java线程学习之线程创建

线程是程序控制的一个内部数据流。线程的状态转化如下

或者

在java中创建线程有两种方式：

1.实现runnable接口（这个比较好，推荐这个。原因是：用的时候比较灵活，相比较继承Thread类，用接口来实现可以减少资源使用，比较继承也是一种宝贵资源，毕竟Java是单继承多实现）

2.继承Thread类（Thread类实现了Runnable方法）

利用Runnable接口启动线程的方法是：先创建Runnable接口的实现类，然后将实现类的实例作为参数传给Thread的构造方法，最后调用start方法。

利用继承Thread类来启动线程的方法是：先创建Thread类的子类，然后创建子类的实例，最后调用start方法。

两种方式均是利用Thread类的Start方法。

 /**
      * Causes this thread to begin execution; the Java Virtual Machine
      * calls the <code>run</code> method of this thread.
      * <p>
      * The result is that two threads are running concurrently: the
      * current thread (which returns from the call to the
      * <code>start</code> method) and the other thread (which executes its
      * <code>run</code> method).
      * <p>
      * It is never legal to start a thread more than once.
      * In particular, a thread may not be restarted once it has completed
      * execution.
      *
      * @exception  IllegalThreadStateException  if the thread was already
      *               started.
      * @see        #run()
      * @see        #stop()
      */
     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 */
             }
         }
     }

jdk中Thread类的start方法

例子一：实现runnable接口

 package com.song.test;

 public class TestRunnable implements Runnable {
     public void run() {
         System.out.println("线程启动....");
     }
     public static void main(String[] args) {
         System.out.println("测试线程一....");
         TestRunnable test=new TestRunnable(); //创建实现类的实例
         Thread t1=new Thread(test);   //将实现类的实例作为参数传给Thread的构造方法
         t1.start();//调用start方法启动线程
     }
 }

运行结果：

java的jdk1.6对java.lang.Runnable的解释

2例子二：继承Thread类

 package com.song.test;

 public class TestThread01 extends Thread {
     public static void main(String[] args) {
         System.out.println("开始执行");
         TestThread01 test = new TestThread01();
         test.start();
     }

     @Override
     public void run() {
         System.out.println("用继承Thread的线程已启动");
     }
 }

结果为：

使用的jdk1.6的解释为：

关于线程终止：是指除守护线程以外的线程全部终止，守护线程是执行后台作业的线程。当进入main方法中执行程序时就已经启动了主线程，在主线程执行过程中创建了另一个线程 A,且利用start（）方法启动它，这时是启动两个线程，main线程和A线程。当main方法代码执行完毕，即主线程才为终止。但如果此时线程A仍在执行中，即A线程仍在运行状态不能说此时程序终止，也就是说所以程序均终止后，程序才能终止。

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