory profiling capabilities

• wsimport – generates portable JAX-WS artifacts for invoking a web service.

• xjc – Part of the Java API for XML Binding (JAXB) API. It accepts an XML schema and generates Java classes


Creating, Compiling, and Running Programs

Source Code

Create/Modify Source Code

Compile Source Code i.e., javac Welcome.java

Bytecode

Run Byteode i.e., java Welcome

Result

If compilation errors

If runtime errors or incorrect result

public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } }

… Method Welcome() 0 aload_0 … Method void main(java.lang.String[]) 0 getstatic #2 … 3 ldc #3 <String "Welcome to Java!"> 5 invokevirtual #4 … 8 return

Saved on the disk

stored on the disk

Source code (developed by the programmer)

Byte code (generated by the compiler for JVM to read and interpret, not for you to understand)

Creating, Compiling & Running Java

How is the required processing realized?

From the Command Line Window

From within IDEs

Creating, Compiling and Running Java from Command Line Window

First: to open a Command Window– Click Start; Select Run…; Type cmd

Second: to create a separate directory/folder on C: drive or Q: drive where to save .java and .class files– md INF120Progs– cd INF120Progs

Third: to Set path to JDK bin directory– Already done by OCC

Fourth: to create and save Java source file– Notepad/Write Welcome.java

Fifth: to Compile– javac Welcome.java

Sixth: to Run– java Welcome

Creating and Editing Using NotePadTo use NotePad, type

notepad Welcome.java from the DOS prompt.

Creating and Editing Using WordPadTo use WordPad, type

write Welcome.java from the DOS prompt.

Creating, Compiling, and Running Java Programs

In order to compile your Java program, you should type

javac Welcome.java In order to run your compiled to bytecode

Java program, you should type

java Welcome

Creating, Compiling, and Running Java Programs

Training session:– Create, compile and run the Java version of the “Hello, World!!!” program


Saving, Compiling, and Running,and Modifying a Java Application

• Saving a Java class– Save class in file with exactly same name and .java

extension• For public classes• Class name and filename must match exactly

• Compiling a Java class– Compile source code into bytecode

• Type javac First.java– Translate bytecode into executable statements Using

Java interpreter• Type java First


Saving, Compiling, and Runningand Modifying a Java Application

(continued)• Compilation outcomes

– Javac unrecognized command– Program language error messages– No messages indicating successful completion

• Reasons for error messages– Misspelled command javac– Misspelled filename– Not within correct subfolder or subdirectory on

command line– Java not installed properly


Running a Java Application

• Class (file named First.class as result/output of Java compilation) stored in folder named for example– Java on C drive

Or– in folder INF120Progs on Q drive

• Run application from command line– Type java First

• Shows application’s output in command window

Modifying a Java Class• Modify text file that contains existing class

• Save file with changes – Using same filename

• Compile class with javac command

• Interpret class bytecode and execute class using java command

• TASK:

• Modify your “Hello, world!” program to a program that displays your name, your e-mail address and your postal address, each topic on a new line on the screen.



Creating a Java ApplicationUsing GUI Output

• JOptionPane (import javax.swing.JOptionPane;)– Produce dialog boxes

• Dialog box – GUI object resembling window– Messages placed for display

• Package– Group of classes

• The import statement– Use to access built-in Java class


Creating Java Application Using GUI Output

• TASK:

• Modify your “Hello, world!” program to a program that displays your name, your e-mail address and your postal address, each topic on a new output message dialog box.


Creating a Java Application Using GUI Output

import javax.swing.JOptionPane; public class FirstDialog

{

public static void main(String[] args)

{

JOptionPane.showMessageDialog(null,”First Java dialog");

}

}


Correcting Errors and Finding Help

• First line of error message displays:– Name of file where error found– Line number– Nature of error

• Next lines identify:– Symbol – Location

• Compile-time error– Compiler detects violation of rules – Refuses to translate class to byte code.


Correcting Errors andFinding Help (continued)

• Parsing – Process compiler uses to divide source code into

meaningful portions

• Logic error– Syntax correct but produces incorrect results when

executed– Usually more difficult to find and resolve

• Java API – Also called the Java class library– Prewritten Java classes


You Do It – training session

• Your first application– Compile and run file First.java– Compile and run file FirstDialog.java (for more

details see next slide)– Try to compile and run file ErrorTest.java

• Adding comments to a class

• Modifying a class


You Do It – training session

• Creating a dialog box– Compile and run file FirstDialog.java– Modify program to produce two dialog boxes

• JOptionPane.showMessageDialog(null, "First Java dialog");

• JOptionPane.showMessageDialog(null, "Second Java dialog");

– Modify program to produce three dialog boxes• JOptionPane.showMessageDialog(null, "First Java dialog");

• JOptionPane.showMessageDialog(null, "Second Java dialog");

• JOptionPane var = new JOptionPane();var.showMessageDialog(null, "Third Java dialog");

67

The jar utilitypp 68-80

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What is JAR?Java archive file can be used to group all the project files in a compressed file for deployment.

The Java archive file format (JAR) is based on the popular ZIP file format.

69

The jar utility JAR stands for Java ARchiver and it is used to

compress and archive one or more files. It is equivalent to Zip file in Window OS. A typical .jar file contains Java class files in addition to source files as well as resource files, like images and properties. Let us see how to create

A regular Java archive (.jar) file and A self-Executable Java archive file. An archive self

executable file is nothing but a .jar file along with a manifest info containing the entry point of the Application specified in the form of class name.

For example, consider the following Java source files.

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The jar utility – regular archive file// File prog44.java:

import java.util.Scanner;

public class prog44 {

public static void main(String[] args) {

int a, b, c;

Scanner cin = new Scanner(System.in);

System.out.println("Enter two integers:");

a = cin.nextInt(); b = cin.nextInt(); c = a + b;

System.out.println("Result is = " + c);

System.out.println("Factoriel of result is " + factr(c));

}

static int factr(int n) {

if (n==0) return 1;

else return n*factr(n-1);

}

}

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The jar utility We must build the corresponding .class file using

javac compiler. javac prog44.java

This is the only class and it contains the main() method

Now, let us see how to create the regular jar comprising the above class. Java utility called jar.exe contains options for creating, listing, updating the jar file.

Q:\>jar cvf prog44.jar prog44.class In the above command, the options can be interpreted

as follows, c - to create the archive file v – to give verbose output during the jar file creation f – the name of the jar file, ‘prog44.jar'

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The jar utilitySome more options: t – list table of contents for archivex – extract named (or all) files from archive

To list the contents of archive file, type command:

Q:\>jar tf prog44.jar

To extract files from archive, type command:Q:\>jar xf prog44.jar

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The jar utilityNow to list down the contents of

the jar file, we have to use the 't' option along with 'v' and 'f' options,

Q:/>jar tvf prog44.jar

The above command will list down the contents of prog44.jar (including directories and files).

74

Viewing the Contents of a JAR File

You can view the contents of a .jar file using WinZip.

75

The jar utilityTo extract the contents of

a .jar file to the current working directory, we can use the 'x' option as used in the following command,

Q:\>jar xvf prog44.jar

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The jar utility- self executable archive file

File ProgGeometricObject.java: We must build the corresponding .class file(s)

using javac compiler. javac ProgGeometricObject.java

There are four .class files generated by the compiler:

Circle.class GeometricObject.class ProgGeometricObject.class – (includes main() method) Rectangle.class

Now, let us see how to create the self executable jar comprising the above classes. When we invoke jar, we must point the entry point of the application using another option

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jar utility- self executable archive filee – specify application entry point for

stand-alone application bundled in executable .jar file

To create self executable .jar file, type the command:

Q:\>jar cvfe Archive2.jar ProgGeometricObject *.class

To create regular .jar file, type command:Q:\>jar cvf Archive1.jar *.classCompare both Archive1 and Archive2 .jar files

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The jar utility- self executable archive fileTo run self executable .jar file,

application we have to specify the '-jar' option like this command

Q:\>java –jar Archive2.jar

OR First: extract files andSecond: run JVMQ:\>jar xf Archive2.jarQ:\>java ProgGeometricObject

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The jar utility- self executable archive fileTo run self executable .jar file, type

commandQ:\>java –jar Archive1.jar

No successArchive1.jar has no specified entry point and therefore cannot consider it as self-executable archive file.

80

Practical session 5 Write a Java program to read a positive integer

value n and to display: The first n elements of the Fibonacci series Save the source texts as Prog55.java Build the corresponding .class file using javac

compiler. javac prog55.java

Run the program using java prog55

Build an archive file using jar utility. jar cvf prog55.jar prog55.class

Run the program through the archive file java –jar prog55.jar

Thank You For

Your Attention!

Any Questions?

INF120 Basics in JAVA Programming AUBG, COS dept Lecture 03 Title: Building Java programs using...

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