Java多线程应注意的细节之一

我们知道在Java中有两种方式可以实现Java的多线程，一种是通过继续Thread类并重写run()方法；另一种是通过实现Runnable接口。废话少说，先跑下面的例子先：

package com.kkoolerter.thread;

public class ThreadTest {

public static void main(String[] args) {
new ThreadA("threadA").start();
new Thread(new RunnableA("runnable")).start();
new RunnableA("runnableA").run();
new RunnableA("runnableB").run();
new ThreadA("threadB").run();
new ThreadA("threadC").run();
System.out.println("[threadC] finished executing.");
}

}

class ThreadA extends Thread{

public ThreadA(String name){
this.setName(name);
}
public ThreadA(Runnable runnable){
super(runnable);
}
@Override
public void run() {
System.out.println("Thread:["+this.getName()+"]begine");
System.out.println(this.getName()+" current thread is:["+Thread.currentThread().getName()+"]");
for(long i = 0;i<9999999;i++);
System.out.println("Thread:["+this.getName()+"]end\n");
}

}

class RunnableA implements Runnable{
private String name;
public RunnableA(String name){
this.name = name;
}
@Override
public void run() {
System.out.println("Thread:["+this.name+"]begine");
System.out.println(this.name+" current thread is:["+Thread.currentThread().getName()+"]");
for(long i = 0;i<9999999;i++);
System.out.println("Thread:["+this.name+"]end\n");
}

}

上述例子可能的一个输出结果：

Thread:[threadA]begine
threadA current thread is:[threadA]
Thread:[runnableA]begine
runnableA current thread is:[main]
Thread:[threadA]end

Thread:[runnable]begine
runnable current thread is:[Thread-1]
Thread:[runnableA]end

Thread:[runnableB]begine
runnableB current thread is:[main]
Thread:[runnable]end

Thread:[runnableB]end

Thread:[threadB]begine
threadB current thread is:[main]
Thread:[threadB]end

Thread:[threadC]begine
threadC current thread is:[main]
Thread:[threadC]end

[threadC] finished executing.

从运行的结果可以知道，如果直接调用Thread或Runnable接口实现类的run()方法，那么它将在main方法线程里按顺序运行，相当于在main()方法里调用一个普通方法。所以在实现多线程时，应该调用Thread的start()方法，因为调用start()方法使该线程开始执行；Java 虚拟机调用该线程的

run

方法。结果是两个线程并发地运行；当前线程（从调用返回给

start

方法）和另一个线程（执行其

run

方法）。

注意：多次启动一个线程是非法的。特别是当线程已经结束执行后，不能再重新启动。本文出自 “有思想的代码” 博客，请务必保留此出处http://wujuxiang.blog.51cto.com/2250829/427205