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

动态改变scroll pane的client的大小，并达到其滚动条出现当client超出我们设定的view port大小时。

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() {@Overrideprotected 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() {@Overridepublic 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() {@Overridepublic void run() {createAndShowGUI();}});}}