Download Threads (1)

Threads (1)
Threads are “mini-programs” that only exist inside the context of a bigger
program. Taking a program running as a representation of a process, a thread
would be a sub-process, which shares the same resources allocated to that
process, and cannot live on its own.
However threads have their own execution stack and program counter, to name
a few…
P
T1
T2
T3
T4
When running threads, you get the impression that they are all being executed
“concurrently”, although in reality they normally comply to a round-robin
mechanism, where a time slice is allocated.
COMPSCI230S1C – Models Client programming
© Emilia Mendes
1
TwoThreadsTest.java
Creates two Thread objects: One displays “GREEN”, the other displays “RED”
Thread “green”
0 GREEN
1 GREEN
2 GREEN
3 GREEN
4 GREEN
5 GREEN
6 GREEN
7 GREEN
8 GREEN
9 GREEN
DONE! GREEN
Thread “red”
0 RED
1 RED
2 RED
3 RED
4 RED
5 RED
6 RED
7 RED
8 RED
9 RED
DONE! RED
Ideal Scenario:
COMPSCI230S1C – Models Client programming
© Emilia Mendes
2
TwoThreadsTest.java
But what really happens given sleep((int)(Math.random() * 1000)); is!
COMPSCI230S1C – Models Client programming
© Emilia Mendes
3
class TwoThreadsTest {
public static void main (String args[]) {
new SimpleThread("GREEN").start();
new SimpleThread("RED").start();
}
}
class SimpleThread extends Thread {
public SimpleThread(String str) {
super(str);
}
public void run() {
for (int i = 0; i < 10; i++) {
System.out.println(i + " " + getName());
try {
sleep((int)(Math.random() * 1000));
}
catch (InterruptedException e) {
}
}
System.out.println("DONE! " + getName());
}
}
Try four threads!!!
COMPSCI230S1C – Models Client programming
© Emilia Mendes
4
COMPSCI230S1C – Models Client programming
© Emilia Mendes
5
Threads and Interface Design
ƒ Here is an example of a red ball that bounces 1,000 times.
ƒ The first time you press “Start”, the ball starts to bounce.
ƒ If you immediately after that press the button “Close” it continues
bouncing as if you haven’t done anything….
ƒ You can only interact with the program when the ball has finished
bouncing!!!
ƒ Would you like to use an interface like that??????
COMPSCI230S1C – Models Client programming
© Emilia Mendes
6
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;
// Shows an animated bouncing ball.
public class BounceNoThreads {
public static void main(String[] args) {
JFrame frame = new BounceFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
class BounceFrame extends JFrame {
private BallCanvas canvas;
public static final int WIDTH = 250;
public static final int HEIGHT = 200;
public BounceFrame() {
setSize(WIDTH, HEIGHT);
setTitle("Bounce With No Threads");
Container contentPane = getContentPane();
canvas = new BallCanvas();
contentPane.add(canvas, BorderLayout.CENTER);
JPanel buttonPanel = new JPanel();
Method called
when you press
the button “Start”
addButton(buttonPanel, "Start",
new ActionListener()
{
public void actionPerformed(ActionEvent evt)
{
addBall(Color.red);
}
});
COMPSCI230S1C – Models Client programming
© Emilia Mendes
7
addButton(buttonPanel, "Close",
new ActionListener() {
public void actionPerformed(ActionEvent evt) {
System.exit(0);
}
});
contentPane.add(buttonPanel, BorderLayout.NORTH);
}
// Adds a button to a container c is the container object, title is the
// button title, listener is the action listener for the button
public void addButton(Container c, String title, ActionListener listener){
JButton button = new JButton(title);
c.add(button);
button.addActionListener(listener);
}
// Adds a bouncing ball to the canvas and makes it bounce 1,000 times.
public void addBall(Color color) {
try {
Ball b = new Ball(canvas, color);
canvas.add(b);
for (int i = 1; i <= 1000; i++) {
b.move();
Thread.sleep(5); //doesn’t create a new thread!!!!
}
}
catch (InterruptedException exception) {
}
}
}
Repeats this loop 1000
times, without giving a
chance to be interrupted
COMPSCI230S1C – Models Client programming
© Emilia Mendes
8
// The canvas that draws the balls.
class BallCanvas extends JPanel {
// Adds a ball to the canvas. Param b the ball to add
public void add(Ball b) {
balls.add(b);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
for (int i = 0; i < balls.size(); i++)
{
Ball b = (Ball)balls.get(i);
b.draw(g2);
}
}
private ArrayList balls = new ArrayList();
}
………..
COMPSCI230S1C – Models Client programming
© Emilia Mendes
9
Threaded Bouncing Ball
ƒ What is the difference here?
ƒ Each ball is created and associated with a thread that moves it 1,000
times, each time sleeping for 5 milliseconds.
ƒ This way, when one thread sleeps, it gives an opportunity to other
threads to execute, thus sharing resources…..
COMPSCI230S1C – Models Client programming
© Emilia Mendes 10
Threaded Bouncing Ball
Differences from previous code
Creates a new object ball,
Adds it to the Jpanel,
Creates a new thread and
associates it with the ball
object
Starts the thread
public void addBall(Color color) {
Ball b = new Ball(canvas, color);
canvas.add(b);
BallThread thread = new BallThread(b);
thread.start();
}
class BallThread extends Thread {
private Ball b;
// creates a new thread that will bounce the ball aBall
public BallThread(Ball aBall) {
b = aBall;
}
A Thousand times, the thread object
public void run() {
moves the ball once and then goes to
try {
sleep for five milliseconds.
for (int i = 1; i <= 1000; i++) {
By doing so, it gives an opportunity
b.move();
for another thread to take control.
sleep(5);
}
}
catch (InterruptedException exception) {
}
}
COMPSCI230S1C – Models Client programming
© Emilia Mendes 11
Threaded Bouncing Ball – source code
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;
public class BounceThreads {
public static void main(String[] args) {
JFrame frame = new BounceFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
class BounceFrame extends JFrame {
private BallCanvas canvas;
public static final int WIDTH = 250;
public static final int HEIGHT = 200;
public BounceFrame() {
setSize(WIDTH, HEIGHT);
setTitle("Bounce With Threads");
Container contentPane = getContentPane();
canvas = new BallCanvas();
contentPane.add(canvas, BorderLayout.CENTER);
JPanel buttonPanel = new JPanel();
COMPSCI230S1C – Models Client programming
© Emilia Mendes 12
addButton(buttonPanel, "Start", new ActionListener() {
public void actionPerformed(ActionEvent evt) {
addBall(Color.red);
}
});
addButton(buttonPanel, "Close", new ActionListener() {
public void actionPerformed(ActionEvent evt) {
System.exit(0);
}
});
contentPane.add(buttonPanel, BorderLayout.NORTH);
}
// Adds a button to a container.
// param c is the container object
// param title is the button title
// param listener is the action listener for the button
public void addButton(Container c, String title, ActionListener listener) {
JButton button = new JButton(title);
c.add(button);
button.addActionListener(listener);
}
// Adds a bouncing ball to the canvas and starts a thread.
public void addBall(Color color) {
Ball b = new Ball(canvas, color);
canvas.add(b);
BallThread thread = new BallThread(b);
thread.start();
}
}
COMPSCI230S1C – Models Client programming
© Emilia Mendes 13
class BallThread extends Thread {
private Ball b;
// creates a new thread that will bounce the ball aBall
public BallThread(Ball aBall) {
b = aBall;
}
public void run() {
try {
for (int i = 1; i <= 1000; i++) {
b.move();
sleep(5);
}
}
catch (InterruptedException exception) {
}
}
}
// The canvas that draws the balls.
class BallCanvas extends JPanel {
// Add a ball to the canvas. Param b the ball to add
public void add(Ball b) {
balls.add(b);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
for (int i = 0; i < balls.size(); i++) {
Ball b = (Ball)balls.get(i);
b.draw(g2);
COMPSCI230S1C – Models Client programming
© Emilia Mendes 14
}
}
private ArrayList balls = new ArrayList();
}
// A ball that moves and bounces off the edges of a component
class Ball {
private Component canvas;
private Color color;
private static final int XSIZE = 15;
private static final int YSIZE = 15;
private int x = 0;
private int y = 0;
private int dx = 2;
private int dy = 2;
// Constructs a ball in the upper left corner
// c the component in which the ball bounces
public Ball(Component c, Color col) {
canvas = c;
color = col;
}
// Draws the ball at its current position. Param g2 the graphics context
public void draw(Graphics2D g2) {
g2.setColor(color);
g2.fill(new Ellipse2D.Double(x, y, XSIZE, YSIZE));
}
// Moves the ball to the next position, reversing direction
// if it hits one of the edges
public void move() {
COMPSCI230S1C – Models Client programming
© Emilia Mendes 15
x += dx;
y += dy;
if (x < 0) {
x = 0;
dx = -dx;
}
if (x + XSIZE >= canvas.getWidth()) {
x = canvas.getWidth() - XSIZE;
dx = -dx;
}
if (y < 0) {
y = 0;
dy = -dy;
}
if (y + YSIZE >= canvas.getHeight()) {
y = canvas.getHeight() - YSIZE;
dy = -dy;
}
canvas.paint(canvas.getGraphics());
}
}
COMPSCI230S1C – Models Client programming
© Emilia Mendes 16
Exercise: Change the code for BounceThreads.java by adding another
button which starts BLUE balls, each associated with a thread.
What are the two small modifications you have to make?
COMPSCI230S1C – Models Client programming
© Emilia Mendes 17
ANSWER:
addButton(buttonPanel, "Start Red Ball", new ActionListener() {
public void actionPerformed(ActionEvent evt) {
addBall(Color.red);
}
});
addButton(buttonPanel, "Start Blue Ball", new ActionListener() {
public void actionPerformed(ActionEvent evt) {
addBall(Color.blue);
}
});
And what does need to change to add a green ball?
COMPSCI230S1C – Models Client programming
© Emilia Mendes 18