Java线程Run和Start的区别

2019-02-17 01:52:05来源：博客园阅读 ()

先上结论：run只是Thread里面的一个普通方法，start是启动线程的方法。何以见得呢？可以执行下面的代码看看run和start的区别：

package com.basic.thread;

/**
 * @author zhangxingrui
 * @create 2019-02-16 20:12
 **/
public class TestRunAndStart {

    private static void sayHello(){
        System.out.println("hello, world");
    }

    public static void main(String[] args) {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                sayHello();
                System.out.println("Current thread: " + Thread.currentThread().getName());
            }
        });

        thread.run();
        thread.start();
    }

}

　　执行结果：

　　由此可以看到子线程是由start来启动的，里面调用了run，所以打印出来的是子线程的name。

　　另外也可以从start方法的底层代码看到，首先进入start方法里面

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 */
            }
        }
    }