模板设计模式在Thread的应用

       作为一名java程序员，创建线程是工作中经常干的事情，也是面试中经常被提问的问题。大家都知道java中创建线程有两种最基本的方式：

1. 创建Thread类；
2. 实现runnable借口；

这两种方式有一个共同点就是我们的业务逻辑必须要实现run()这个方法,然后我们调用start()方法来启动线程。跟踪Thread的start()方法源码我们可以看到：

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()方法调用了一个start0()方法,而start0()方法源码如下：

 private native void start0();

    /**
     * If this thread was constructed using a separate
     * Runnable run object, then that
     * Runnable object's run method is called;
     * otherwise, this method does nothing and returns.
     * 

     * Subclasses of Thread should override this method.
     *
     * @see     #start()
     * @see     #stop()
     * @see     #Thread(ThreadGroup, Runnable, String)
     */
    @Override
    public void run() {
        if (target != null) {
            target.run();
        }
    }

start0是一个native修饰的方法，而且它调用了run(),其实一点从设计模式上不能理解，这里用到的就是一个简单的模板模式，目的就是为了让业务的逻辑和线程的逻辑分离。以下是模板模式模拟线程的实现，希望有助于理解模板模式在Thread中的应用

/**
 * Description
 * 

 * 
 * DATE 2018/10/26.
 *
 * @author caichengzhang.
 */
public class Template {

    public Template() {
    }

    public final void start(){
        System.out.println("stat方法启动！");
        run();
        System.out.println("start方法结束！");
    }

    public void run(){}

    public static void main(String[] args) {

        Template template = new Template(){
            @Override
            public void run() {
                System.out.println("run方法开始运行！");
            }
        };

        template.start();
    }

}

运行结果：

stat方法启动！
run方法开始运行！
start方法结束！