carnegie mellon university, graduate school of industrial administration 1 event handling inner...

Carnegie Mellon University, Graduate School of Industrial Administration

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• Event Handling• Inner classes• Event Handling and Inner Classes • GUI Programming• Threads and Web Servers

Week Four


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Event Handling

• Used by the Abstract Window Toolkit (AWT) – for basic GUI programming Java 1.0• Used by Swing -- Better components than AWT Java 2• Used by JavaBeans -- reusable software components, like Visual Basic, that can be manipulated in a builder tool


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Babysitting

A baby in the home needs attention.Many events surrounding the baby are not easily ignored.Events can be of different types.


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One possible source of events


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Babysitting

Before responding to an event, a babysitter typically takes noteof the source and the type of event.


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Babysitting

The sitter needs to know both the event type and the event source.

Event source

Event type

Handler


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Event Handling

The window manager software may generate hundreds of differentevents.

Examples include mouse clicks, mouse movements, key strokes,and timer ticks.

A programmer is typically interested in a small subset of all of the possible events that may occur.


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Events and Event Objects

• Since events may be of different types but still exhibit some shared traits (inheritance) Java represents the event classes in a hierarchy.

• The root class is called java.util.EventObject. The only common feature shared by all events is a source object. So we find the following method in the EventObject class :

public Object getSource();


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EventObject

AWTEvent

ActionEvent ComponentEvent

InputEvent WindowEvent

MouseEvent KeyEvent

Some classes andmethods in the eventhierarchy.

Object

String getActionCommand()

int getX()char getKeyChar()

boolean isAltDown() Window getWindow()


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Event handling usually involves three types of objects

• Objects are used to hold and report on information about the event.• Objects are typically the source of events.• Objects, called listeners, are used to handle events.


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ExampleA mouseobject

A mouseobject

An event object that describes, say, the x and y coordinate of where the mouse was clicked


The listener object has methods that are called for particular events


Event Source

Event data and methods

Listener


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ExampleA mouseobject

A mouseobject





ImplementsMouseListener

The event object is sentto a listener method

A mouse object mustbe told who its listener is.


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The Listener

There are different types of Listeners.

MouseListenersWindowListenersScrollBarListenersEtc..

These Listeners are interfaces. Remember what an interfaceprovides? If class X implements an interface then class X promisesto provide (at least) the methods declared in the interface.


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Some of the Listener Hierarchy

EventListener

ActionListener

abstract void actionPerformed(ActionEvent e);

MouseListener

abstract void mouseClicked(MouseEvent e)

KeyListener


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A Listener Interface

public interface MouseListener {

void mouseClicked(MouseEvent e); void mouseEntered(MouseEvent e); void mouseExited(MouseEvent e); void mouseReleased(MouseEvent e);

}

//What does it mean if I claim that I implement this interface?


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An Example

// MouseSpyApplet.java

import java.applet.Applet;import java.awt.event.MouseEvent;import java.awt.event.MouseListener;


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class MouseSpy implements MouseListener{ public void mouseClicked(MouseEvent event) { System.out.println("Mouse clicked. x = " + event.getX() + " y = " + event.getY()); } public void mouseEntered(MouseEvent event) { System.out.println("Mouse entered. x = " + event.getX() + " y = " + event.getY()); } public void mouseExited(MouseEvent event) { System.out.println("Mouse exited. x = " + event.getX() + " y = " + event.getY()); } public void mousePressed(MouseEvent event) { System.out.println("Mouse pressed. x = " + event.getX() + " y = " + event.getY()); } public void mouseReleased(MouseEvent event) { System.out.println("Mouse released. x = " + event.getX() + " y = " + event.getY()); }}

I have to provideALL of these methods!!


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public class MouseSpyApplet extends Applet{ public MouseSpyApplet() { MouseSpy listener = new MouseSpy(); addMouseListener(listener); }}


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<html><head></body></head><B>Spying on the mouse</b><p><applet code="MouseSpyApplet.class" width=400 height=200></applet>

</html>

Java Applets need an HTML file.


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Another approachSuppose a friendly sole created this class:

public class MouseAdapter implements MouseListener { void mouseClicked(MouseEvent e){} void mouseEntered(MouseEvent e){} void mouseExited(MouseEvent e){} void mouseReleased(MouseEvent e){}}

Now, suppose I extend this class. What must I provide?


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Only those methods that I am interested in.

The other methods, when called, do nothing. We’ll visit this issue again later.


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Inner Classes

• Nested Top Level Classes (not inner)

• Member Classes

• Local Classes

• Anonymous Classes


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Nested Top Level Class

• Nested top-level classes are not inner classes.• Use as a convenient way to group related classes• Since the class must be static and has no 'this' pointer, it has no access to the instance data of objects for its enclosing class.• It behaves just like a 'normal' class or interface.


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//NestedTopLevelExample.java

class Top { int i,j; static class SomeClass { // static makes it top-level nested int k; SomeClass() { System.out.println("Constructing SomeClass"); } void foo() { System.out.println("Hello"); } } Top() { System.out.println("Constructing a Top object"); }

}


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public class NestedTopLevelExample {

public static void main(String args[]) {

Top myTop = new Top();

Top.SomeClass myObject = new Top.SomeClass(); myObject.foo(); }}

Output

Constructing a Top objectConstructing SomeClassHello


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Member Classes

• Member classes (there is no such thing as a 'member‘ interface)• This inner class (it's not a top-level class) has no static keyword and can access the members of each object of its outer class.• The class 'appears in every instance'.•


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•The parent class must declare an instance of an inner class, before it can invoke the inner class methods, assign to data fields (including private ones), and so on.•Unlike nested top-level classes, inner classes are not directly part of a package and are not visible outside the class in which they are nested.• Inner classes are often used for GUI event handlers.


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// MemberClassExample.javaclass Top { int i = 33; public class SomeClass { // access the outer object's state. private int k = i; SomeClass() { System.out.println("Constructing SomeClass"); } void foo() { System.out.println("Hello"); } } Top() { System.out.println("Constructing a Top object"); SomeClass sc = new SomeClass(); System.out.println(sc.k); }}


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public class MemberClassExample {


Top myObject = new Top(); }}

// OUTPUTConstructing a Top objectConstructing SomeClass33


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Local Classes

•A Local class is an inner class. Typically, a local class is declared within a method. It is not a member of an enclosing class. It is visible only within the block.

•These classes are used primarily as "adapter classes".

• For example, a block of code that creates a Button object could use a local class to define a simple implementation of the ActionListener Interface. Then it could instantiate this simple implementation and pass the resulting object to the button's ActionListener method, thereby connecting the button to the "callback" code that is executed when the button is pressed.


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// Local Class exampleclass Top { int i = 33; Top() { System.out.println("Constructing a Top object"); // define a class within a method class Wow { int t; Wow() { System.out.println("Building a Wow"); i = 8; t = 9; } } Wow h = new Wow(); System.out.println(" h.t == " + h.t); System.out.println(" i == " + i); }}


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public class LocalExample {


Top myObject = new Top(); }}

// OUTPUT

Constructing a Top objectBuilding a Wow h.t == 9 i == 8


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• An anonymous class is refinement of inner classes.• It allows you to combine the definition of the class with the instance allocation.• Since it is instantiated in the same expression that defines it, it can only be instantiated once. This is very similar to local classes. • When writing a simple adapter class, the choice between a named local class and an unnamed anonymous class typically comes down to a matter of style and code clarity, rather than any difference in functionality.•The new class can't have a constructor.

Anonymous Classes


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// Anonymous.java

interface SmallClass { public void foo();}

class Top { int i = 33; void someMethod(SmallClass s) { s.foo(); } void anotherMethod() { someMethod(new SmallClass() { public void foo() { System.out.println("Really fun"); } }); }


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Top() { System.out.println("Constructing a Top object"); someMethod(new SmallClass() { public void foo() { System.out.println("Strange but fun"); } }); }}


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public class Anonymous {


// We can't create interface objects // error: SmallClass s = new SmallClass();

Top myObject = new Top(); myObject.anotherMethod(); }}// OUTPUTConstructing a Top objectStrange but funReally fun


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Event Handling and Inner Classes

register Source Object Listener Object

fire events

After the listener object registers itself with the sourceobject, the source object calls a method found in thelistener object and passes an object that describes the event.

Event object


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Event Handling

Suppose we have a Button object Button b = new Button();

We must determine what events a particular component generates.

A Button component may generate an ActionEvent object.

Button b

ActionEventObject

ActionEventObject


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Implementing a Listener

class BabySitter implements ActionListener { public void actionPerformed(ActionEvent e) { // handle the event object e in some way }}

•We need an object that will listen for the ActionEvent.•We implement the ActionListener class (this class listens for ActionEvents from buttons, menus, etc.) and override its actionPerformed method.


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Create a BabySitter object

BabySitter sitter = new BabySitter();

sitter


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Registering The Listener

• We want to listen for the ActionEvent object coming from the button.

• So, we tell the button what object will listen for the ActionEvent object:

• b.addActionListener(sitter)


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The button and its listener

Button Object Sitter Object

The button calls the actionPerformed()method of the sitter objectand passes an ActionEvent objectas a parameter

addActionListener


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Hit the X and the program exits

Once again but with a window


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Create a WindowCloseSitter Class

import javax.swing.*;import java.awt.event.*;

public class CloseDemo { public static void main(String[] args) { JFrame f = new JFrame("Example"); f.setSize(400,100); f.setVisible(true); WindowCloseSitter h = new WindowCloseSitter(); f.addWindowListener(h); }}


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class WindowCloseSitter implements WindowListener {

public void windowClosing(WindowEvent e) { System.exit(0); } public void windowClosed(WindowEvent e) { } public void windowOpened(WindowEvent e) { } public void windowIconified(WindowEvent e) { } public void windowDeiconified(WindowEvent e) { } public void windowActivated(WindowEvent e) { } public void windowDeactivated(WindowEvent e) { }

}

But we have to implement ALL of the functions !!


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Java Provides Adapter Classes

• ComponentAdapter• MouseMotionAdapter• WidowAdapter• ContainerAdapter• MouseAdapter• FocusAdapter• KeyAdapter


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The WindowAdapter class

public abstract class WindowAdapter implements WindowListener {

public void windowClosing(WindowEvent e) {} public void windowClosed(WindowEvent e) { } public void windowOpened(WindowEvent e) { } public void windowIconified(WindowEvent e) { } public void windowDeiconified(WindowEvent e) { } public void windowActivated(WindowEvent e) { } public void windowDeactivated(WindowEvent e) { }}

A built in class -- we already have the empty bodies!!


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The Window again

import javax.swing.*;import java.awt.event.*;public class CloseDemo2 extends WindowAdapter { public static void main(String[] args) { JFrame f = new JFrame("Example"); f.setSize(400,100); f.setVisible(true); f.addWindowListener(new CloseDemo2()); } public void windowClosing(WindowEvent e) { System.exit(0); }}


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Again with anonymous classes

import javax.swing.*;import java.awt.event.*;public class CloseDemo3 { public static void main(String[] args) { JFrame f = new JFrame("Example"); f.setSize(400,100); f.setVisible(true); f.addWindowListener( new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } } ); } }


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Java GUI programming and Java Threads

GUI example taken from “Computing Concepts with Java 2” byCay Horstmann

Thread examples taken from “The Java Programming Language”By Arnold and Gosling and from Cay Horstmann’s “Core Java 2 Advanced”

GUI Programming with threads


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Frame Windows

A Frame window has a border and a title bar

A Frame window has an addWindowListener method. We canuse this method to add listeners to our frame window.


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An example

import javax.swing.*;import java.awt.event.*;

public class InternetFrameExample {

public static void main(String[] args) {

JFrame f = new InternetFrame("Example"); f.setTitle("Internet browser"); f.show(); }}

javax means Java standardextension

Tell the window manager todisplay the frame.


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class InternetFrame extends JFrame {

public InternetFrame(String s){

setSize(300,300); WindowCloser listener = new WindowCloser(); addWindowListener(listener); }

private class WindowCloser extends WindowAdapter {

public void windowClosing(WindowEvent e) { System.exit(0); } } }

windowOpened()widowClosed()windowClosing() : :

Add the handler


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Adding User Interface Components to a Frame

•Do not draw directly on the surface of a frame.•Frames have been designed to arrange user interface components.•User interface components are such things as buttons, menus, scroll bars, and so on.•If you want to draw on a frame, draw on a separate component and then add that component to the frame. The Swing UI toolkit provides the Jpanel class for this purpose.


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Drawing on a JPanel

To draw on a Jpanel you override the paintComponent method.

Make sure that from within your paintComponent method youcall super.paintComponent(…) so that the superclass method paintComponent has a chance to erase the existing contents,redraw the borders and decorations, etc.


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Adding the Panel to the JFrame

• The surface of a Swing frame is covered with four panes.

• Each of these four has a purpose.• We are interested in getting access to the JFrame’s content pane.• So, call the getContentPane on the JFrame.• This call returns a Container object.• Add your Panel object to the content pane

Container.


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Adding a Panel to a JFrame

x = getContentPane (a contentPane holdscomponents for display).

x refers to a Container (may contain other components)

c = a Panel or some other component.

Add c to x using x’s layoutmanager (a content pane usesborder layout)

JFrame

getContentPane()


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Adding a JTextfield to the JFrame

JFrame

getContentPane()

class MyFrame extends JFRAME { private JTextField textField; public MyFrame() { Container cp = getContentPane();

textField = new JTextField();

cp.add(textField, “South”);

cp


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We may want to add a listener to the TextField

JFrame

getContentPane()

Class MyFrame extends JFRAME { private JTextField textField; public myFrame() { Container cp = getContentPane();

textField = new JTextField();

cp.add(textField, “South”);

textField.addActionListener( new TextFieldListener());

cp


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Output first! -- user enters number of eggs and we draw them


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Strategy

Think about • What do we want on the screen?• What events should we listen for?• What should we do when those events occur?• What processing will we do when user input arrives?• What object has responsibilities for what activities?

Think about

• The ‘has-a’ relationship,e.g., the Jframe’s ContentPane “has-a” Panel and a TextField.• The ‘is-a’ relationship,e.g., The TextFieldListener ‘is-an’ actionListener.


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// Example// Eggs.java

import java.awt.Container;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;import java.awt.geom.Ellipse2D;import java.util.Random;import javax.swing.JFrame;import javax.swing.JPanel;import javax.swing.JTextField;

We need classes fromthe awt, util, and swingpackages.


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public class Eggs{ public static void main(String[] args) { EggFrame frame = new EggFrame(); frame.setTitle("Enter number of eggs"); frame.show(); }}

This thread is doneafter creating a frame andstarting up the frame thread.

A frame now exists and is running.


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The EggFrame Constructor

• Set the size of the frame• Add a listener to listen for the stop event• Create a JPanel object to draw on and a

JTextField object to interact with the user via the keyboard

• Add a listener for the JTextField• Add the Jpanel and the JTextField to the contentPane container.


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class EggFrame extends JFrame{ private JTextField textField; private EggPanel panel;

public EggFrame() { final int DEFAULT_FRAME_WIDTH = 300; final int DEFAULT_FRAME_HEIGHT = 300; setSize(DEFAULT_FRAME_WIDTH, DEFAULT_FRAME_HEIGHT);

addWindowListener(new WindowCloser()); panel = new EggPanel(); textField = new JTextField(); textField.addActionListener(new TextFieldListener()); Container contentPane = getContentPane(); contentPane.add(panel, "Center"); contentPane.add(textField, "South"); }

A listener for the jframewindow

A textField listener

As before


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The constructor will be called from our main thread.

The other thread operates asynchronously.

What do we mean by asynchronous execution?

Who is running the show?

Don’t programs run sequentially?

We have to think differently.

Event driven programming


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The TextField

The TextField object will call us when it detectsan event.

We don’t ‘read the input’. We set up a babysitter torespond.

The TextField object sends us an event object.


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// Use an inner class to listen on the text field

private class TextFieldListener implements ActionListener { public void actionPerformed(ActionEvent event) { String input = textField.getText(); panel.setEggCount(Integer.parseInt(input)); textField.setText(""); } } We do two things when we

have a textfield event.1) Get the data2) Tell the panel the number of eggs to display


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// Use an inner class to listen on the text field

private class TextFieldListener implements ActionListener { public void actionPerformed(ActionEvent event) { String input = textField.getText(); panel.setEggCount(Integer.parseInt(input)); textField.setText(""); } } Note how handy the inner class is. Both panel and

textField are available. What if the listener were notan object of an inner class. how would it get accessto these variables? We can’t just pass the variables onthe call because we don’t make the call.


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private class WindowCloser extends WindowAdapter { public void windowClosing(WindowEvent event) { System.exit(0); } }}

This is how we respond when theclose signal is received.system.exit(0) stops the java virtual machine. 0 means normal termination.


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How about the panel object

What are the panel object’s responsibilities?

get input? _____ repaint itself? _____ keep track of the egg count? _____ hold the data it needs to repaint itself? _____

Do we want our panel to inherit properties and methods from anyexisting classes? _____


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What are the panel object’s responsibilities?

get input? No, that’s the TextField’s job. repaint itself? Sure, that’s its main job. keep track of the egg count? Yes, better here where it’s needed hold the data it needs to repaint itself? Yes

Do we want our panel to inherit properties from any existing classes? Sure, we want to re-use existing code whenever possible.


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When should the panel object repaint itself?

What will the panel need to repaint itself?

Who actually calls the paintComponent method?


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When should the panel object repaint itself? When a new input arrives from the user. When the egg count changes. What will the panel need to repaint itself? A graphics object to draw on.

Who actually calls the paintComponent method? While we have to provide a paintComponent method we don’t call it directly. It’s called by the Java run-time environment after we make a call on repaint.


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class EggPanel extends JPanel{

public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; // draw eggCount ellipses with random centers Random generator = new Random(); for (int i = 0; i < eggCount; i++) { double x = getWidth() * generator.nextDouble(); double y = getHeight() * generator.nextDouble(); Ellipse2D.Double egg = new Ellipse2D.Double(x, y, EGG_WIDTH, EGG_HEIGHT); g2.draw(egg); } }


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public void setEggCount(int count) { eggCount = count; repaint(); }

private int eggCount; private static final double EGG_WIDTH = 30; private static final double EGG_HEIGHT = 50;}


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Java Threads

• Four kinds of thread programming

• Applications– A GUI application– A server application


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Four kinds of thread programming

1) Unrelated threads

2) Related but unsynchronized threads

3) Mutually-exclusive threads

4) Communicating mutually-exclusive

threads

We will look at only the first two kinds.


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class Coffee extends Thread {

Coffee(String name) {super(name);

} public void run() {

for(int n = 1; n <= 3; n++) { System.out.println("I like coffee");

yield();System.out.println(this.getName());yield();

} }}

Unrelated threads


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class Tea extends Thread { Tea(String name) {

super(name); } public void run() { for(int n = 1; n <= 3; n++) {

System.out.println("I like tea");yield();System.out.println(this.getName());yield();

} }}


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public class Drinks {

public static void main(String args[]) { System.out.println("I am main");

Coffee t1 = new Coffee("Wawa Coffee");Tea t2 = new Tea(“Sleepy Time Tea");t1.start();t2.start();

System.out.println("Main is done");}

}


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I am mainMain is doneI like coffeeI like teaWawa CoffeeSleepy Time TeaI like coffeeI like teaWawa CoffeeSleepy Time TeaI like coffeeI like teaWawa CoffeeSleepy Time Tea

Output

Main finishes right away

Threads are sharing time

This program has three threads.


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• Using sleep() in unrelated threads

• The call sleep(millis) puts the currently executing thread to sleep for at least the specified number of milliseconds. "At least“ means there is no guarantee the thread will wake up in exactly the specified time. Other thread scheduling can interfere.

Unrelated Threads Part II


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class Coffee extends Thread {Coffee(String name) {

super(name);}public void run() {

for(int n = 1; n <= 3; n++) { System.out.println("I like coffee");

try { sleep(1000); // 1 second }

catch(InterruptedException e) {} System.out.println(this.getName());

}}

}


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class Tea extends Thread { Tea(String name) {

super(name);}

public void run() { for(int n = 1; n <= 5; n++) {

System.out.println("I like tea");System.out.println(getName());

}}

}


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public class Drinks2 { public static void main(String args[]) { System.out.println("I am main"); Coffee t1 = new Coffee("Wawa Coffee"); Tea t2 = new Tea("China Tea"); t1.start(); t2.start(); System.out.println("Main is done"); }}


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I am mainMain is doneI like coffeeI like teaChina TeaI like teaChina TeaI like teaChina TeaI like teaChina TeaI like teaChina TeaWawa CoffeeI like coffeeWawa CoffeeI like coffeeWawa Coffee

1 second pausing after each “I like coffee”

After “I like coffee”, the coffee thread goes to sleep and the tea thread gets to finish and die.


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Yield() and Sleep()

• Yield() may have no effect on some implementations.

• The thread scheduler might make no effort toward fairness.

• The yielding thread may be picked again even though other threads want a turn.

• It is a good idea to call sleep() instead.


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An Example Without Threads

Black ball bounces for awhile and then stops. If you then click start, a new ball bounces for awhile and then stops. Close only works between balls. If the ball is moving and you click close, the close message is queued.


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// From Cay Horstmann Core Java 2 Advancedimport java.awt.*;import java.awt.event.*;import javax.swing.*;

public class Bounce{ public static void main(String[] args) { JFrame frame = new BounceFrame(); frame.show(); }}


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class BounceFrame extends JFrame{ public BounceFrame() { setSize(300, 200); setTitle("Bounce");

addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } } );


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Container contentPane = getContentPane(); canvas = new JPanel(); contentPane.add(canvas, "Center"); JPanel p = new JPanel();

addButton(p, "Start", new ActionListener() { public void actionPerformed(ActionEvent evt) { Ball b = new Ball(canvas); b.bounce(); } });


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addButton(p, "Close", new ActionListener() { public void actionPerformed(ActionEvent evt) { System.exit(0); } }); contentPane.add(p, "South"); } public void addButton(Container c, String title, ActionListener a) { JButton b = new JButton(title); c.add(b); b.addActionListener(a); } private JPanel canvas;}


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class Ball{ public Ball(JPanel b) { box = b; }

public void draw() { Graphics g = box.getGraphics(); g.fillOval(x, y, XSIZE, YSIZE); g.dispose(); }


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public void move() { Graphics g = box.getGraphics(); g.setXORMode(box.getBackground()); g.fillOval(x, y, XSIZE, YSIZE); x += dx; y += dy; Dimension d = box.getSize(); if (x < 0) { x = 0; dx = -dx; } if (x + XSIZE >= d.width) { x = d.width - XSIZE; dx = -dx; } if (y < 0) { y = 0; dy = -dy; } if (y + YSIZE >= d.height) { y = d.height - YSIZE; dy = -dy; } g.fillOval(x, y, XSIZE, YSIZE); g.dispose(); }


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public void bounce() { draw(); for (int i = 1; i <= 1000; i++) { move(); try { Thread.sleep(5); } catch(InterruptedException e) {} } } private JPanel box; private static final int XSIZE = 10; private static final int YSIZE = 10; private int x = 0; private int y = 0; private int dx = 2; private int dy = 2;}


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Bouncing With Threads

The close button works in an instant. Each time the start button is clicked a new ball appears. The screen above shows four fast

moving bouncing balls.


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addButton(p, "Start", new ActionListener() { public void actionPerformed(ActionEvent evt) { Ball b = new Ball(canvas); b.start(); } });

We use start() rather than bounce() on the ball object…


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…and have the Ball class extend Thread and implement run() rather than bounce().

class Ball extends Thread:public void run() { try { draw(); for (int i = 1; i <= 1000; i++) { move(); sleep(5); } } catch(InterruptedException e) {} }


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Ping Pong

•Adapted from "The Java Programming Language", Arnold and Gosling•After a thread is created, you can configure it – set its name, its initial priority, and so on.•The start() method spawns a new thread of control based on the data in the thread object and then returns. Now, the •Java virtual machine invokes the new thread's run method, making the thread active.•When a thread's run method returns, the thread has exited.•The thread may be manipulated with a number of methods, including the interrupt() method as shown in this example.


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public class PingPong extends Thread {

private String word;private int delay;

public PingPong(String whatToSay, int delayTime) {word = whatToSay;delay = delayTime;

}


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public void run() { try {

for(;;) { System.out.println(word+" "); sleep(delay);

} } catch (InterruptedException e) { System.out.println("Interrupted!!!!!");

return; }}


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PingPong t1 = new PingPong("\tping",33); t1.start(); PingPong t2 = new PingPong("Pong",100); t2.start(); try { Thread.sleep(5000); } catch(InterruptedException e) {

// will not be printedSystem.out.println("Good morning");

return; }


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Thread myThread = Thread.currentThread(); for (int t = 1 ; t <= 10; t++) System.out.println("In Main..." + myThread.getName()); t1.interrupt(); }}


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C:\McCarthy\threads\PingPong>java PingPong pingPong ping ping pingPong ping ping pingPong ping ping ping : :

Main is asleep.

For 5 secondsping and pongtake turns sleepingand running


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Pong ping ping pingPongIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainIn Main...mainInterrupted!!!!!PongPongPongPongPong:

“Pongs” foreveror until until ctrl-c

Main wakes up

Main interruptsPing and ping dies.


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A Thread Application --A Simple Web Server

• Responds by sending the same file on each hit

• Creates a new thread on each hit


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// A simple web server// Responds with the same file on each hit

import java.net.*;import java.io.*;import java.util.*;

public class OneFile extends Thread {

static String theData = ""; static String contentType; static int contentLength; Socket theConnection;


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// construct each OneFile object with an existing socket public OneFile(Socket s) { theConnection = s; } // run the following code on each object public void run() { try { // get a PrintStream attached to this socket PrintStream os = new PrintStream( theConnection.getOutputStream()); // get a DataInputStream attached to this socket DataInputStream is = new DataInputStream( theConnection.getInputStream()); // read a line from the socket String request = is.readLine();


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// HTTP/1.0 and later send a MIME header if(request.indexOf("HTTP/") != -1) { // we need to read the rest of the MIME header while(true) { String thisLine = is.readLine(); if(thisLine.trim().equals("")) break; }

// respond to the client os.print("HTTP/1.0 200 OK\r\n"); // send the date Date now = new Date(); os.print("Date: " + now + "\r\n"); // send our name os.print("Server: OneFile 1.0\r\n");


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// send the contentLength os.print("Content-length: " + contentLength + "\r\n"); // send the content type os.print("Content-type: " + contentType + "\r\n\r\n"); }

// send the file in the string os.println(theData); theConnection.close(); } catch(IOException e) { } }


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// main loads the file and creates the object on every hit

public static void main(String args[] ) {

int thePort; ServerSocket ss; Socket theConnection; FileInputStream theFile;

// cache the file try { // open file and create a DataInputStream theFile = new FileInputStream(args[0]); DataInputStream dis = new DataInputStream(theFile);


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// determine the content type of this file if(args[0].endsWith(".html") || args[0].endsWith(".htm") ) { contentType = "text/html"; } else { contentType = "text/plain"; } // read the file into the string theData try { String thisLine; while((thisLine = dis.readLine()) != null) { theData += thisLine + "\n"; } } catch(Exception e) { System.err.println("Error " + e); } }


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catch(Exception e) { System.err.println(e); System.err.println("usage: java onefile filename port"); System.exit(1); } // set the port to listen on try { thePort = Integer.parseInt(args[1]); if(thePort < 0 || thePort > 65535) thePort = 80; } catch(Exception e) { thePort = 80; }


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// create a server socket try { ss = new ServerSocket(thePort); System.out.println("Accepting connections on port " + ss.getLocalPort()); System.out.println("Data to be sent:"); System.out.println(theData); while(true) { // stop and wait for a connection Socket socketTemp = ss.accept(); // we have a socket so create a handler OneFile fs = new OneFile(socketTemp); // start the handler running fs.start(); } } catch(IOException e) {System.out.println("Socket error"); } }}

carnegie mellon university, graduate school of industrial administration 1 event handling inner...

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