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
[Java] 纯文本查看 复制代码?
| 123 | public class Thread implements Runnable { ........｝ |
而Runnable接口只定义了一个run方法
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| 010203040506070809101112131415 | @FunctionalInterfacepublic 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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| 01020304050607080910111213141516171819202122232425262728293031 | 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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