1.初识Java多线程

1.进程、线程、多线程的区别

进程：

线程：

多线程：

2.使用Java中的线程

• 1.继承java.lang.Thread类
• 2.实现java.lang.Runnable接口

2.1自定义继承Thread类

public class CustomerThread extends Thread {
    @Override
    public void run() {
        super.run();
        System.out.println("customer thread!");
    }
}

public class Client {
    public static void main(String[] args) {
        CustomerThread customerThread = new CustomerThread();
        customerThread.start();
        System.out.println("main 函数");
    }
}

2.2自定义继承Runnable接口

public class CustomerRunable implements Runnable {
    @Override
    public void run() {
        System.out.println("customer runable.");
    }
}

public class Client {
    public static void main(String[] args) {
        CustomerRunable customerRunable = new CustomerRunable();
        Thread thread = new Thread(customerRunable);
        thread.start();
        System.out.println("main 函数");
    }
}

3.实例变量与线程安全

3.1不共享线程实例变量

public class MyThread extends Thread {
    private int count = 5;


    public MyThread(String name) {
        super();
        this.setName(name);
    }

    @Override
    public void run() {
        super.run();
        while (count > 0) {
            count--;
            System.out.println("由" + this.currentThread().getName() + "计算，count=" + count);
        }
    }
}

public class Client {
    public static void main(String[] args) {
        MyThread a = new MyThread("a");
        MyThread b = new MyThread("b");
        MyThread c = new MyThread("c");
        a.start();
        b.start();
        c.start();
    }
}

3.2共享线程实例变量

public class MyThread extends Thread {
    private int count = 5;


    public MyThread(String name) {
        super();
        this.setName(name);
    }

    @Override
    public void run() {
        super.run();
        count--;
        System.out.println("由" + this.currentThread().getName() + "计算，count=" + count);
    }
}

public class Client {
    public static void main(String[] args) {
        MyThread myThread = new MyThread();
        Thread a = new Thread(myThread, "a");
        Thread b = new Thread(myThread, "b");
        Thread c = new Thread(myThread, "c");
        Thread d = new Thread(myThread, "d");
        a.start();
        b.start();
        c.start();
        d.start();
    }
}

3.3线程安全

4.currentThread

5.isAlive

6.sleep

7.getId

8.停止线程

8.1判断线程是否停止状态

• 1.静态方法interrupted()

/**
 * Tests whether the current thread has been interrupted.  The
 * <i>interrupted status</i> of the thread is cleared by this method.  In
 * other words, if this method were to be called twice in succession, the
 * second call would return false (unless the current thread were
 * interrupted again, after the first call had cleared its interrupted
 * status and before the second call had examined it).
 *
 * <p>A thread interruption ignored because a thread was not alive
 * at the time of the interrupt will be reflected by this method
 * returning false.
 *
 * @return  <code>true</code> if the current thread has been interrupted;
 *          <code>false</code> otherwise.
 * @see #isInterrupted()
 * @revised 6.0
 */
public static boolean interrupted() {
    return currentThread().isInterrupted(true);
}

• 2.实例方法isInterrupted()

public boolean isInterrupted() {
    return isInterrupted(false);
}

8.2代码演示

public class CustomerThread extends Thread {
    @Override
    public void run() {
        super.run();
        for (int i = 0; i < 100; i++) {
            if (this.isInterrupted()) {
                System.out.println("已接收到停止命令！");
                break;
            }
            System.out.println(String.format("i=%s", i));
        }
        System.out.println("哈哈，我还在...");
    }
}

public class Client {
    public static void main(String[] args) throws InterruptedException {
        CustomerThread thread = new CustomerThread();
        thread.start();
        Thread.sleep(20);
        thread.interrupt();
        System.out.println(thread.isInterrupted());
        System.out.println("main函数执行完毕！");

    }
}

...
i=48
已接收到停止命令！
哈哈，我还在...
true
main函数执行完毕！

• try-catch方式

public class CustomerThread extends Thread {
    @Override
    public void run() {
        super.run();
        try{
            for (int i = 0; i < 100; i++) {
                if (this.isInterrupted()) {
                    System.out.println("已接收到停止命令！");
                    throw new InterruptedException();
                }
                System.out.println(String.format("i=%s", i));
            }
            System.out.println("哈哈，我还在...");
        }
        catch (InterruptedException error){
            System.out.println(error.getMessage());
            error.printStackTrace();
        }
    }
}

• return方式

@Override
public void run() {
    super.run();
    for (int i = 0; i < 100; i++) {
        if (this.isInterrupted()) {
            System.out.println("已接收到停止命令！");
            return;
        }
        System.out.println(String.format("i=%s", i));
    }
    System.out.println("哈哈，我还在...");
}

9.yield

Thread.yield();

10.线程的优先级

public final void setPriority(int newPriority) {
    ThreadGroup g;
    checkAccess();
    if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
        throw new IllegalArgumentException();
    }
    if((g = getThreadGroup()) != null) {
        if (newPriority > g.getMaxPriority()) {
            newPriority = g.getMaxPriority();
        }
        setPriority0(priority = newPriority);
    }
}

11.守护线程