文章目錄
  1. 1. 实现Runnable接口
  2. 2. 继承Thread类

在Java中创建线程有两中方法,一种是实现Runnable接口,一种是继承Thread类

实现Runnable接口

  1. 将任务代码迁移到实现Runnable接口的类的run方法中

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    class MyRunnable implements Runnable {
    public void run() {
    task code
    }
    }
  2. 创建一个类对象:
    Runnable r = new MyRunnable()

  3. 由Runnable创建一个Thread对象
    Thread t = new Thread(r)
  4. 启动线程
    t.start()
    完整例子如下:
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    public class MyRunnable implements Runnable {
    @Override
    public void run() {
    System.out.println("Child: " + Thread.currentThread().getId());

    }
    public static void main(String[] arg) {
    for (int i = 0; i < 5; i++) {
    Runnable r = new MyRunnable();
    Thread t = new Thread(r);
    t.start();
    }
    System.out.println("Parent: " + Thread.currentThread().getId());
    }
    }

输出结果如下:
Child: 8
Child: 9
Child: 10
Child: 11
Parent: 1
Child: 12
这里不能直接调用run方法,因为这样不会创建新的线程:

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public class MyRunnable implements Runnable {
@Override
public void run() {
System.out.println("Child: " + Thread.currentThread().getId());
}
public static void main(String[] arg) {
for (int i = 0; i < 5; i++) {
Runnable r = new MyRunnable();
// Thread t = new Thread(r);
// t.start();
r.run();
}
System.out.println("Parent: " + Thread.currentThread().getId());
}
}

输出结果如下:
Child: 1
Child: 1
Child: 1
Child: 1
Child: 1
Parent: 1
可以看到id都是一样的,也就是这里没有创建新的线程.

继承Thread类

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class MyThread extends Thread {
public void run() {
task code
}
}

完整例子如下:

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public class MyThread extends Thread {
@Override
public void run() {
System.out.println("Child: " + Thread.currentThread().getId());
}
public static void main(String[] arg) {
for (int i = 0; i < 5; i++) {
Thread t = new MyThread();
t.start();
}
System.out.println("Parent: " + Thread.currentThread().getId());
}
}

输出结果如下:
Child: 8
Child: 9
Child: 10
Child: 11
Parent: 1
Child: 12
这里不能直接调用t.run(),因为这样不会创建新的线程

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public class MyThread extends Thread {
@Override
public void run() {
System.out.println("Child: " + Thread.currentThread().getId());
}
public static void main(String[] arg) {
for (int i = 0; i < 5; i++) {
Thread t = new MyThread();
// t.start();
t.run();
}
System.out.println("Parent: " + Thread.currentThread().getId());
}
}

结果如下:
Child: 1
Child: 1
Child: 1
Child: 1
Child: 1
Parent: 1
可以看到id都是一样的。
查看Thread类的源码就会发现问题的所在.

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public synchronized void start() {
/**
* This method is not invoked for the main method thread or "system"
* group threads created/set up by the VM. Any new functionality added
* to this method in the future may have to also be added to the VM.
*
* A zero status value corresponds to state "NEW".
*/
if (threadStatus != 0)
throw new IllegalThreadStateException();

/* Notify the group that this thread is about to be started
* so that it can be added to the group's list of threads
* and the group's unstarted count can be decremented. */
group.add(this);

boolean started = false;
try {
start0();
started = true;
} finally {
try {
if (!started) {
group.threadStartFailed(this);
}
} catch (Throwable ignore) {
/* do nothing. If start0 threw a Throwable then
it will be passed up the call stack */
}
}
}

private native void start0();

在start方法中调用native方法start0(),虽然看不到它的具体实现,但可以推测这里创建了新的线程,然后调用run方法。而run方法中,则没有创建线程相关的代码

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public void run() {
if (target != null) {
target.run();
}
}

关于两种方法的区别,可以看http://stackoverflow.com/questions/541487/implements-runnable-vs-extends-thread, 推荐使用实现Runnable接口的方法。

文章目錄
  1. 1. 实现Runnable接口
  2. 2. 继承Thread类