玩转java多线程学习篇四 Thread类的常用API之currentThread,isAlive,sleep,interrupt,isInterrupted,stop

男娘i 2022-06-16 03:57 176阅读 0赞

**前言**

该篇中主要学习Thread类的常用API，currentThread,isAlive,sleep,interrupt,isInterrupted,stop,suspend,resume,yieId,join,wait,notify,notifyAll,start等方法的使用以及详解。

1：currentThread（） 返回正在被调用的线程信息。

public class threadTest {
    	public static void main(String[] args) {
    		System.out.println(Thread.currentThread().getName());
    		Runnable myRunnable  =new MyRunnable();
    		Thread thread = new Thread(myRunnable);
    		thread.start();
    	}
    }

public class MyRunnable  implements Runnable{
    	@Override
    	public void run() {
    		System.out.println("Runnable:"+Thread.currentThread().getName());
    	}
    }

运行结果：main    Runnable:Thread-0  
  
2：isAlive（） 判断当前线程是否处于活动状态，返回boolean

public class threadTest {
    	public static void main(String[] args) throws InterruptedException {
    		System.out.println(Thread.currentThread().getName()+",begin:"+Thread.currentThread().isAlive());
    		Runnable myRunnable  =new MyRunnable();
    		Thread thread = new Thread(myRunnable);
    		System.out.println(thread.getName()+",begin:"+thread.isAlive());
    		thread.start();
    		System.out.println(thread.getName()+",end:"+thread.isAlive());
    	}
    }

public class MyRunnable  implements Runnable{
    	@Override
    	public void run() {
    		System.out.println("Runnable:"+Thread.currentThread().getName()+",isAlive:"+Thread.currentThread().isAlive());
    	}
    }

运行结果：main,begin:true  
Thread-0,begin:false  
Thread-0,end:true  
Runnable:Thread-0,isAlive:true

Thread-0,end打印true是因为MyRunnable线程还没有执行完毕，main线程就已经执行System.out.println(thread.getName()+",end:"+thread.isAlive());这段代码了  
  
如果把他换成如下代码

public class threadTest {
    	public static void main(String[] args) throws InterruptedException {
    		System.out.println(Thread.currentThread().getName()+",begin:"+Thread.currentThread().isAlive());
    		Runnable myRunnable  =new MyRunnable();
    		Thread thread = new Thread(myRunnable);
    		System.out.println(thread.getName()+",begin:"+thread.isAlive());
    		thread.start();
    		Thread.sleep(1000);//睡眠1秒
    		System.out.println(thread.getName()+",end:"+thread.isAlive());
    	}
    }

运行结果：main,begin:true  
Thread-0,begin:false  
Runnable:Thread-0,isAlive:true  
Thread-0,end:false

3：sleep（）当前线程(正在执行的线程)指定的毫秒数内暂停执行

public class threadTest {
    	public static void main(String[] args) throws InterruptedException {
    		System.out.println("begin........");
    		Runnable myRunnable  =new MyRunnable();
    		Thread thread = new Thread(myRunnable);
    		System.out.println(Thread.currentThread().getName());
    		thread.start();
    		Thread.currentThread().sleep(1000);
    		System.out.println("end........");
    	}
    }

public class MyRunnable  implements Runnable{
    	@Override
    	public void run() {
    		System.out.println("Runnable:"+Thread.currentThread().getName());
    	}
    }

运行结果   
begin........  
main  
Runnable:Thread-0  
end........

4：getId（）线程的唯一标识

public class threadTest {
    	public static void main(String[] args) throws InterruptedException {
    		System.out.println("begin........");
    		Runnable myRunnable  =new MyRunnable();
    		Thread myRunnableThread = new Thread(myRunnable);
    		System.out.println(Thread.currentThread().getName()+":"+Thread.currentThread().getId());
    		myRunnableThread.start();
    		MyThread myThread = new MyThread();
    		myThread.sleep(1000);
    		myThread.run();
    		Thread.currentThread().sleep(1000);
    		System.out.println("end........");
    	}
    }

public class MyThread  extends Thread{
    	@Override
    	public void run() {
    		super.run();
    		System.out.println("MyThread:"+Thread.currentThread().getId());
    	}
    }

public class MyRunnable  implements Runnable{
    	@Override
    	public void run() {
    		System.out.println("Runnable:"+Thread.currentThread().getId());
    	}
    }

运行结果   
begin........  
main:1  
Runnable:9  
MyThread:1  
end........  
  
5：yiedld()放弃当前cpu资源，将它让给其他任务去占用cpu执行时间，放弃时间不确定，有可能刚刚放弃马上就获取cpu时间片

public class MyThread  extends Thread{
    	@Override
    	public void run() {
    		long beginTime = System.currentTimeMillis();
    		int count = 0;
    		for(int i=0; i<800000; i++){
    			count = count + (i + 1);
    		}
    		long endTime = System.currentTimeMillis();
    		System.out.println("用时:“"+(endTime-beginTime)+"”,毫秒");
    	}
    }

运行结果：begin........  
用时:“0”,毫秒  
end........

public class MyThread  extends Thread{
    	@Override
    	public void run() {
    		long beginTime = System.currentTimeMillis();
    		int count = 0;
    		for(int i=0; i<800000; i++){
    			Thread.yield();
    			count = count + (i + 1);
    		}
    		long endTime = System.currentTimeMillis();
    		System.out.println("用时:“"+(endTime-beginTime)+"”,毫秒");
    	}
    }

运行结果  
begin........  
用时:“141”,毫秒  
end........  
  
6：停止线程

在java中有3种方式停止正在运行的线程

（1）使用退出标志，使线程正常退出，也就是run方法执行完成后

（2）使用stop（）方法强行终止线程，不推荐

（3）使用interrupt（）方法中断线程，interrupt（）方法仅仅是在当前线程中打了一个停止的标记，并不是真正的停止线程

使用interrupt（）方法中断线程时，先了解如何判断线程状态是否停止，Thread类中提供了两种方法，

（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置清除为false的功能。

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

运行结果  
begin........  
用时:“157”,毫秒  
myThread:false  
myThread:false  
end........

例2

public class threadTest {
    	public static void main(String[] args) throws InterruptedException {
    		System.out.println("begin........");
    		MyThread myThread = new MyThread();
    		myThread.start();
    		//Thread.sleep(1000);
    		Thread.currentThread().interrupt();
    		System.out.println("main:"+Thread.currentThread().interrupted());
    		System.out.println("main:"+Thread.currentThread().interrupted());
    		System.out.println("end........");
    	}
    }
    public class MyThread  extends Thread{
    	@Override
    	public void run() {
    		long beginTime = System.currentTimeMillis();
    		int count = 0;
    		for(int i=0; i<800000; i++){
    			Thread.yield();
    			count = count + (i + 1);
    		}
    		long endTime = System.currentTimeMillis();
    		Thread.currentThread().interrupt();
    		System.out.println("myThread:"+Thread.currentThread().isInterrupted());
    		System.out.println("myThread:"+Thread.currentThread().isInterrupted());
    		System.out.println("用时:“"+(endTime-beginTime)+"”,毫秒");
    	}
    }

运行结果

begin........  
main:true  
main:false  
end........  
myThread:true  
myThread:true  
用时:“129”,毫秒  
  
  
interrupted()的确判断出当前线程是否停止状态，但是为什么第一个interrupted判断为true第二个interrupted判断为false呢？  
如果连续两次调用该方法，则第二次调用将返回false（在第一次调用已清除了其中断状态之后，且第二次调用检验完中断状态前，当前线程再次中断的情况除外）  
  
  
（1）异常法停止线程：

public class threadTest {
    	public static void main(String[] args) {
    		System.out.println("begin........");
    		try {
    			MyThread myThread = new MyThread();
    			myThread.start();
    			myThread.interrupt();
    			Thread.sleep(5000);
    			Thread.currentThread().interrupt();
    			if(Thread.currentThread().interrupted()){
    				System.out.println("main:已经停止状态");
    				throw new InterruptedException();
    			}
    			System.out.println("main1:"+Thread.currentThread().isInterrupted());
    		} catch (InterruptedException e) {
    			System.out.println("main2:"+Thread.currentThread().isInterrupted());
    			e.printStackTrace();
    		}
    		System.out.println("end........");
    	}
    }
    public class MyThread  extends Thread{
    	@Override
    	public void run() {
    		try {
    			for(int i=0; i<10; i++){
    				if(Thread.currentThread().interrupted()){
    					System.out.println("已经停止状态");
    					throw new InterruptedException();
    				}
    				System.out.println("i="+i);
    			}
    			System.out.println("myThread:"+Thread.currentThread().isInterrupted());
    		} catch (InterruptedException e) {
    			System.out.println("exception");
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    	}
    }

运行结果：   
begin........  
已经停止状态  
exception  
java.lang.InterruptedException  
at com.suicai.util.MyThread.run(MyThread.java:10)  
main:已经停止状态java.lang.InterruptedException  
at com.suicai.util.threadTest.main(threadTest.java:16)  
main2:false  
end........  
  
  
（2）沉睡中停止线程

public class threadTest {
    	public static void main(String[] args) {
    		System.out.println("begin........");
    		try {
    			MyThread myThread = new MyThread();
    			myThread.start();
    			myThread.interrupt();
    			Thread.sleep(5000);
    			Thread.currentThread().interrupt();
    			if(Thread.currentThread().interrupted()){
    				System.out.println("main:已经停止状态");
    				throw new InterruptedException();
    			}
    			System.out.println("main1:"+Thread.currentThread().isInterrupted());
    		} catch (InterruptedException e) {
    			System.out.println("main2:"+Thread.currentThread().isInterrupted());
    			e.printStackTrace();
    		}
    		System.out.println("end........");
    	}
    }
    public class MyThread  extends Thread{
    	@Override
    	public void run() {
    		try {
    			System.out.println("开始.............");
    			Thread.currentThread().sleep(20000);
    			System.out.println("myThread:"+Thread.currentThread().isInterrupted());
    			System.out.println("结束.............");
    		} catch (InterruptedException e) {
    			System.out.println("exception");
    			e.printStackTrace();
    		}
    	}
    }

运行结果  
begin........  
开始.............  
exception  
java.lang.InterruptedException: sleep interrupted  
at java.lang.Thread.sleep(Native Method)  
at com.suicai.util.MyThread.run(MyThread.java:8)  
main:已经停止状态java.lang.InterruptedException  
at com.suicai.util.threadTest.main(threadTest.java:16)  
  
  
  
  
main2:false  
end........  
  
  
（3）使用stop()方法暴力停止线程

public class threadTest {
    	public static void main(String[] args) {
    		System.out.println("begin........");
    		try {
    			MyThread myThread = new MyThread();
    			myThread.start();
    			Thread.sleep(5000);
    			Thread.currentThread().interrupt();
    			myThread.stop();
    			if(Thread.currentThread().interrupted()){
    				System.out.println("main:已经停止状态");
    				throw new InterruptedException();
    			}
    			System.out.println("main1:"+Thread.currentThread().isInterrupted());
    		} catch (InterruptedException e) {
    			System.out.println("main2:"+Thread.currentThread().isInterrupted());
    			e.printStackTrace();
    		}
    		System.out.println("end........");
    	}
    }
    public class MyThread  extends Thread{
    	private int i =0;
    	@Override
    	public void run() {
    		try {
    			while (true) {
    				i++;
    				System.out.println("i="+i);
    				Thread.sleep(10000);
    			}
    		} catch (InterruptedException e) {
    			System.out.println("exception");
    			e.printStackTrace();
    		}
    	}
    }

运行结果  
begin........  
i=1  
main:已经停止状态  
main2:false  
java.lang.InterruptedException  
end........  
at com.suicai.util.threadTest.main(threadTest.java:16)