scrollablepicture.java

这是一个英文版的《Java程序设计与问题解决》现在好多大学都当成教材

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

/* ScrollablePicture.java is used by ScrollDemo.java. */

public class ScrollablePicture extends JLabel
                               implements Scrollable {

    private int maxUnitIncrement = 1;
    private boolean missingPicture = false;

    public ScrollablePicture(ImageIcon i, int m) {
        super(i);
        if (i == null) {
            missingPicture = true;
            setText("No picture found.");
            setHorizontalAlignment(CENTER);
            setOpaque(true);
            setBackground(Color.white);
        }
        maxUnitIncrement = m;
    }

    public Dimension getPreferredSize() {
        if (missingPicture) {
            return new Dimension(320, 480);
        } else {
            return super.getPreferredSize();
        }
    }

    public Dimension getPreferredScrollableViewportSize() {
        return getPreferredSize();
    }

    public int getScrollableUnitIncrement(Rectangle visibleRect,
                                          int orientation,
                                          int direction) {
        //Get the current position.
        int currentPosition = 0;
        if (orientation == SwingConstants.HORIZONTAL) {
            currentPosition = visibleRect.x;
        } else {
            currentPosition = visibleRect.y;
        }

        //Return the number of pixels between currentPosition
        //and the nearest tick mark in the indicated direction.
        if (direction < 0) {
            int newPosition = currentPosition -
                             (currentPosition / maxUnitIncrement) *
                              maxUnitIncrement;
            return (newPosition == 0) ? maxUnitIncrement : newPosition;
        } else {
            return ((currentPosition / maxUnitIncrement) + 1) *
                   maxUnitIncrement - currentPosition;
        }
    }

    public int getScrollableBlockIncrement(Rectangle visibleRect,
                                           int orientation,
                                           int direction) {
        if (orientation == SwingConstants.HORIZONTAL) {
            return visibleRect.width - maxUnitIncrement;
        } else {
            return visibleRect.height - maxUnitIncrement;
        }
    }

    public boolean getScrollableTracksViewportWidth() {
        return false;
    }

    public boolean getScrollableTracksViewportHeight() {
        return false;
    }

    public void setMaxUnitIncrement(int pixels) {
        maxUnitIncrement = pixels;
    }
}