Java中使用Thread类和Runnable接口实现多线程的区别

public class ThreadDemo{
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            //创建并启动由继承Thread类创建的线程
            new Thread(new MyThread(),"Thread"+i).start();
             //创建并启动由实现Runnable接口创建的线程
            new Thread(new Runner(),"Thread"+i).start();
        }
    }
}

//继承Thread类
class MyThread extends Thread{
    //重写run方法
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"由继承Thread创建");
    }
}

//实现Runnable接口
class Runner implements Runnable{
    //实现run方法
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"有实现Runnable接口创建");
    }
}

//Thread类继承了Runnable类
public class Thread implements Runnable {}
//Thread的构造函数调用了init方法
public Thread(Runnable target) {
        init(null, target, "Thread-" + nextThreadNum(), 0);
}
//init调用了静态方法init
private void init(ThreadGroup g, Runnable target, String name,
                      long stackSize) {
        init(g, target, name, stackSize, null, true);
}
//再看静态方法init
private void init(ThreadGroup g, Runnable target, String name,
                  long stackSize, AccessControlContext acc,
                  boolean inheritThreadLocals) {
        ...
        //私有Runnable实例
        this.target = target;
        ...
}
//再看一下Runnable方法
@Override
public void run() {
    if (target != null) {
        target.run();
    }
}