Java中scroll pane的使用（一）-- 动态改变其client的大小

package com.han;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Shape;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;

/**
* This application aims to dynamically change the client's size in a scroll
* pane.
*
* @author HAN
*
*/
@SuppressWarnings("serial")
public class ScrollDemo2 extends JPanel {
/**
* We can also use Vector to store a variable array. But the overhead will
* be more than ArrayList. So the difference between them is thread-safe or
* not.
*/
private ArrayList<Shape> circles;

private final int CIRCLE_DIAMETER = 100;

private Dimension area;// indicate area taken up by graphics.

private Color[] colors = { Color.BLACK, Color.BLUE, Color.CYAN,
Color.DARK_GRAY, Color.GRAY, Color.GREEN, Color.LIGHT_GRAY,
Color.MAGENTA, Color.ORANGE, Color.PINK, Color.RED, Color.YELLOW };

ScrollDemo2() {
// The constructor serves also as a content pane. This is a common
// trick: invoke the constructor with parameter from a constructor
// without parameter.
super(new BorderLayout());

// Allocate memory for member variables if necessary.
circles = new ArrayList<Shape>();
area = new Dimension(0, 0);

// Create "labelPanel".
JPanel labelPanel = new JPanel(new GridLayout(0, 1));
labelPanel
.add(new JLabel("Click left mouse button to place a circle."));
labelPanel.add(new JLabel(
"Click right mouse button to clear drawing area."));

// Create "drawingPane".
final JPanel drawingPane = new JPanel() {
@Override
protected void paintComponent(Graphics g) {
// Paint first the default behavior of the JPanel painting,
// which includes fill the whole area with a background color we
// set. This arrives to the effect that "clear the panel", which
// can also be realized by setColor followed by fillRect.
super.paintComponent(g);
// g.setColor(getBackground());
// g.fillRect(0, 0, getWidth(), getHeight());

Graphics2D g2 = (Graphics2D) g;

// For showing always all drawn circles even if you resize the
// window, we are forced to draw all circles in the "current"
// painting.
for (int i = 0; i < circles.size(); i++) {
g2.setColor(colors[i % colors.length]);
g2.fill(circles.get(i));
}
}
};

drawingPane.setOpaque(true);

// Set the background property, which you can get by getBackground.
drawingPane.setBackground(Color.WHITE);

drawingPane.addMouseListener(new MouseAdapter() {
@Override
public void mouseReleased(MouseEvent e) {
boolean changed = false;
int x = e.getX() - CIRCLE_DIAMETER / 2;
int y = e.getY() - CIRCLE_DIAMETER / 2;
if (x < 0)
x = 0;
if (y < 0)
y = 0;

if (SwingUtilities.isLeftMouseButton(e)) {
circles.add(new Ellipse2D.Double(x, y, CIRCLE_DIAMETER,
CIRCLE_DIAMETER));

// Here we can use two repaint methods: the one with
// parameter and the other without.
// repaint(clip) will repaint updates only in the desired
// region (as clip), which can have a more efficient
// performance than use directly repaint().
drawingPane.repaint(x, y, CIRCLE_DIAMETER, CIRCLE_DIAMETER);
// drawingPane.repaint();

// Update the area taken up by graphics.
int thisWidth = x + CIRCLE_DIAMETER;
if (thisWidth > area.width) {
area.width = thisWidth;
changed = true;
}
int thisHeight = y + CIRCLE_DIAMETER;
if (thisHeight > area.height) {
area.height = thisHeight;
changed = true;
}
} else if (SwingUtilities.isRightMouseButton(e)) {
circles.clear();

// Because in this case we want to change the whole painting
// area, use the repaint() directly.
drawingPane.repaint();

area.width = 0;
area.height = 0;
changed = true;
}

if (changed) {
// The setPreferredSize method is to be used in a
// combination way with the revalidate() method.
drawingPane.setPreferredSize(area);

// Let the scroll pane know to update itself especially its
// scroll bars.
drawingPane.revalidate();
}
}
});

// Put the drawingPane to a scroll pane.
JScrollPane scrollPane = new JScrollPane(drawingPane);
// setPreferredSize for the first "pack()" use.
scrollPane.setPreferredSize(new Dimension(200, 200));

// Lay out the content pane.
add(labelPanel, BorderLayout.NORTH);
add(scrollPane, BorderLayout.CENTER);
}

/**
* For thread safety, this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
// Create and set up the window.
JFrame frame = new JFrame("ScrollDemo2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

// Create and set up the content pane.
JPanel contentPane = new ScrollDemo2();
contentPane.setOpaque(true);// Content pane must be opaque.
frame.setContentPane(contentPane);

// Display the window.
frame.pack();
frame.setVisible(true);
}

public static void main(String[] args) {
// Schedule a job for the event-dispatching thread:
// creating and showing this application's GUI.
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
createAndShowGUI();
}
});
}
}