java 运用多线程

Java中的多线程可以通过继承Thread类或实现Runnable接口来实现。以下是两个Java多线程的例子：

1. 多线程下载文件并显示进度条

import java.io.*;
import java.net.*;

public class DownloadFile extends Thread {
    private String url;
    private String fileName;
    private int threadNum;
    private int startPos;
    private int endPos;
    private int curPos;
    private int fileSize;
    private int downloadedSize;

    public DownloadFile(String url, String fileName, int threadNum) {
        this.url = url;
        this.fileName = fileName;
        this.threadNum = threadNum;
    }

    public void run() {
        try {
            URL fileUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);            int responseCode = conn.getResponseCode();
            if (responseCode == 206) {
                fileSize = conn.getContentLength();
                InputStream is = conn.getInputStream();
                RandomAccessFile raf = new RandomAccessFile(fileName, "rw");
                raf.seek(startPos);
                byte[] buffer = new byte[1024];
                int len;
                while ((len = is.read(buffer)) != -1) {
                    raf.write(buffer, 0, len);
                    curPos += len;
                    downloadedSize += len;
                }
                is.close();
                raf.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        String url = "http://example.com/file.zip";
        String fileName = "file.zip";
        int threadNum = 5;
        try {
            URL fileUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            int responseCode = conn.getResponseCode();
            if (responseCode == 200) {
                int fileSize = conn.getContentLength();
                int blockSize = fileSize / threadNum;
                for (int i = 0; i < threadNum; i++) {
                    int startPos = i * blockSize;
                    int endPos = (i + 1) * blockSize - 1;
                    if (i == threadNum - 1) {
                        endPos = fileSize - 1;
                    }
                    DownloadFile downloadFile = new DownloadFile(url, fileName, threadNum);
                    downloadFile.startPos = startPos;
                    downloadFile.endPos = endPos;
                    downloadFile.start();
                }
                int curPos = 0;
                while (curPos < fileSize) {
                    System.out.print("[");
                    int percent = curPos * 100 / fileSize;
                    for (int i = 0; i < percent / 2; i++) {
                        System.out.print("=");
                    }
                    for (int i = percent / 2; i < 50; i++) {
                        System.out.print(" ");
                    }
                    System.out.print("] " + percent + "%\r");
                    Thread.sleep(1000);
                    curPos = 0;
                    for (int i = 0; i < threadNum; i++) {
                        curPos += downloadFile.curPos;
                    }
                }
                System.out.println();
                System.out.println("Download completed!");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2. 多线程控制小球运动

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

public class BallGame extends JFrame implements Runnable {
    private int x = 50;
    private int y = 50;
    private int size = 50;
    private Color color = Color.RED;
    private int speed = 10;
    private boolean isRunning = true;

    public BallGame() {
        setTitle("Ball Game");
        setSize(500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());
        JPanel panel = new JPanel();
        panel.setLayout(new FlowLayout());
        JLabel sizeLabel = new JLabel("Size:");
        JSlider sizeSlider = new JSlider(JSlider.HORIZONTAL, 10, 100, 50);
        sizeSlider.setMajorTickSpacing(10);
        sizeSlider.setMinorTickSpacing(5);
        sizeSlider.setPaintTicks(true);
        sizeSlider.setPaintLabels(true);
        sizeSlider.addChangeListener(new ChangeListener() {
            public void stateChanged(ChangeEvent e) {
                size = sizeSlider.getValue();
            }
        });
        JLabel colorLabel = new JLabel("Color:");
        JComboBox<String> colorComboBox = new JComboBox<String>();
        colorComboBox.addItem("Red");
        colorComboBox.addItem("Green");
        colorComboBox.addItem("Blue");
        colorComboBox.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String colorString = (String) colorComboBox.getSelectedItem();
                if (colorString.equals("Red")) {
                    color = Color.RED;
                } else if (colorString.equals("Green")) {
                    color = Color.GREEN;
                } else if (colorString.equals("Blue")) {
                    color = Color.BLUE;
                }
            }
        });
        panel.add(sizeLabel);
        panel.add(sizeSlider);
        panel.add(colorLabel);
        panel.add(colorComboBox);
        add(panel, BorderLayout.NORTH);
        add(new DrawPanel(), BorderLayout.CENTER);
        setVisible(true);
    }

    public void run() {
        while (isRunning) {
            if (x < 0 || x > getWidth() - size) {
                speed = -speed;
            }
            x += speed;
            repaint();
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private class DrawPanel extends JPanel {
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(color);
            g.fillOval(x, y, size, size);
        }
    }

    public static void main(String[] args) {
        BallGame ballGame = new BallGame();
        Thread thread = new Thread(ballGame);
        thread.start();
    }
}