Question

关于Java中进度条的问题

为什么我在读取一个文件时进度条一直不走，一直0%，而到了文件读取完成时就一下子跳到100%了，中间的过程进度条工程进度条一直在0%处不动?

//item为读取菜单 pro为进度条

item.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
File file = new File("F:/111.wmv");
long size = file.length();
byte[] bts = new byte[1024*1024];
int length = 0;
long cLength = 0;
try {
InputStream stream = new FileInputStream(file);
OutputStream os = new FileOutputStream(new File("F:/q.wmv"));
while((length=stream.read(bts))>0){
cLength += length;
os.write(bts,0,length);
int value = (int)(cLength*100/size);
pro.setValue(value);
}
os.close();
stream.close();
} catch (FileNotFoundException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
}
});

Answer 1

import java.awt.BorderLayout;
import java.awt.Cursor;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;

public class Bar extends JFrame implements PropertyChangeListener
{
	private static final long serialVersionUID = 1L;

	private JProgressBar progressBar;

	private JButton copy;

	private Task task;

	public Bar(String title)
	{
		setTitle(title);
		setLayout(new BorderLayout());
		progressBar = new JProgressBar(0, 100);
		progressBar.setValue(0);
		progressBar.setStringPainted(true);

		add(progressBar, BorderLayout.CENTER);
		copy = new JButton("拷贝");
		copy.addActionListener(new ActionListener()
		{
			@Override
			public void actionPerformed(ActionEvent e)
			{
				start();
				copy.setEnabled(false);
			}
		});
		add(copy, BorderLayout.EAST);
	}

	class Task extends SwingWorker<Void, Void>
	{
		@Override
		public Void doInBackground()
		{
			setProgress(0);
			File file = new File("aa.mp3");
			long size = file.length();
			byte[] bts = new byte[1024 * 10];
			int length = 0;
			long cLength = 0;
			try
			{
				InputStream stream = new FileInputStream(file);
				OutputStream os = new FileOutputStream(new File("a.mp3"));
				while((length = stream.read(bts)) > 0)
				{
					os.write(bts, 0, length);
					cLength += length;
					setProgress((int) (cLength * 100 / size));
					Thread.sleep(100);
				}
				os.close();
				stream.close();
			}
			catch(Exception e1)
			{
				e1.printStackTrace();
			}
			return null;
		}

		@Override
		public void done()
		{
			setTitle("拷贝完毕");
			Toolkit.getDefaultToolkit().beep();
			copy.setEnabled(true);
			setCursor(null);
		}
	}

	public void propertyChange(PropertyChangeEvent evt)
	{
		if("progress" == evt.getPropertyName())
		{
			int progress = (Integer) evt.getNewValue();
			progressBar.setValue(progress);
		}
	}

	private void start()
	{
		task = new Task();
		task.addPropertyChangeListener(this);
		task.execute();
		setTitle("正在拷贝...");
		setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
	}

	private static void createAndShowGUI()
	{
		Bar frame = new Bar("Bar");
		frame.setAlwaysOnTop(true);
		frame.setSize(280, 60);
		frame.setResizable(false);
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}

	public static void main(String[] args)
	{
		javax.swing.SwingUtilities.invokeLater(new Runnable()
		{
			public void run()
			{
				createAndShowGUI();
			}
		});
	}
}

Answer 2

你需要另外再开一个线程

追问

代码该怎么改呢？我还没学到多线程