2 2 java start jumpstart

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Table of Contents

LESSON: Java Jumpstart.................................................................................................................................1

Subjects................................................................................................................................................................2

Java Applications and Applets..........................................................................................................................3

Java Application − Edit......................................................................................................................................4

Java Application − Compile...............................................................................................................................5

Java Application − Run......................................................................................................................................6

Anatomy − Declaring a class..............................................................................................................................7

Anatomy − The main() method..........................................................................................................................8

Anatomy − Printing Output...............................................................................................................................9

Anatomy − Using Comments...........................................................................................................................10

Applet − Edit.....................................................................................................................................................11

Applet − Compile..............................................................................................................................................12

Applet − Embed in HTML Page......................................................................................................................13

Applet − Run (Browser)...................................................................................................................................14

Applet − Run (Browser) Result.......................................................................................................................15

Applet − Run (appletviewer)............................................................................................................................16

Anatomy − Extend from java.applet.Applet..................................................................................................17

Anatomy − paint() method...............................................................................................................................18

Anatomy − drawString()..................................................................................................................................19

Anatomy − Importing Classes..........................................................................................................................20

LABS.....................................................................................................................................................20

1. HelloWorld Application..............................................................................................................20

2. Using CLASSPATH and packages.............................................................................................20

3. Using System Input/Output.........................................................................................................21

4. Using command line parameters.................................................................................................21

RESOURCES....................................................................................................................................................23

i



LESSON: Java Jumpstart

author: Just van den Broecke − [email protected]

organization: Just Objects B.V. − www.justobjects.nl

Slides

Subjects1.

Java Applications and Applets2.

Java Application − Edit3.

Java Application − Compile4.

Java Application − Run5.

Anatomy − Declaring a class6.

Anatomy − The main() method7.

Anatomy − Printing Output8.

Anatomy − Using Comments9.

Applet − Edit10.

Applet − Compile11.

Applet − Embed in HTML Page12.

Applet − Run (Browser)13.

Applet − Run (Browser) Result14.

Applet − Run (appletviewer)15.

Anatomy − Extend from java.applet.Applet16.

Anatomy − paint() method17.

Anatomy − drawString()18.

Anatomy − Importing Classes19.

Labs

HelloWorld Application1.

Using CLASSPATH and packages2.

Using System Input/Output3.

Using command line parameters4.

Resources

1



Subjects

Two ways to write and execute a Java Program•

Java Applications

writing, compiling, running a Java Application♦

anatomy of a java program♦

•

Java Applets

writing, compiling, running an Java Applet♦

anatomy of a Java Applet♦

•

Java Jumpstart 1

2



Java Applications and Applets

Java programs can be written and executed in two ways

Java Applications: stand−alone, command line applications1.

Java Applets: run under control of a Java−capable browser2.

We will learn how to edit/compile/run each of these

Java Jumpstart 2

3



Java Application − Edit

1: // Demonstrates the most basic Java Application.

2: public class HelloProgram {

3:

4: public static void main (String [] args) {

5: System.out.println ("Hello World");6: }

7: }

take a text editor•

write the above program•

save the program as HelloProgram.java•

Java Jumpstart 3

4



Java Application − Compile

Enter the commandline:

javac HelloProgram.java

Java Jumpstart 4

5



Java Application − Run

Enter the commandline:

java HelloProgram

Observe "Hello World" printed on the console.

Java Jumpstart 5

6



Anatomy − Declaring a class

Declaring a class

public class HelloProgram {

...}



3:


5: System.out.println ("Hello World");

6: }

7: }

Java Jumpstart 6

7



Anatomy − The main() method

public static void main(String[] args) {

...

}

A Java application should define a main() method•

Entry for start of execution•

Optional command−line arguments passed as array of String•

Java Jumpstart 7

8



Anatomy − Printing Output

Object System provides object out Object out

has print method println

...

System.out.println ("Hello World");

...



3:


5: System.out.println ("Hello World");

6: }

7: }

Java Jumpstart 8

9



Anatomy − Using Comments

1: // Comment type 1: HelloProgram.java

2:

3: /*

4: * This is comment type 2.

5: */6: public class HelloProgram {

7:

8: /** Comment type 3: Javadoc style comment. */


10: System.out.println ("Hello World"); // also type 1

11: }

12: }

13:

Java Jumpstart 9

10



Applet − Edit

1: // Demonstrates the most basic Java applet.

2: import java.applet.Applet;

3: import java.awt.Graphics;

4:

5: public class HelloApplet extends Applet {6:

7: public void paint (Graphics g) {

8: g.drawString ("Hello World", 50, 50);

9: }

10: }

take a text editor•

write the above applet•

save file as HelloApplet.java•

Java Jumpstart 10

11



Applet − Compile

The same as with Java Application

Enter on a commandline:

javac HelloApplet.java

Java Jumpstart 11

12



Applet − Embed in HTML Page

1: <html>

2:

3: <head>

4: <title>HelloApplet html file</title>

5: </head>6:

7: <body>

8: <h1>HelloApplet html file</h1>

9:

10: <applet code="HelloApplet.class" height="100" width="200">

11: </applet>

12:

13: </body>

14: </html>

Applet requires browser•

Applet is part of an HTML page•

You have to write a HTML page•

Save as HelloApplet.html•

Java Jumpstart 12

13



Applet − Run (Browser)

start browser•

select HelloApplet.html•

Java Jumpstart 13

14



Applet − Run (Browser) Result

Java Jumpstart 14

15



Applet − Run (appletviewer)

Another way to run an Applet•

Advantage: no caching•

Disadvantage: only shows applet and not the rest of the HTML page•

Enter commandline:

appletviewer HelloApplet.html

Java Jumpstart 15

16



Anatomy − Extend from java.applet.Applet




4:




9: }

10: }

Your applet should inherit from java.applet.Applet

Java Jumpstart 16

17



Anatomy − paint() method




4:




9: }

10: }

Overriding paint() method

public void paint(Graphics g) {

...

}

Java Jumpstart 17

18



Anatomy − drawString()




4:




9: }

10: }

Calling drawString()

...

g.drawString("Hello World", 50, 50);

...

Java Jumpstart 18

19



Anatomy − Importing Classes




4:




9: }

10: }

Use import statements to include library classes.

import java.applet.Applet;

import java.awt.Graphics;

...

Java Jumpstart 19

LABS

1. HelloWorld Application

This lab is meant to make you familiar with the J2SE environment. by making the HelloWorld application.

Create HelloWorld.java with a text editor.1.

Compile HelloWorld.java with the "javac" command.2.

Run HelloWorld with the "java" command.3.

If you see something like

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld

set your CLASSPATH as follows:

set CLASSPATH=.;%CLASSPATH%

2. Using CLASSPATH and packages

This lab is meant to make you familiar with CLASSPATH and packages.

Copy the HelloWorld.java from the previous lab.1.

Be sure your CLASSPATH is set as in the previous lab. Add as the first line of HelloWorld.java the

following:

package mypackage;

2.

Recompile.3.

Run the HelloWorld program by typing "java HelloWorld". What do you observe ?4.

Run the HelloWorld program by typing "java mypackage/HelloWorld". What do you observe ?5.

Run the HelloWorld program by typing "java mypackage.HelloWorld". What do you observe ?6.

Make a subdirectory 'mypackage' and move HelloWorld.class to that directory.7.

Run the HelloWorld program by typing "java mypackage/HelloWorld". What do you observe ?8.


20



Delete HelloWorld.class from the mypackage subdir.10.

Make a subdirectory 'myclasses'.11.

Compile HelloWorld.java with

javac −d myclasses HelloWorld.java

.

12.

Where is the HelloWorld.class now located ?13.


Adapt the CLASSPATH by typing

set CLASSPATH=myclasses;%CLASSPATH%

15.


3. Using System Input/Output

This lab is meant to introduce System.in and System.out. Input/output will be treated in more depth in

subsequent lessons. Make a program that reads an int from the input and prints it to the output.

Use the following skeleton code (copy from the lab3 subdir).1: /**

2: * Echo input to output.

3: * <p>

4: * core/jumpstart/lab3

5: * <p>

6: * $Id: EchoInput.java,v 1.2 2004/03/14 15:42:43 justb Exp $

7: * <p>

8: *

9: * @author $Author: justb $ − Just van den Broecke − Just Objects ©

10: */

11:

12: public class EchoInput {

13:14: public static void main (String [] args) throws java.io.IOException {

15: int i = 0;

16:

17: <YOUR CODE HERE>

18:

19: System.out.println ("you typed "+i);

20: }

21: }

1.

Add a line that reads the int from the standard input (keyboard) using i = System.in.read()2.

Compile and run.3.

Type a number. What do you observe ? (Hint: what about bytes?)4.

4. Using command line parameters

This lab is meant to make you familiar with the commandline parameters.

Make a program Echo.java that echoes its commandline parameters to the standard output.

Hints:

You will need a "for" loop. The general structure in Java is

for (int i=0; i < N; i++) {

// do something;

}

•

21



You may want to skip ahead to the Control Flow lesson.

You will need the size (N) of the args−array. This is provided by args.length.•

22



RESOURCES

[javasoft−5−2] JavaSoft ; The Java Tutorial − Trail: Getting Started ; From the Java Tutorial. Contains

detailed instructions for compiling and running your first program.

http://www.javasoft.com/docs/books/tutorial/getStarted/TOC.html

[baldwin−010] Richard G. Baldwin ; Hello World ; This lesson introduces you to Java programming by

presenting and discussing some different versions of the Hello World program.

http://www.dick baldwin.com/java/Java010.htm

[baldwin−012] Richard G. Baldwin ; Defining a Class ;


[baldwin−014] Richard G. Baldwin ; The main() Method ;


[baldwin−016] Richard G. Baldwin ; Using the System and PrintStream Classes ;


[baldwin−017] Richard G. Baldwin ; Introduction to Graphical User Interfaces (GUI) ;


[baldwin−018] Richard G. Baldwin ; Introduction to Applets ;


[baldwin−032] Richard G. Baldwin ; Command−Line Arguments ;


[baldwin−052] Richard G. Baldwin ; Setting Program Attributes ;


[baldwin−054] Richard G. Baldwin ; Using System Resources ;

http://www.dickbaldwin.com/java/Java054.htm


















http://www.javasoft.com/docs/books/tutorial/getStarted/TOC.html

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