sciuriware
asked on
Runtime.addShutDownHook() prefers Thread above Runnable
///////////I was puzzled when my code was refused by the compiler:
public class X implements Runnable
{
public void run() { ..... } // What ever when it dies.
private X(){} // Don't create objects.
public static void action() // One of the methods, not instantiating this class.
{
Runtime.getRuntime().addSh
}
}
///////Things got better with :
public class X extends Thread
....
//////I should understand this but the coin won't drop this morning.
public class X implements Runnable
{
public void run() { ..... } // What ever when it dies.
private X(){} // Don't create objects.
public static void action() // One of the methods, not instantiating this class.
{
Runtime.getRuntime().addSh
}
}
///////Things got better with :
public class X extends Thread
....
//////I should understand this but the coin won't drop this morning.
girionis
What's the error message?
ASKER
Cut from the ECLIPSE error window:
Error
The method addShutdownHook(Thread) in the type Runtime is not applicable for the arguments (X) X.java GoiDo/RiengTu line 125
Don't be confused by the package name.
;JOOP!
Error
The method addShutdownHook(Thread) in the type Runtime is not applicable for the arguments (X) X.java GoiDo/RiengTu line 125
Don't be confused by the package name.
;JOOP!
It seems that addShutdownHook requires a Thread as a parameter. It must need some of the facilities provided by a Thread, otherwise the parameter would be a Runnable (as you originally tried).
The method can't down-cast your Runnable to a Thread.
The method can't down-cast your Runnable to a Thread.
Weird... Can you try and cast X to Thread?
ASKER
No, can't cast.
;JOOP!
;JOOP!
If all else fails use an inner thread class.
Can't you do:
Runnable x = new X();
Thread t = (Thread) x;
Runtime.getRuntime().addSh
Runnable x = new X();
Thread t = (Thread) x;
Runtime.getRuntime().addSh
Ehm.. sorry I meant:
Runnable x = new X();
Runtime.getRuntime().addSh
Runnable x = new X();
Runtime.getRuntime().addSh
ASKER
No girionis, you can't cast a Runnable to a Thread.
Did you check your advises in advance?
;JOOP!
Did you check your advises in advance?
;JOOP!
I didn't actually. I thought the compiler would accept it (I should go back to reading simple OO concepts I guess :( )... anyway just use an inner Thread class:
Runtime.getRuntime().addSh
Runtime.getRuntime().addSh
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
As I prefer to extend my classes or to implement on them (access to variables) I accept that I must extend from Thread.
Although the answer did not explain everything I guess jimmack kept to the rules and facts of JAVA. And 50 points is not much in these days ....
;JOOP!
Although the answer did not explain everything I guess jimmack kept to the rules and facts of JAVA. And 50 points is not much in these days ....
;JOOP!
;-)
Thanx.
Thanx.
Actually this:
>Runnable x = new X();
>Runtime.getRuntime().addS
*compiles perfectly* even though it throws a run-time error. ;-)
>Runnable x = new X();
>Runtime.getRuntime().addS
*compiles perfectly* even though it throws a run-time error. ;-)
That's because the compiler assumes (in this case, falsely ;-)) that if you're forcing a cast, you know what you're doing ;-)
ASKER
Thank you girionis, although you can't make me happy with runtime errors .......
;JOOP!
;JOOP!
jimmack true, I just thought sciuriware meant a compile-time error.