Java多線程(1)

多線程的機制是指可以同時運行多個程序塊，是程序運行的效率變的更高。

一、兩種多線程的實現方式

如果要在類裏要激活線程，必須先做好下面兩個準備：
    1、線程必須擴展子Thread類，使自己成爲它的子類

    2、線程的處理必須編寫在run()方法裏面

繼承Thread類來實現多線程，其基本語法如下

class 類名稱 extends Thread{
       屬性...
       方法...
       修飾符 run(){
          other code
       }
}

範例1：

public class Test2 {

    public static void main(String args[]){

            TestThread t1 = new TestThread("A");

            TestThread t2 = new TestThread("B");

            t1.start();

            t2.start();

    }

}

class TestThread extends Thread{

    private String name;

    public TestThread(){

    }

    public TestThread(String name){

        this.name = name;

    }

    public void run(){

        for(int i=0;i<10;i++){

             System.out.println(name + " is running");

        }

    }

}

運行結果：

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

B is running

A is running

通過實現Runnable接口實現多線程，基本語法如下

class 類名稱 implements Runnable{
       屬性...
       方法...
       修飾符 run(){
          other code
       }
}

範例2：

public class Test3 {

    public static void main(String args[]){

            TestThread t1 = new TestThread("Thread A");

            Thread t11 = new Thread(t1);

            TestThread t2 = new TestThread("Thread B");

            Thread t22 = new Thread(t2);

            t11.start();

            t22.start();

    }

}

class TestThread implements Runnable{

    private String name;

    public TestThread(){

    }

    public TestThread(String name){

        this.name = name;

    }

    public void run(){

        for(int i=0;i<10;i++){

             System.out.println(name + " is running");

        }

    }

}

運行結果：

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

Thread B is running

Thread A is running

二、Thread和Runnable的區別：

如果一個類繼承Thread，則不適合資源共享。但是如果實現了Runable接口的話，則很容易的實現資源共享

範例1：

public class Test4 {

    public static void main(String args[]){

            TestThread t1 = new TestThread("A");

            TestThread t2 = new TestThread("B");

            t1.start();

            t2.start();

    }

}

class TestThread extends Thread{

    private String name;

    private int count = 5;

    public TestThread(){

    }

    public TestThread(String name){

        this.name = name;

    }

    public void run(){

        for(int i=0;i<10;i++){

             if(count > 0){

                 System.out.println("count = "+count--);

             }

        }

    }

}

運行結果：

count = 5

count = 5

count = 4

count = 4

count = 3

count = 3

count = 2

count = 2

count = 1

count = 1

沒有能夠實現資源共享，那麼用Ruannable接口呢，請看下面...........

範例2：
public class Test5 {

    public static void main(String args[]){

            TestThread t1 = new TestThread();

            Thread t11 = new Thread(t1,"1#");

            Thread t22 = new Thread(t1,"2#");

            t11.start();

            t22.start();

    }

}

class TestThread implements Runnable{

    private String name;

    private int count = 5;

    public TestThread(){

    }

    public TestThread(String name){

        this.name = name;

    }

    public void run(){

        for(int i=0;i<10;i++){

             if(count>0){

                 System.out.println(Thread.currentThread().getName()+" count = "+count--);

             }

        }

    }

}

運行結果：
2# count = 4

1# count = 5

2# count = 3

1# count = 2

2# count = 1

可以看出實現了資源共享

總結如下：

實現Runnable接口比繼承Thread類所具有的優勢：

   1）：適合多個相同的程序代碼的線程去處理同一個資源

   2）：可以避免java中的單繼承的限制

   3）：增加程序的健壯性，代碼可以被多個線程共享，代碼和數據獨立。

三、線程中的一些操作方法

1、取得和設置線程的名稱

getName()

範例1：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         mTestThread.start();

         String ThreadName = Thread.currentThread().getName();

         System.out.println("Thread name is "+ThreadName);

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         System.out.println("TestThread name is "+ThreadName);

     }

}

運行結果：

Thread name is main

TestThread name is Thread-0

setName()

範例2：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         mTestThread.setName("NewName");

         mTestThread.start();

         String ThreadName = Thread.currentThread().getName();

         System.out.println("Thread name is "+ThreadName);

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         System.out.println("TestThread name is "+ThreadName);

     }

}

運行結果：

Thread name is main

TestThread name is NewName

2、判斷線程是否啓動

isAlive()

範例3：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         System.out.println("Before start the thread:isAlive = "+mTestThread.isAlive());

         mTestThread.start();

         System.out.println("After start the thread:isAlive = "+mTestThread.isAlive());

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         System.out.println("TestThread name is "+ThreadName);

     }

}

3、線程的強制執行

不使用join()

範例4：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         mTestThread.start();

         for(int i=0;i<5;i++){

             System.out.println("mai thread is running: "+i);

         }

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         for(int i=0;i<5;i++){

             System.out.println(ThreadName+" is runnging: "+i);

         }

     }

}

運行結果：

mai thread is running: 0

Thread-0 is runnging: 0

mai thread is running: 1

Thread-0 is runnging: 1

mai thread is running: 2

Thread-0 is runnging: 2

mai thread is running: 3

Thread-0 is runnging: 3

mai thread is running: 4

Thread-0 is runnging: 4

使用join()

範例5：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         mTestThread.start();

         for(int i=0;i<5;i++){

             if(i==2){

                try{

                   mTestThread.join();

                }catch(Exception e){

                }

             }

             System.out.println("mai thread is running: "+i);

         }

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         for(int i=0;i<5;i++){

             System.out.println(ThreadName+" is runnging: "+i);

         }

     }

}

運行結果：
mai thread is running: 0

Thread-0 is runnging: 0

mai thread is running: 1

Thread-0 is runnging: 1

Thread-0 is runnging: 2

Thread-0 is runnging: 3

Thread-0 is runnging: 4

mai thread is running: 2

mai thread is running: 3

mai thread is running: 4

可以看到執行完join()之後，就會一直執行Thread-0

4、線程休眠

使用sleep(long millions)來進行休眠

範例6：

import java.util.Date;

import java.text.SimpleDateFormat;

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         mTestThread.start();

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

         System.out.println(df.format(new Date()));

         for(int i=0;i<5;i++){

             try{

                Thread.sleep(3000);

             }catch(Exception e){

                e.printStackTrace();

             }

             System.out.println(ThreadName+" is runnging: "+i);

             System.out.println(df.format(new Date()));

         }

     }

}

運行結果：每隔3秒輸出一個打印
2014-05-09 11:27:51

Thread-0 is runnging: 0

2014-05-09 11:27:54

Thread-0 is runnging: 1

2014-05-09 11:27:57

Thread-0 is runnging: 2

2014-05-09 11:28:00

Thread-0 is runnging: 3

2014-05-09 11:28:03

Thread-0 is runnging: 4

2014-05-09 11:28:06

5、線程中斷

使用interrupt()方法來中斷

範例7：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         mTestThread.start();

         try{

           mTestThread.sleep(2000);

         }catch(Exception e){

                e.printStackTrace();

         }

         mTestThread.interrupt();

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

             try{

                Thread.sleep(10000);

                System.out.println("The thread finish sleep");

             }catch(Exception e){

                System.out.println("Sleep is interrupted");

                return;

             }

         System.out.println("The thread finish normally");

     }

}

運行結果：
Sleep is interrupted

6、後臺線程

對Java程序來說，只要還有一個前臺線程在運行，這個進程就不會結束，如果一個進程中只有後臺線程在運行，這個進程就會結束。前臺線程是相對後臺線程而言的。什麼樣的線程是後臺線程呢？如果某個線程對象在啓(調用start()方法)動之前調用了setDaemon(true)方法，這個線程就變成了後臺線程。

範例8：

public class Test {

     public static void main(String args[]){

         TestThread mTestThread = new TestThread();

         TestThread2 mTestThread2 = new TestThread2();

         mTestThread.setDaemon(true);

         mTestThread.start();

         mTestThread2.start();

     }

}

class TestThread extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         while(true){

             System.out.println(ThreadName+" is running");

         }

     }

}

class TestThread2 extends Thread{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         for(int i=0;i<5;i++){

             System.out.println(ThreadName+" is running");

         }

     }

}

在TestThread中的run()中使用了死循環，如果不設置setDaemon(true)方法，那麼該程序將無線循環執行下去，如果使用該方法設爲後臺進程，則運行結果如下：

Thread-0 is running

Thread-1 is running

Thread-0 is running

Thread-1 is running

Thread-0 is running

Thread-1 is running

Thread-0 is running

Thread-1 is running

Thread-0 is running

Thread-1 is running

Thread-0 is running

Thread-0 is running

Thread-0 is running

Thread-0 is running

從以上結果我們可以看到，隨着TestThread2的結束，TestThread也會結束。

7、線程的優先級

  使用setPriority()設置優先級

public class Test {

     public static void main(String args[]){

         Thread mTestThread1 = new Thread(new TestThread(),"A");

         Thread mTestThread2 = new Thread(new TestThread(),"B");

         Thread mTestThread3 = new Thread(new TestThread(),"C");

         mTestThread1.setPriority(1);

         mTestThread1.setPriority(2);

         mTestThread1.setPriority(3);

         mTestThread1.start();

         mTestThread2.start();

         mTestThread3.start();

     }

}

class TestThread implements Runnable{

     public void run(){

         String ThreadName = Thread.currentThread().getName();

         for(int i=0;i<5;i++){

             System.out.println(ThreadName+" is running "+i);

         }

     }

}

運行結果：

C is running 0

A is running 0

B is running 0

A is running 1

C is running 1

A is running 2

B is running 1

B is running 2

A is running 3

C is running 2

A is running 4

B is running 3

C is running 3

B is running 4

C is running 4

並不是優先級越高就先執行，誰先執行還是取決於誰先去的CPU的資源。