用 java 怎么做进度条？

用 java 怎么做进度条？

import java.awt.Canvas;import java.awt.Color;import java.awt.Graphics;public class MyProgressBar extends Canvas { private float scaleSize; private float currentValue; public MyProgressBar() { this(100, 50); } public MyProgressBar(float scaleSize, float currentValue) { this.scaleSize = scaleSize; this.currentValue = currentValue; this.setBackground(Color.lightGray); this.setForeground(Color.magenta); setSize(150, 25); } public float getCurrentValue() { return currentValue; } public void setCurrentValue(float currentValue) { this.currentValue = Math.max(0, currentValue); if (this.scaleSize < this.currentValue) { this.currentValue = this.scaleSize; } } public float getScaleSize() { return scaleSize; } public void setScaleSize(float scaleSize) { this.scaleSize = Math.max(1.0f, scaleSize); if (this.scaleSize < this.currentValue) { this.scaleSize = this.currentValue; } } public synchronized void paint(Graphics g) { int w = getSize().width; int h = getSize().height; g.setColor(getBackground()); g.fillRect(1, 1, w - 2, h - 2); g.fill3DRect(0, 0, w - 1, h - 1, true); g.setColor(getForeground()); g.fillRect(3, 3, (int) (currentValue * (w - 6) / scaleSize), h - 6); }}下面是程序执行入口点：import java.awt.FlowLayout;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;public class TestMyProgressBar extends JFrame implements Runnable, ActionListener { private MyProgressBar bar; private JButton btnStart; static TestMyProgressBar tmpb; public TestMyProgressBar() { setSize(400, 300); setLocation(400, 400); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setTitle("演示自定义进度条"); setLayout(new FlowLayout()); btnStart = new JButton("开始"); this.add(btnStart); btnStart.addActionListener(this); bar = new MyProgressBar(); setVisible(true); } public static void main(String[] args) { tmpb = new TestMyProgressBar(); } @Override public void run() { for (int i = 1; i <= 20; i++) { int x = i * 5; bar.setCurrentValue(x); if (x > 0 && x < 100) { btnStart.setEnabled(false); } if (x == 100) { btnStart.setEnabled(true); } try { Thread.sleep(200); add(bar); } catch (InterruptedException e) { e.printStackTrace(); } } } @Override public void actionPerformed(ActionEvent e) { if (e.getActionCommand().equals("开始")) { Thread t = new Thread(tmpb); t.start(); } }}