实现Runnable接口方式

package com.roocon.thread.t2;

public class Demo2 implements Runnable {
    @Override
    public void run() {
        while(true){
            System.out.println("thread running...");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        Thread thread = new Thread(new Demo2());
        thread.start();
    }
}

输出结果：

thread running...
thread running...
thread running...
thread running...

源码解读：

1.Thread类：根据以下代码知道，我们传入的runnable参数最后是赋值给了Thread类的属性target。

public Thread(Runnable target) {
        init(null, target, "Thread-" + nextThreadNum(), 0);
    }
private void init(ThreadGroup g, Runnable target, String name,
                      long stackSize) {
        init(g, target, name, stackSize, null);
    }
private void init(ThreadGroup g, Runnable target, String name,
                      long stackSize, AccessControlContext acc) {
        if (name == null) {
            throw new NullPointerException("name cannot be null");
        }

        this.name = name.toCharArray();

        Thread parent = currentThread();
        SecurityManager security = System.getSecurityManager();
        if (g == null) {
            /* Determine if it's an applet or not */

            /* If there is a security manager, ask the security manager
               what to do. */
            if (security != null) {
                g = security.getThreadGroup();
            }

            /* If the security doesn't have a strong opinion of the matter
               use the parent thread group. */
            if (g == null) {
                g = parent.getThreadGroup();
            }
        }

        /* checkAccess regardless of whether or not threadgroup is
           explicitly passed in. */
        g.checkAccess();

        /*
         * Do we have the required permissions?
         */
        if (security != null) {
            if (isCCLOverridden(getClass())) {
                security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
            }
        }

        g.addUnstarted();

        this.group = g;
        this.daemon = parent.isDaemon();
        this.priority = parent.getPriority();
        if (security == null || isCCLOverridden(parent.getClass()))
            this.contextClassLoader = parent.getContextClassLoader();
        else
            this.contextClassLoader = parent.contextClassLoader;
        this.inheritedAccessControlContext =
                acc != null ? acc : AccessController.getContext();
        this.target = target;//赋给了Thread的属性target
        setPriority(priority);
        if (parent.inheritableThreadLocals != null)
            this.inheritableThreadLocals =
                ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
        /* Stash the specified stack size in case the VM cares */
        this.stackSize = stackSize;

        /* Set thread ID */
        tid = nextThreadID();
    }

2.调用start方法启动线程

thread.start();

3.Thread类就去找run方法：

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

4.于是，调用了我们runnable接口中重写的run方法。输出：

thread running...
thread running...
thread running...
thread running...