【Java多线程】Thread和Runnable创建新线程区别
这是一道面试题，创建多线程时，使用继承Thread类和实现Runnable接口有哪些区别呢？
一、Thread先来看看Thread类和其中的start()方法
class Thread implements Runnable{.....}
// 可见，Thread类实现了Runnable接口
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 */
}
}
}
其中，start0()是一个native方法，在操作系统层面开启一个新线程。继承Thread类后，重写run()方法，则调用start()方法会执行子类的run()方法。
class MyThread extends Thread{
private int count = 10;
@Override
public void run() {
while(count > 0)
System.out.println(count--);
}
}
public class Main{
public static void main(String[] args) {
// Thread类中有start()方法，调用父类start()执行子类run()
new MyThread().start();
new MyThread().start();
new MyThread().start();
}
}
二、Runnable
相同代码改成实现Runnable接口
class MyThread implements Runnable{
private int count = 10;
@Override
public void run() {
while(count > 0)
System.out.println(count--);
}
}
public class Solution {
public static void main(String[] args) {
Runnable myThread = new MyThread();
new Thread(myThread).start();
new Thread(myThread).start();
new Thread(myThread).start();
}
}
显然，实现Runnable接口时，3个线程共享了count变量，而在继承Thread类时，每个线程各有一个count，没有共享。在秒杀、抢票等场景中，显然实现Runnable接口符合业务逻辑。
另外，线程池中只能接受Runnable或Callable的线程。
继承Thread：
new MyThread().start();
实现Runnable
Runnable myThread = new MyThread();
new Thread(myThread).start();
2、继承与接口的区别
Java中只能单继承，但接口可以实现多个，Runnable实现方式更加灵活。
3、方便共享资源Runnable方式实现的线程方便资源共享，多个线程共同操作同一变量，符合大多数业务逻辑。
4、线程池相关线程池只接受Runnable、Callable类线程，不能直接放入继承Thread的类。
Steven_L_
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作者：Steven_L_
