线程中start和run方法的区别

先说java中实现多线程常用的两种方式：
   1：继承Thread类，并重写run()方法
   2：实现Runnable接口，实现run方法
实际上Thread类也是实现了Runnable接口

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public class Thread implements Runnable {   ........ ｝

而Runnable接口只定义了一个run方法

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@FunctionalInterface public interface Runnable {     /**      * When an object implementing interface <code>Runnable</code> is used      * to create a thread, starting the thread causes the object's      * <code>run</code> method to be called in that separately executing      * thread.      * <p>      * The general contract of the method <code>run</code> is that it may      * take any action whatsoever.      *      * @see     java.lang.Thread#run()      */     public abstract void run(); }

我们需要实现的多线程业务逻辑，都需要在run方法内实现。

而start()是Thread中定义的方法，以下是start()方法的源码

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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 */             }         }     }

start()通过调用本地native方法start0来启动一个线程，本地方法内最终会调用run方法，这样就可以实现在另一个线程中运行我们需要的代码。
而单独运行run()方法，就跟我们调用普通接口实现方法一样了，并不会启动新的线程.
总结：
1、start()方法运行时，本地启动新的线程，线程中会调用run方法，程序不需要等待run方法执行完毕再执行后面的程序;

2、run()方法是我们编写需要新的线程执行代码的方法，单独运行是不会有多线程效果的。

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