14.1 什么是线程

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;

/**
 * Created by Brave on 2016/12/10.
 */
public class MyBounce {
    public static void main(String[] args)
    {
        EventQueue.invokeLater(() -> {
            JFrame frame = new BounceFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
        });
    }
}

/**
 * The frame with ball component and buttons.
 */
class BounceFrame extends JFrame
{
    private BallComponent comp;
    public static final int STEPS = 1000;
    public static final int DELAY = 3;

    /**
     * Constructs the frame with the component for showing the bouncing ball and
     * Start and Close buttons
     */
    public BounceFrame()
    {
        setTitle("Bounce");
        comp = new BallComponent();
        add(comp, BorderLayout.CENTER);
        JPanel buttonPanel = new JPanel();
        addButton(buttonPanel, "Start", event -> addBall());
        addButton(buttonPanel, "Close", event -> System.exit(0));
        add(buttonPanel, BorderLayout.SOUTH);
        pack();
    }

    /**
     * Adds a button to a container.
     * @param c the container
     * @param title the button title
     * @param listener 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 panel and makes it bounce 1,000 times.
     */
    public void addBall()
    {
        try
        {
            Ball ball = new Ball();
            comp.add(ball);

            for (int i = 1; i <= STEPS; i++)
            {
                ball.move(comp.getBounds());
                comp.paint(comp.getGraphics());
                Thread.sleep(DELAY);
            }
        }
        catch (InterruptedException e)
        {
        }
    }
}
class BallComponent extends JPanel
{
    private static final int DEFAULT_WIDTH = 450;
    private static final int DEFAULT_HEIGHT = 350;

    private java.util.List balls = new ArrayList<>();

    /**
     * Add a ball to the component.
     * @param b the ball to add
     */
    public void add(Ball b)
    {
        balls.add(b);
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g); // erase background
        Graphics2D g2 = (Graphics2D) g;
        for (Ball b : balls)
        {
            g2.fill(b.getShape());
        }
    }

    public Dimension getPreferredSize() { return new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT); }
}

class Ball
{
    private static final int XSIZE = 15;
    private static final int YSIZE = 15;
    private double x = 0;
    private double y = 0;
    private double dx = 1;
    private double dy = 1;

    /**
     * Moves the ball to the next position, reversing direction if it hits one of the edges
     */
    public void move(Rectangle2D bounds)
    {
        x += dx;
        y += dy;
        if (x < bounds.getMinX())
        {
            x = bounds.getMinX();
            dx = -dx;
        }
        if (x + XSIZE >= bounds.getMaxX())
        {
            x = bounds.getMaxX() - XSIZE;
            dx = -dx;
        }
        if (y < bounds.getMinY())
        {
            y = bounds.getMinY();
            dy = -dy;
        }
        if (y + YSIZE >= bounds.getMaxY())
        {
            y = bounds.getMaxY() - YSIZE;
            dy = -dy;
        }
    }

    /**
     * Gets the shape of the ball at its current position.
     */
    public Ellipse2D getShape()
    {
        return new Ellipse2D.Double(x, y, XSIZE, YSIZE);
    }
}

---

1 使用线程给其他任务执行的机会

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

/**
 * Created by Brave on 2016/12/10.
 */
public class MyBounceThread {
    public static void main(String[] args)
    {
        EventQueue.invokeLater(() -> {
            JFrame frame = new BounceThreadFrame();
            frame.setTitle("BounceThread");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
        });
    }
}

/**
 * The frame with panel and buttons.
 */
class BounceThreadFrame extends JFrame
{
    private BallComponent comp;
    public static final int STEPS = 1000;
    public static final int DELAY = 5;


    /**
     * Constructs the frame with the component for showing the bouncing ball and
     * Start and Close buttons
     */
    public BounceThreadFrame()
    {
        comp = new BallComponent();
        add(comp, BorderLayout.CENTER);
        JPanel buttonPanel = new JPanel();
        addButton(buttonPanel, "Start", event -> addBall());
        addButton(buttonPanel, "Close", event -> System.exit(0));
        add(buttonPanel, BorderLayout.SOUTH);
        pack();
    }

    /**
     * Adds a button to a container.
     * @param c the container
     * @param title the button title
     * @param listener 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 to make it bounce
     */
    public void addBall()
    {
        Ball ball = new Ball();
        comp.add(ball);
        Runnable r = () -> {
            try
            {
                for (int i = 1; i <= STEPS; i++)
                {
                    ball.move(comp.getBounds());
                    comp.repaint();
                    Thread.sleep(DELAY);
                }
            }
            catch (InterruptedException e)
            {
            }
        };
        Thread t = new Thread(r);
        t.start();
    }
}