Java多线程02-启动线程

java启动线程有两个方法:

• start()
• run()

public class StartAndRunMethod {
    public static void main(String[] args) {
        Runnable runnable = () -> {
            System.out.println(Thread.currentThread().getName());
        };
        runnable.run();

        new Thread(runnable).start();
    }
}

start()方法原理

start方法就是去启动新线程，执行流程如下：

• 检查线程状态，只有NEW状态下的线程才能继续，否则会抛出IllegalThreadStateException异常。
• 加入到线程组。
• 调用start0()方法启动线程。

    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 */
            }
        }
    }

run()方法原理

    @Override
    public void run() {
        if (target != null) {
            target.run();
        }
    }

run()方法会根据传入的对象执行不同结果

小结

start()才是真正启动一个线程，而如果直接调用run()，那么run只是一个普通的方法而已，和线程的生命周期没有任何关系。