Concurrency: Java Threads

(lectures programs)

Sun OnLine Documentations

Thread Basics

Example: SimpleThread (Run  Applet)

public class SimpleThread extends Thread {

private int countDown = 50;

private static int threadCount = 0;

private int threadNumber = ++threadCount;

public SimpleThread () {

System.out.println("Making " + threadNumber);

}

public void run() {

while (true) {

System.out.println("Thread"+threadNumber+countDown);

if (--countDown == 0) return;

}

}

public static void main(String[] args) {

for(int i = 0; i < 5; i++)

new SimpleThread().start();

System.out.println("All Threads Started");

}

}

Example: Counter4 (Run Applet)

public class Counter4 extends JApplet {

private JButton startB = new JButton("Start");

private Ticker[] s;

class Ticker extends Thread {

private JToggleButton b = new JToggleButton("Toggle");

private JTextField t = new JTextField(10);

private int count = 0;

private boolean runFlag = true;

public Ticker() {

b.addActionListener(new ToggleL());

JPanel p = new JPanel();

p.add(t);

p.add(b);

getContentPane().add(p);

}

class ToggleL implements ActionListener {

public void actionPerformed(ActionEvent e) {

runFlag = !runFlag;

}

}

public void run() {

while (true) {

if (runFlag)t.setText(Integer.toString(count++));

try {

sleep(200);

} catch(InterruptedException e) {

System.err.println("Interrupted");

}

}

}

}

class StartL implements ActionListener {

public void actionPerformed(ActionEvent e) {

startB.setBackground(Color.red);

startB.setEnabled(false);

for (int i = 0; i < s.length; i++)

s[i].start();

}

}

}

public void init() {

Container cp = getContentPane();

cp.setLayout(new FlowLayout());

s = new Ticker[4];

for (int i = 0; i < s.length; i++)

s[i] = new Ticker();

startB.addActionListener(new StartL());

cp.add(startB);

}

public static void main (String[] args) {

Counter4 applet = new Counter4 ();

Console.run (applet, 200, 200);

}

}

You can run this as an application: 

% java Counter4

Wait, Notify & Interrupt

Example: Notify() a waiting thread (Run Applet)

public class Notify extends JApplet {
private JTextField txt = new JTextField(20);
private JButton
suspendB = new JButton("Suspend"),
resumeB = new JButton("Resume");
private Suspendable suspendableThread = new Suspendable();
class Suspendable extends Thread {
private int count = 0;
private boolean suspendedFlag = false;

public Suspendable() {
start();
}
public synchronized void funSuspend() {
suspendedFlag = true;
}
public synchronized void funResume() {
suspendedFlag = false;
notify();
}
public void run() {
while (true) {
txt.setText("Count: " + Integer.toString(count++));
synchronized (this) {
if(suspendedFlag) {
try{
txt.setText("Suspend Button is ON: wait()");
wait();
}
catch(InterruptedException e) {
System.err.println("wait Interrupted "+ e);
}
txt.setText("Resume Button is ON");
}
}// synch
try{
sleep(2000);
}
catch(InterruptedException e) {
System.err.println("sleep(): Interrupted " + e);
}
}//true
}//run
}//thread
public void init() {
Container cp = getContentPane();
cp.setLayout(new FlowLayout());
cp.add(txt);
suspendB.addActionListener( new ActionListener() {
public
void actionPerformed(ActionEvent e) {
suspendableThread.funSuspend();
suspendB.setEnabled(false);
suspendB.setBackground(Color.red);
resumeB.setEnabled(true);
resumeB.setBackground(Color.green);
}
}
);
cp.add(suspendB);
suspendB.setEnabled(true);
suspendB.setBackground(Color.green);
resumeB.addActionListener( new ActionListener() {
public
void actionPerformed(ActionEvent e) {
suspendableThread.funResume();
suspendB.setEnabled(true);
suspendB.setBackground(Color.green);
resumeB.setEnabled(false);
resumeB.setBackground(Color.red);
}
}
);
cp.add(resumeB);
resumeB.setEnabled(false);
resumeB.setBackground(Color.red);
}
public static void main(String[] args) {
Console.run(new Notify(), 300, 100);
}
}//JApplet

Example: Interrupt() a waiting thread (Run Applet)

public class Interrupt extends JApplet {
private JTextField txt = new JTextField(30);
private JButton
suspendB = new JButton("Suspend"),
interruptB = new JButton("Interrupt");
private Suspendable suspendableThread = new Suspendable();
class Suspendable extends Thread {
private int count = 0;
private boolean suspendedFlag = false;

public Suspendable() {
start();
}
public synchronized void funSuspend() {
suspendedFlag = true;
}
public synchronized void funInterrupt() {
suspendedFlag = false;
interrupt();
}
public void run() {
while (true) {
txt.setText("Count: " + Integer.toString(count++));
synchronized (this) {
if(suspendedFlag) {
try{
txt.setText("Suspend Button is ON: wait()");
wait();
}
catch(InterruptedException e) {
txt.setText("Interrupt Button is ON: "+ e);
System.err.println("wait Interrupted "+ e);
}
}
}// synch
try{
sleep(2000);
}
catch(InterruptedException e) {
System.err.println("sleep(): Interrupted"+e);
}
}//true
}//run
}//thread
public void init() {
Container cp = getContentPane();
cp.setLayout(new FlowLayout());
cp.add(txt);
suspendB.addActionListener( new ActionListener() {
public
void actionPerformed(ActionEvent e) {
suspendableThread.funSuspend();
suspendB.setEnabled(false);
suspendB.setBackground(Color.red);
interruptB.setEnabled(true);
interruptB.setBackground(Color.green);
}
}
);
cp.add(suspendB);
suspendB.setEnabled(true);
suspendB.setBackground(Color.green);
interruptB.addActionListener( new ActionListener() {
public
void actionPerformed(ActionEvent e) {
suspendableThread.funInterrupt();
suspendB.setEnabled(true);
suspendB.setBackground(Color.green);
interruptB.setEnabled(false);
interruptB.setBackground(Color.red);
}
}
);
cp.add(interruptB);
interruptB.setEnabled(false);
interruptB.setBackground(Color.red);
}
public static void main(String[] args) {
Console.run(new Interrupt(), 400, 200);
}
}//JApplet

Example: Interrupt() a sleeping thread (Run Applet)

public class InterruptSleep extends JApplet {
private JTextField txt = new JTextField(30);
private JButton
interruptB = new JButton("Interrupt Sleep");
private Counting countingThread = new Counting();
class Counting extends Thread {
private int count = 0;
public Counting() {
start();
}
public synchronized void funInterrupt() {
System.err.println("Interrupt Button");
interrupt();
}
public void run() {
while (true) {
txt.setText("Count:"+Integer.toString(count++));
try{sleep(8000); }
catch(InterruptedException e) {
System.err.println("sleep 8 seconds:Interrupted");
}
}//true
}//run
}//thread
public void init() {
Container cp = getContentPane();
cp.setLayout(new FlowLayout());
cp.add(txt);
interruptB.addActionListener( new ActionListener() {
public void actionPerformed(ActionEvent e) {
countingThread.funInterrupt();
}
});
cp.add(interruptB);
interruptB.setEnabled(true);
interruptB.setBackground(Color.green);
}
public static void main(String[] args) {
Console.run(new InterruptSleep(), 400, 200);
}
}//JApplet