Welcome to java
Werbung
Welcome to java
einfach
● objektorientiert
● verteilt
● interpretierend
● robust
● secure
● architekturneutral
● portabel
● schnell
● parallel(multitheded)
●
1
Vielfalt von Java-Anwendungen
Android
AndroidApp
App
Java
Java
Applikation
Applikation
Applet
Applet
Desktopapplikation
Desktopapplikation
mit
mitGUI
GUI(AWT/Swing)
(AWT/Swing)
Applikationsserver
Applikationsserver
(ohne
(ohneUI)
UI)
JavaBeans
JavaBeans
(Javaenterprise)
(Javaenterprise)
Servlet
Servlet
Konsolapplikation
Konsolapplikation(ohne
(ohneGUI)
GUI)
JavaFX
JavaFXApplikation
Applikation
2
Erstes Java-Programm
Dateiname: Klassenname.java
Indiesem Fall:
HelloOne.java
public
public class
class HelloOne
HelloOne
{{
public
public static
static void
void main(String
main(String args[])
args[])
{{
System.out.println("welcome
System.out.println("welcome to
to java");
java");
System.out.println("today
System.out.println("today is
is "+new
"+new
java.util.Date());
java.util.Date());
}}
}}
3
Kommandozeilenargumente
public
public class
class HelloEcho
HelloEcho
{{
public
public static
static void
void main(String
main(String args[])
args[])
{{
for(int
for(int i=0;i<args.length;i++)
i=0;i<args.length;i++)
System.out.println(args[i]);
System.out.println(args[i]);
//
// oder
oder
for(String
for(String s:args)
s:args)
System.out.println(s);
System.out.println(s);
System.exit(0);
System.exit(0);
}}
}}
4
Mit Graphic User Interface (AWT)
import
import java.awt.*;
java.awt.*;
import
import java.awt.event.*;
java.awt.event.*;
import
import java.util.*;
java.util.*;
public
public class
class HelloTwo
HelloTwo extends
extends Panel
Panel
{{
Label
Label l1=new
l1=new Label("welcome
Label("welcome to
to java",Label.CENTER);
java",Label.CENTER);
Label
Label l2=new
l2=new Label("today
Label("today is
is "+new
"+new
Date(),Label.CENTER);
Date(),Label.CENTER);
Button
Button close=new
close=new Button("Close");
Button("Close");
}}
public
public HelloTwo()
HelloTwo()
{{
.. .. ..
}}
public
public static
static void
void main(String
main(String args[])
args[])
{{
.. .. ..
}}
5
Der Constructor
public
public HelloTwo()
HelloTwo()
{{
setFont(new
setFont(new Font("System",
Font("System", Font.PLAIN,24));
Font.PLAIN,24));
setLayout(new
setLayout(new GridLayout(3,1,0,10));
GridLayout(3,1,0,10));
add(l1);
add(l1);
add(l2);
add(l2);
add(close);
add(close);
close.addActionListener(new
close.addActionListener(new ActionListener()
ActionListener()
{public
{public void
void actionPerformed(ActionEvent
actionPerformed(ActionEvent e)
e)
{System.exit(0);}});
{System.exit(0);}});
}}
Hier entsteht eine inner class,
in diesem Fall eine anonomous class
6
Die main-Function
public
publicstatic
staticvoid
voidmain(String
main(Stringargs[])
args[])
{{
Frame
Framef=new
f=newFrame("first
Frame("firstDesktop
DesktopApplication");
Application");
HelloTwo
HelloTwohh=new
=newHelloTwo();
HelloTwo();
f.add(h);
f.add(h);
f.setVisible(true);
f.setVisible(true);
f.pack();
f.pack();
}}
7
Das Applet
import
import java.applet.*;
java.applet.*;
import
import java.awt.*;
java.awt.*;
public
public class
class HelloThree
HelloThree extends
extends Applet
Applet
{{
public
public void
void init()
init()
{{
Panel
Panel h=new
h=new HelloTwo();
HelloTwo();
add(h);
add(h);
}}
Ein Applet wird immer in eine html-Seite
}}
eingebunden und mittels Browser
oder appletviewer ausgeführt.
<html>
<html>
<body>
<body>
<applet
<appletcode=HelloThree
code=HelloThreewidth=940
width=940height=540></applet>
height=540></applet>
</body>
</body>
</html>
</html>
8
Verbesserte Version:
public
publicclass
classHelloTwoBetter
HelloTwoBetterextends
extendsPanel
Panel
{{
Label
Labell1=new
l1=newLabel("welcome
Label("welcometotojava",Label.CENTER);
java",Label.CENTER);
Label
l2=new
Label("today
is
"+new
Label l2=new Label("today is "+newDate(),Label.CENTER);
Date(),Label.CENTER);
public
publicHelloTwoBetter()
HelloTwoBetter()
{{
setFont(new
setFont(newFont("System",
Font("System",Font.PLAIN,24));
Font.PLAIN,24));
setLayout(new
GridLayout(3,1,0,10));
setLayout(new GridLayout(3,1,0,10));
Button ist hier in der main-fkt.
add(l1);
add(l1);
Somit taucht er bei Verwendung
add(l2);
add(l2);
}}
Des Panels als Component im
Applet nicht mehr auf
public
publicstatic
staticvoid
voidmain(String
main(Stringargs[])
args[])
{{
Frame
Framef=new
f=newFrame("first
Frame("firstDesktop
DesktopApplication");
Application");
HelloTwoBetter
h
=new
HelloTwoBetter();
HelloTwoBetter h =new HelloTwoBetter();
f.add(h,BorderLayout.CENTER);
f.add(h,BorderLayout.CENTER);
Button
Buttonclose=new
close=newButton("Close");
Button("Close");
close.addActionListener(new
close.addActionListener(newActionListener()
ActionListener()
{public
void
actionPerformed(ActionEvent
{public void actionPerformed(ActionEvente){System.exit(0);}});
e){System.exit(0);}});
f.add(close,BorderLayout.SOUTH);
f.add(close,BorderLayout.SOUTH);
f.setVisible(true);
f.setVisible(true);
f.pack();
f.pack();
}}
}}
9