A simple syntax question, pls help

[Jon Lee]

The following code is taken from "Core Java 7ED". There is one line of code I can not understand. That line No. is 90. What does it mean??? I never read a "for" loop code like this. Pls give some hints, Thnx a lot!

  1. import java.awt.*;
  2. import java.awt.event.*;
  3. import java.awt.geom.*;
  4. import java.util.*;
  5. import javax.swing.*;
  6.
  7. /**
  8.    Shows an animated bouncing ball.
  9. */
 10. public class Bounce
 11. {
 12.    public static void main(String[] args)
 13.    {
 14.       JFrame frame = new BounceFrame();
 15.       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 16.       frame.setVisible(true);
 17.    }
 18. }
 19.
 20. /**
 21.    A ball that moves and bounces off the edges of a
 22.    rectangle
 23. */
 24. class Ball
 25. {
 26.    /**
 27.       Moves the ball to the next position, reversing direction
 28.       if it hits one of the edges
 29.    */
 30.    public void move(Rectangle2D bounds)
 31.    {
 32.       x += dx;
 33.       y += dy;
 34.       if (x < bounds.getMinX())
 35.       {
 36.          x = bounds.getMinX();
 37.          dx = -dx;
 38.       }
 39.       if (x + XSIZE >= bounds.getMaxX())
 40.       {
 41.          x = bounds.getMaxX() - XSIZE;
 42.          dx = -dx;
 43.       }
 44.       if (y < bounds.getMinY())
 45.       {
 46.          y = bounds.getMinY();
 47.          dy = -dy;
 48.       }
 49.       if (y + YSIZE >= bounds.getMaxY())
 50.       {
 51.          y = bounds.getMaxY() - YSIZE;
 52.          dy = -dy;
 53.       }
 54.    }
 55.
 56.    /**
 57.       Gets the shape of the ball at its current position.
 58.    */
 59.    public Ellipse2D getShape()
 60.    {
 61.       return new Ellipse2D.Double(x, y, XSIZE, YSIZE);
 62.    }
 63.
 64.    private static final int XSIZE = 15;
 65.    private static final int YSIZE = 15;
 66.    private double x = 0;
 67.    private double y = 0;
 68.    private double dx = 1;
 69.    private double dy = 1;
 70. }
 71.
 72. /**
 73.    The panel that draws the balls.
 74. */
 75. class BallPanel extends JPanel
 76. {
 77.    /**
 78.       Add a ball to the panel.
 79.       @param b the ball to add
 80.    */
 81.    public void add(Ball b)
 82.    {
 83.       balls.add(b);
 84.    }
 85.
 86.    public void paintComponent(Graphics g)
 87.    {
 88.       super.paintComponent(g);
 89.       Graphics2D g2 = (Graphics2D) g;
 90.       [B]for (Ball b : balls)[/B]
 91.       {
 92.          g2.fill(b.getShape());
 93.       }
 94.    }
 95.
 96.    private ArrayList<Ball> balls = new ArrayList<Ball>();
 97. }
 98.
 99. /**
100.    The frame with panel and buttons.
101. */
102. class BounceFrame extends JFrame
103. {
104.    /**
105.       Constructs the frame with the panel for showing the
106.       bouncing ball and Start and Close buttons
107.    */
108.    public BounceFrame()
109.    {
110.       setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
111.       setTitle("Bounce");
112.
113.       panel = new BallPanel();
114.       add(panel, BorderLayout.CENTER);
115.       JPanel buttonPanel = new JPanel();
116.       addButton(buttonPanel, "Start",
117.          new ActionListener()
118.          {
119.             public void actionPerformed(ActionEvent event)
120.             {
121.                addBall();
122.             }
123.          });
124.
125.       addButton(buttonPanel, "Close",
126.          new ActionListener()
127.          {
128.             public void actionPerformed(ActionEvent event)
129.             {
130.                System.exit(0);
131.             }
132.          });
133.       add(buttonPanel, BorderLayout.SOUTH);
134.    }
135.
136.    /**
137.       Adds a button to a container.
138.       @param c the container
139.       @param title the button title
140.       @param listener the action listener for the button
141.    */
142.    public void addButton(Container c, String title, ActionListener listener)
143.    {
144.       JButton button = new JButton(title);
145.       c.add(button);
146.       button.addActionListener(listener);
147.    }
148.
149.    /**
150.       Adds a bouncing ball to the panel and makes
151.       it bounce 1,000 times.
152.    */
153.    public void addBall()
154.    {
155.       try
156.       {
157.          Ball ball = new Ball();
158.          panel.add(ball);
159.
160.          for (int i = 1; i <= STEPS; i++)
161.          {
162.             ball.move(panel.getBounds());
163.             panel.paint(panel.getGraphics());
164.             Thread.sleep(DELAY);
165.          }
166.       }
167.       catch (InterruptedException e)
168.       {
169.       }
170.    }
171.
172.    private BallPanel panel;
173.    public static final int DEFAULT_WIDTH = 450;
174.    public static final int DEFAULT_HEIGHT = 350;
175.    public static final int STEPS = 1000;
176.    public static final int DELAY = 3;
177. }

[ August 13, 2005: Message edited by: Jon Lee ]
[ August 13, 2005: Message edited by: Jon Lee ]

[Barry Gaunt]

It's the new for loop construct that appeared in Java 5.0. You can read it as "for each Ball b in the collection (or array) balls, perform the following (whatever is in the {})". It is known as the "foreach" construct.
You can use break or continue as you would in a normal loop.
[ August 13, 2005: Message edited by: Barry Gaunt ]

[Megs Maquito]

this is the enhanced for loop as said. It means go through every element of balls ArrayList as you go through the list one at a time starting from [0]and put the value in b each time you do so.

[Layne Lund]

Are you reading Volume 1-Fundamentals or Volume 2-Advanced Topics? Volume 1 will explain this and other new features that come with Java 5.0, so it might be worth your time buying the new edition of Volume 1 even if you already own an older edition.

Layne

[Jon Lee]

Oh, I see. I dont read volume one yet. Maybe I should go through volume one qucikly to see the new features in Java 5.0.

Thnx for your replies, guys.

[Please do not offer to share copyrighted materials through JavaRanch. In fact, don't offer to share them at all. The people who produce such things deserve to be paid properly for their work -- mfe]

Cheers
[ August 16, 2005: Message edited by: Michael Ernest ]

[Layne Lund]

That's a very generous offer, but if the authors or publishers see it, you may be heading for some trouble since they own the copyrights and probably frown on people giving it away without their permission. In fact, the authors were here at the Ranch fairly recently for a book promotion...

Layne

[Barry Gaunt]

Originally posted by Layne Lund:
That's a very generous offer, but if the authors or publishers see it, you may be heading for some trouble since they own the copyrights and probably frown on people giving it away without their permission. In fact, the authors were here at the Ranch fairly recently for a book promotion...

Layne

Thank you for mentioning that Layne. Jon please take notice.

[Jon Lee]

Guys, thnx for your reminder. I will not share the books any more. BTW, the CORE Java series are great books for beginners. It is worth your money.