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[Java教程]java多线程系列7


本文主要总结在java中停止线程的方法

在java中有以下三种方法可以终止正在运行的线程:

1、使用退出标志

2、使用stop方法强行终止线程,但是不推荐,因为stop和suspend、resume一样都是过时的方法

3、使用interrup方法中断线程

停止不了的线程

本例将使用interrupt方法来停止进程,看看效果:

public class MyThread extends Thread {  @Override  public void run() {    super.run();    for (int i = 0; i < 1234; i++) {      System.out.println("i=" + (i + 1));    }  }}public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(2000);      thread.interrupt();                } catch (InterruptedException e) {      System.out.println("main catch");      e.printStackTrace();    }  }}

可以看出,线程没有停止

判断线程是否是停止状态

在java的SDK中,Thread.java类里提供了两种方法:

(1)this.interrupted():测试当前线程是否已经中断

(2)this.isInterrupted():测试线程是否已经中断

首先看一下interrupted()

实战验证一下:

public class MyThread extends Thread {  @Override  public void run() {    super.run();    for (int i = 0; i < 10000; i++) {      System.out.println("i=" + (i + 1));    }  }}public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(1000);      thread.interrupt();      System.out.println("是否停止1?="+thread.interrupted());      System.out.println("是否停止2?="+thread.interrupted());                } catch (InterruptedException e) {      System.out.println("main catch");      e.printStackTrace();    }    System.out.println("end!");  }}

运行结果如下:

.......................

i=9998
i=9999
i=10000
是否停止1?=false
是否停止2?=false
end!

由于interrupted是测试当前线程,当前线程为main,一直没有中断,所以返回两个false

将代码修改一下:

public class Run {  public static void main(String[] args) {    Thread.currentThread().interrupt();    System.out.println("是否停止1?=" + Thread.interrupted());    System.out.println("是否停止2?=" + Thread.interrupted());    System.out.println("end!");  }}

返回如下信息:

是否停止1?=true
是否停止2?=false
end!

由于interrupted方法有清除状态的功能,所以第二次返回false

再看看isInterrupted()方法

public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(1000);      thread.interrupt();      System.out.println("是否停止1?=" + thread.isInterrupted());      System.out.println("是否停止2?=" + thread.isInterrupted());     } catch (InterruptedException e) {      System.out.println("main catch");      e.printStackTrace();    }    System.out.println("end!");  }}

运行结果:

i=123367
i=123368
是否停止1?=true
是否停止2?=true
i=123369
i=123370
i=123371
i=123372

总结:

(1)this.interrupted():测试当前线程是否已经中断,执行后具有将状态标志清除为false的功能

(2)this.isInterrupted():测试线程是否已经中断,但不清除状态标志

能停止的线程--异常法

可以在线程中用for语句来判断一下线程是否是停止状态,如果是停止状态,则后面的代码不再运行即可

public class MyThread extends Thread {  @Override  public void run() {    super.run();    try {      for (int i = 0; i < 500000; i++) {        if (this.interrupted()) {          System.out.println("已经是停止状态了,我要退出了!");          throw new InterruptedException();        }        System.out.println("i=" + (i + 1));      }      System.out.println("我在for下面");    } catch (InterruptedException e) {      System.out.println("进MyThread.java类run方法中的catch了!");      e.printStackTrace();    }  }}public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(2000);      thread.interrupt();    } catch (InterruptedException e) {      System.out.println("main catch");      e.printStackTrace();    }    System.out.println("end!");  }}

在sleep中停止

如果线程在sleep状态下停止线程,有什么效果呢?

public class MyThread extends Thread {  @Override  public void run() {    super.run();    try {      System.out.println("run begin");      Thread.sleep(200000);      System.out.println("run end");    } catch (InterruptedException e) {      System.out.println("在沉睡中被停止!进入catch!" + this.isInterrupted());      e.printStackTrace();    }  }}public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(200);      thread.interrupt();    } catch (InterruptedException e) {      System.out.println("main catch");      e.printStackTrace();    }    System.out.println("end!");  }}

运行结果:

run begin
end!
在沉睡中被停止!进入catch!false
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at com.wuyudong.test1.MyThread.run(MyThread.java:9)

结果说明如果在sleep状态下停止线程,会进入catch语句,并且清除停止状态值,使之变成false

下面进行相反的操作,修改一下:

public class MyThread extends Thread {  @Override  public void run() {    super.run();    try {      for (int i = 0; i < 100000; i++) {        System.out.println("i=" + (i + 1));      }      System.out.println("run begin");      Thread.sleep(200000);      System.out.println("run end");    } catch (InterruptedException e) {      System.out.println("先停止,再遇到了sleep!进入catch!");      e.printStackTrace();    }  }}public class Run {  public static void main(String[] args) {    MyThread thread = new MyThread();    thread.start();    thread.interrupt();    System.out.println("end!");  }}

运行结果如下:

i=100000
run begin
先停止,再遇到了sleep!进入catch!
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at com.wuyudong.test1.MyThread.run(MyThread.java:12)

能停止的线程--暴力停止

使用stop方法停止线程是十分暴力的

public class MyThread extends Thread {  private int i = 0;  @Override  public void run() {    super.run();    try {      while (true) {        i++;        System.out.println("i=" + i);        Thread.sleep(1000);      }    } catch (InterruptedException e) {      System.out.println("先停止,再遇到了sleep!进入catch!");      e.printStackTrace();    }  }}public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(8000);      thread.stop();    } catch (Exception e) {      e.printStackTrace();    }  }}

运行结果如下:

i=1
i=2
i=3
i=4
i=5
i=6
i=7
i=8

方法stop与异常

调用stop方法的时候会抛出java.lang.ThreadDeath异常,但是通常此异常不需要显式地捕捉

public class MyThread extends Thread {  private int i = 0;  @Override  public void run() {    super.run();    try {      while (true) {        i++;        System.out.println("i=" + i);        Thread.sleep(1000);      }    } catch (InterruptedException e) {      System.out.println("先停止,再遇到了sleep!进入catch!");      e.printStackTrace();    }  }}public class Run {  public static void main(String[] args) {    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(8000);      thread.stop();    } catch (Exception e) {      e.printStackTrace();    }  }}

使用return停止线程

将方法interrupt与return结合使用也能实现停止线程的效果

public class MyThread extends Thread {  private int i = 0;  @Override  public void run() {    super.run();    while(true){      if(this.isInterrupted()){        System.out.println("停止了!");        return;      }      System.out.println("timer="+System.currentTimeMillis());    }  }}public class Run {  public static void main(String[] args) throws InterruptedException{    try {      MyThread thread = new MyThread();      thread.start();      Thread.sleep(2000);      thread.interrupt();    } catch (Exception e) {      e.printStackTrace();    }  }}

运行结果如下:

timer=1452841019023
timer=1452841019023
timer=1452841019023
timer=1452841019023
停止了!