Runnable和Thread

 1 /**
 2  * The <code>Runnable</code> interface should be implemented by any
 3  * class whose instances are intended to be executed by a thread. The
 4  * class must define a method of no arguments called <code>run</code>.
 5  * <p>
 6  * This interface is designed to provide a common protocol for objects that
 7  * wish to execute code while they are active. For example,
 8  * <code>Runnable</code> is implemented by class <code>Thread</code>.
 9  * Being active simply means that a thread has been started and has not
10  * yet been stopped.
11  * <p>
12  * In addition, <code>Runnable</code> provides the means for a class to be
13  * active while not subclassing <code>Thread</code>. A class that implements
14  * <code>Runnable</code> can run without subclassing <code>Thread</code>
15  * by instantiating a <code>Thread</code> instance and passing itself in
16  * as the target.  In most cases, the <code>Runnable</code> interface should
17  * be used if you are only planning to override the <code>run()</code>
18  * method and no other <code>Thread</code> methods.
19  * This is important because classes should not be subclassed
20  * unless the programmer intends on modifying or enhancing the fundamental
21  * behavior of the class.
22  *
23  * @author  Arthur van Hoff
24  * @see     java.lang.Thread
25  * @see     java.util.concurrent.Callable
26  * @since   JDK1.0
27  */

//Thread
Thread t = new Thread() {
    public void run() {
        System.out.println("Thread");
    }
};
t.start();

//Runnable
Runnable r=new Runnable() {
    @Override
    public void run() {
        System.out.println("Runnable");
    }
};
Thread t=new Thread(r);
t.start();

//实现Runnable方式调用构造函数
public Thread(Runnable target) {
        init(null, target, "Thread-" + nextThreadNum(), 0);
}

//继承Thread方式调用构造函数
public Thread() {
        init(null, null, "Thread-" + nextThreadNum(), 0);
}

//最终调用初始化函数
private void init(ThreadGroup g, Runnable target, String name,
                      long stackSize, AccessControlContext acc,
                      boolean inheritThreadLocals) {
        if (name == null) {
            throw new NullPointerException("name cannot be null");
        }

        this.name = name;

        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;
        setPriority(priority);
        if (inheritThreadLocals && 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();
}


//Thread类的run方法
@Override

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