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Android Thread

阅读更多
创建新线程的常用方式:

   1. 直接使用Thread创建
       Thread thread = new Thread();
       thread.start();
  2. 扩展java.lang.Thread类
       Thread类的定义public class Threadextends Object implements Runnable(){…}
扩展Thread类的实质其实也是实现Runnable接口,只不过Thread类继承了Object类方法
  3. 实现Runnable接口

具体代码:

  1. 扩展java.lang.Thread类
public class test3_4  extends Activity  {
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        MyThread myThread = new MyThread();
        myThread.start();
    }
    class MyThread extends Thread{

         public void run() {
            System.out.println("zz");
        }  
   }
}

注:看见网上有人举这个例子
        MyThread myThread = new MyThread();
        myThread.start();
        myThread.start();
        myThread.start();
我在模拟器上测试了运行不过,不能得到预期结果。不知道为什么!runnable的也不行!

2. 实现Runnable接口
public class test3_4  extends Activity {
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        MyThread myThread = new MyThread();
        new Thread(myThread).start();
    }
    class MyThread implements Runnable{
        public void run() {
            System.out.println("zz");
        }   
    }
}

或者

public class test3_4  extends Activity implements OnClickListener, Runnable{
     private Button button;
     private TextView text;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button = (Button)findViewById(R.id.button);
        text = (TextView)findViewById(R.id.text);
        button.setOnClickListener(this);
    }

    public void onClick(View v) {
        Thread thread = new Thread(this);
        thread.start();
    }

    public void run() {
        System.out.println("zz");
    }
}

经典实例:

多个窗口一起卖火车票问题。假设有3个窗口同时售票,共有10张火车票代售。启动三个线程卖共同的10张票。

1. 使用下面的代码试图实现功能

public class test3_5  extends Activity implements OnClickListener{
     private Button button;
     private TextView text;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button = (Button)findViewById(R.id.button);
        text = (TextView)findViewById(R.id.text);
        button.setOnClickListener(this);
    }

    public void onClick(View v) {
        MyThread myThread1 = new MyThread();
        MyThread myThread2= new MyThread();
        MyThread myThread3 = new MyThread();
        myThread1.start();
        myThread2.start();
        myThread3.start();
    }
    class MyThread extends Thread{
        private int tickets = 10;
        public void run() {
            for(int i = 0; i< 200; i++){
                if(tickets > 0)
                {
                    System.out.println(Thread.currentThread().getName() + "==>" + tickets--);
                }
            }
        }
    }
}

运行结果:

05-11 08:24:09.426: INFO/System.out(6331): Thread-8==>10
05-11 08:24:09.457: INFO/System.out(6331): Thread-8==>9
05-11 08:24:09.526: INFO/System.out(6331): Thread-8==>8
05-11 08:24:09.548: INFO/System.out(6331): Thread-8==>7
05-11 08:24:09.556: INFO/System.out(6331): Thread-8==>6
05-11 08:24:09.556: INFO/System.out(6331): Thread-8==>5
05-11 08:24:09.576: INFO/System.out(6331): Thread-8==>4
05-11 08:24:09.597: INFO/System.out(6331): Thread-10==>10
05-11 08:24:09.606: INFO/System.out(6331): Thread-10==>9
05-11 08:24:09.606: INFO/System.out(6331): Thread-10==>8
05-11 08:24:09.648: INFO/System.out(6331): Thread-8==>3
05-11 08:24:09.656: INFO/System.out(6331): Thread-9==>10
05-11 08:24:09.656: INFO/System.out(6331): Thread-9==>9
05-11 08:24:09.666: INFO/System.out(6331): Thread-8==>2
05-11 08:24:09.666: INFO/System.out(6331): Thread-8==>1
05-11 08:24:09.686: INFO/System.out(6331): Thread-9==>8
05-11 08:24:09.686: INFO/System.out(6331): Thread-10==>7
05-11 08:24:09.686: INFO/System.out(6331): Thread-10==>6
05-11 08:24:09.737: INFO/System.out(6331): Thread-9==>7
05-11 08:24:09.746: INFO/System.out(6331): Thread-9==>6
05-11 08:24:09.746: INFO/System.out(6331): Thread-9==>5
05-11 08:24:09.766: INFO/System.out(6331): Thread-10==>5
05-11 08:24:09.776: INFO/System.out(6331): Thread-10==>4
05-11 08:24:09.776: INFO/System.out(6331): Thread-10==>3
05-11 08:24:09.776: INFO/System.out(6331): Thread-10==>2
05-11 08:24:09.846: INFO/System.out(6331): Thread-9==>4
05-11 08:24:09.846: INFO/System.out(6331): Thread-9==>3
05-11 08:24:09.846: INFO/System.out(6331): Thread-9==>2
05-11 08:24:09.886: INFO/System.out(6331): Thread-9==>1
05-11 08:24:09.886: INFO/System.out(6331): Thread-10==>1

分析:

运行结果与预期不一致,分析可以看出3个线程各种卖各自的10张票,而不是共同的10张票。

在上面的代码中,只能保证:每个线程都将启动,每个线程都将运行直到完成。一系列线程以某种顺序启动并不意味着将按该顺序执行。对于任何一组启动的线程来说,调度程序不能保证其执行次序,持续时间也无法保证。

2. 只修改onClick里面的代码,并分析运行结果

public void onClick(View v) {
    //实例化线程对象
    MyThread myThread = new MyThread();
    new Thread(myThread, "窗口1").start();
    new Thread(myThread, "窗口2").start();
    new Thread(myThread, "窗口3").start();
}

运行结果:

05-11 08:41:50.946: INFO/System.out(6790): 窗口2==>10
05-11 08:41:50.956: INFO/System.out(6790): 窗口2==>8
05-11 08:41:50.986: INFO/System.out(6790): 窗口1==>9
05-11 08:41:50.996: INFO/System.out(6790): 窗口1==>5
05-11 08:41:51.006: INFO/System.out(6790): 窗口1==>4
05-11 08:41:51.018: INFO/System.out(6790): 窗口2==>6
05-11 08:41:51.018: INFO/System.out(6790): 窗口2==>3
05-11 08:41:51.026: INFO/System.out(6790): 窗口2==>2
05-11 08:41:51.036: INFO/System.out(6790): 窗口1==>1
05-11 08:41:51.046: INFO/System.out(6790): 窗口3==>7

分析:

我认为此处3个窗口已经是在卖共同的10张票了,只不过由于没有进行线程同步才造成数据混乱。

线程的同步是为了防止多个线程访问一个数据对象时,对数据造成的破坏。

3. 下面继续修改代码,验证我刚得猜测。

public void onClick(View v) {
    //实例化线程对象
    MyThread myThread = new MyThread();
    new Thread(myThread, "窗口1").start();
    new Thread(myThread, "窗口2").start();
    new Thread(myThread, "窗口3").start();
}

class MyThread extends Thread{
    private int tickets = 10;
    public void run() {
        for(int i = 0; i< 200; i++){
                sell();
        }
    }
    public synchronized  void sell(){
            if(tickets > 0)
            {
                System.out.println(Thread.currentThread().getName() + "==>" + tickets--);
            }
    }
}

运行结果:

05-11 08:53:31.986: INFO/System.out(7116): 窗口1==>10
05-11 08:53:32.006: INFO/System.out(7116): 窗口1==>9
05-11 08:53:32.016: INFO/System.out(7116): 窗口1==>8
05-11 08:53:32.066: INFO/System.out(7116): 窗口1==>7
05-11 08:53:32.086: INFO/System.out(7116): 窗口1==>6
05-11 08:53:32.106: INFO/System.out(7116): 窗口1==>5
05-11 08:53:32.106: INFO/System.out(7116): 窗口1==>4
05-11 08:53:32.126: INFO/System.out(7116): 窗口1==>3
05-11 08:53:32.146: INFO/System.out(7116): 窗口1==>2
05-11 08:53:32.146: INFO/System.out(7116): 窗口1==>1

分析:

一个对象只有一个锁。所以,如果一个线程获得该锁,就没有其他线程可以获得锁,直到第一个线程释放(或返回)锁。这也意味着任何其他线程都不能进入该对象上的synchronized方法或代码块,直到该锁被释放。

释放锁是指持锁线程退出了synchronized同步方法或代码块。

上述代码没有Thread.sleep(10),换句话说线程一一直处于运行状态,没有释放锁,没有给其他线程运行的机会。

4. 根据上述分析,修改代码如下:

public void onClick(View v) {
        //实例化线程对象
        MyThread myThread = new MyThread();
        new Thread(myThread, "窗口1").start();
        new Thread(myThread, "窗口2").start();
        new Thread(myThread, "窗口3").start();
    }
    class MyThread extends Thread{
        private int tickets = 10;
        public void run() {
            for(int i = 0; i< 200; i++){
                try{
                    sell();
                    Thread.sleep(10);
                }catch (InterruptedException e) {
                    System.out.println("我被打断了" + Thread.currentThread().getName());
                    e.printStackTrace();
                }

            }
        }
        public synchronized  void sell(){
                if(tickets > 0)
                {
                    System.out.println(Thread.currentThread().getName() + "==>" + tickets--);
                }
        }
    }

运行结果:

05-11 09:17:07.496: INFO/System.out(7898): 窗口1==>10
05-11 09:17:07.528: INFO/System.out(7898): 窗口1==>9
05-11 09:17:07.546: INFO/System.out(7898): 窗口1==>8
05-11 09:17:07.577: INFO/System.out(7898): 窗口1==>7
05-11 09:17:07.626: INFO/System.out(7898): 窗口3==>6
05-11 09:17:07.626: INFO/System.out(7898): 窗口2==>5
05-11 09:17:07.636: INFO/System.out(7898): 窗口1==>4
05-11 09:17:07.646: INFO/System.out(7898): 窗口2==>3
05-11 09:17:07.646: INFO/System.out(7898): 窗口1==>2
05-11 09:17:07.656: INFO/System.out(7898): 窗口3==>1

分析:

此次得出的正是我们想要的结果!O(∩_∩)O~

5. 使用实现Runnable接口的方法重新实现上述功能

public void onClick(View v) {
        //实例化线程对象
        MyThread myThread = new MyThread();
        new Thread(myThread, "窗口1").start();
        new Thread(myThread, "窗口2").start();
        new Thread(myThread, "窗口3").start();
    }
    class MyThread implements Runnable{
        private int tickets = 10;
        public void run() {
            for(int i = 0; i< 200; i++){
                try{
                    sell();
                    Thread.sleep(10);
                }catch (InterruptedException e) {
                    System.out.println("我被打断了" + Thread.currentThread().getName());
                    e.printStackTrace();
                }

            }
        }
        public synchronized  void sell(){
                if(tickets > 0)
                {
                    System.out.println(Thread.currentThread().getName() + "==>" + tickets--);
                }
        }

关于线程的理解个人推荐一篇非常棒的文章,里面对java线程进行的详细的总结,仔细阅读必有收获!

[url]http://lavasoft.blog.51cto.com/62575/27069/
[/url]
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