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多线程编程

线程基础

创建线程

方式一：继承Thread类

public class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("线程运行中：" + Thread.currentThread().getName());
    }
}

// 使用
MyThread thread = new MyThread();
thread.start();

方式二：实现Runnable接口

public class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("线程运行中：" + Thread.currentThread().getName());
    }
}

// 使用
Thread thread = new Thread(new MyRunnable());
thread.start();

// 使用Lambda表达式
Thread thread2 = new Thread(() -> {
    System.out.println("Lambda线程运行中");
});
thread2.start();

方式三：实现Callable接口

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

public class MyCallable implements Callable<Integer> {
    @Override
    public Integer call() throws Exception {
        int sum = 0;
        for (int i = 1; i <= 100; i++) {
            sum += i;
        }
        return sum;
    }
}

// 使用
FutureTask<Integer> futureTask = new FutureTask<>(new MyCallable());
Thread thread = new Thread(futureTask);
thread.start();

// 获取返回值
Integer result = futureTask.get();
System.out.println("1到100的和：" + result);  // 5050

线程同步

synchronized关键字

public class Counter {
    private int count = 0;
    
    // 同步方法
    public synchronized void increment() {
        count++;
    }
    
    // 同步代码块
    public void decrement() {
        synchronized (this) {
            count--;
        }
    }
    
    public int getCount() {
        return count;
    }
}

Lock接口

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class SafeCounter {
    private int count = 0;
    private final Lock lock = new ReentrantLock();
    
    public void increment() {
        lock.lock();
        try {
            count++;
        } finally {
            lock.unlock();
        }
    }
    
    public int getCount() {
        return count;
    }
}

线程通信

wait/notify

public class ProducerConsumer {
    private final Object lock = new Object();
    private boolean hasData = false;
    
    public void produce() throws InterruptedException {
        synchronized (lock) {
            while (hasData) {
                lock.wait();  // 等待消费
            }
            // 生产数据
            hasData = true;
            System.out.println("生产数据");
            lock.notify();  // 通知消费者
        }
    }
    
    public void consume() throws InterruptedException {
        synchronized (lock) {
            while (!hasData) {
                lock.wait();  // 等待生产
            }
            // 消费数据
            hasData = false;
            System.out.println("消费数据");
            lock.notify();  // 通知生产者
        }
    }
}

线程池

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

// 创建固定大小线程池
ExecutorService executor = Executors.newFixedThreadPool(5);

// 提交任务
for (int i = 0; i < 10; i++) {
    final int taskId = i;
    executor.submit(() -> {
        System.out.println("任务 " + taskId + " 由 " + 
            Thread.currentThread().getName() + " 执行");
    });
}

// 关闭线程池
executor.shutdown();

ThreadPoolExecutor

import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;

ThreadPoolExecutor executor = new ThreadPoolExecutor(
    2,                      // 核心线程数
    5,                      // 最大线程数
    60L,                    // 空闲线程存活时间
    TimeUnit.SECONDS,       // 时间单位
    new ArrayBlockingQueue<>(10)  // 任务队列
);

executor.execute(() -> {
    System.out.println("执行任务");
});

executor.shutdown();