Quest : Interrupt, isInterrupted, interrupted

[Anonymous]

Hello All,

Please go throught the below code

    
public class SCJPClass implements Runnable{
public void run(){
try
{
System.out.println("In run");
Thread.sleep(10000);
System.out.println("I'm awake");
}
catch(InterruptedException e){
e.printStackTrace();
}
}
public static void main(String[] args)throws Exception{
Thread t=new Thread(new SCJPClass());
t.start();
System.out.println("started");
t.sleep(2000);

System.out.println("Interrupting");  
t.interrupt();  //line #1
System.out.println(t.isInterrupted());//returned false
System.out.println("ended");
}
}
 
Output:
 
started
In run
Interrupting
java.lang.InterruptedException: sleep interrupted
true
ended
at java.lang.Thread.sleep(Native Method)
at SCJPClass.run(SCJPClass.java:6)
at java.lang.Thread.run(Unknown Source)

My question is on line #1 we have interruptd the thread t, which is sleeping for 10secs. Then why does isInterrupted() on t returns false.

from the java API at http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Thread.html#interrupt()

I understood that , if a thread is interrupted it should return true otherwise it should return false. But in our case, we have actually interrupted the thread then why did isInterrupted() return false. Please clarify me on this.

[Fusheng Xiao]

it's because when you try to use sleep() on a slept Thread,fine,A InterruptedException is thrown as the slept Thread's interrupted state being remove ,so it returns false when you use t.isInterrupted();

[ahmed yehia]

So catching the exception caused isInterrupted() to return false?

I have modified the program so that the thread is interrupted while running without using sleep() and catch(). Now the isInterrupted() returns true.
please clarify.

    
public class Interrupt implements Runnable {
static boolean b = true;
public void run(){
for(;b ;)  {}
}
public static void main(String[] args)throws Exception{
Thread t=new Thread(new Interrupt());
t.start();
System.out.println("started");
Thread.sleep(2000);
System.out.println("Interrupting");
t.interrupt();  
System.out.println(t.isInterrupted());//now return true
System.out.println("ended");
b = false;
}
}

output:
started
Interrupting
true
ended
[ September 23, 2007: Message edited by: Ahmed Yehia ]

[Fusheng Xiao]

That is , When you call sleep(); twice on a Thread,the isInterrupted is being removed . but you call interrupt() after sleep().JVM does not automaticely remove the isInterrupted() .so the isInterrupted() return true.
Shortly speaking,isInterrupted() change into true while calling interrupt().but not changed into false while calling interrupt() on a interrupted Thread.
Hoping you can understand . you can check on the API to get more information.