Doubt in thread

[Frederico Benevides]

I don't know why it works, because I thought in "laurel.wait(1000);" the wait has to be inside in a synchronized block or synchronized method, but I don't understand why in here is not in this and it works.

Thank you.

public class TwoThreads {

static Thread laurel, hardy;

public static void main(String[] args) {

laurel = new Thread() {
public void run() {
System.out.println("A");
try {
hardy.sleep(1000);
}
catch(Exception e) {
System.out.println("B");
}
System.out.println("C");
}
};

hardy = new Thread() {
public void run() {
System.out.println("D");
try {
laurel.wait(1000);
}
catch(Exception e) {
System.out.println("E");
}
System.out.println("F");
}
};

laurel.start();
hardy.start();
}
 
}
 

And here, the wait has the problem because is not inside in a synchronized block.

public class Test {
 
public static synchronized void main(String[] args) throws
 InterruptedException {

    Thread t = new Thread();
    t.start();
    System.out.print("X");
//    t.wait(10000);
    System.out.print("Y");
    
    String s = "teste";
    
    s.wait(199);
}
 
}
 

[ March 08, 2006: Message edited by: Frederico Benevides ]

[Keith Lynn]

In the first program, you are calling the wait method from within a try block which has a corresponding catch block that ignores all checked exceptions. If you add a print statement in the catch block to print out the name of the exception, this is one possible output.

A
D
java.lang.IllegalMonitorStateException: current thread not owner
E
F
C
 

In the second program you are not catching and ignoring any checked exception so you get the IllegalMonitorStateException.
[ March 08, 2006: Message edited by: Keith Lynn ]

[Frederico Benevides]

Wow, is true, how I didn't see that

thank you!

[Stephen O'Kane]

I have a question about this code example (TwoThreads class). It comes from K&B's book, page 756.

Given the above code which letters will eventually appear somewhere in the output? (choose all that apply.)

A. A
B. B
C. C
D. D
E. E
F. F
G. The answer cannot be reliably determined
H. The code does not compile


the answer is:

A, C, D, E, F.

I don't understand why B is not a correct answer, as is it not possible that a InterruptedException (or any other random exception) occurs, therefore B might be printed? Or are these sort of things ignored in the exam. I thought the answer would be G, as it cannot be relibly determined if B will be output or not.

Plus, the book says that on the exam, the number of options for an answer will be given. In this case, does this mean that in the exam they will tell us 5 answers are correct? That would make this question infinitely more obvious.

Thanks for your time
Sok