Doubts

[Malli Raman]

Hi All,
Sorry for asking this in this forum. I have some basic doubts in Java
1. class a
{
public synchronized void foo() {}
public synchronized void foo1(){}
public void foo2()
}
In this class whether can I able to call foo() & foo1() & foo2() method at the same time.
Answer: Actually my answer is that it is not possible to call method at the same time as the object is locked by the monitor.
2. class A
{
public void foo() throws Exception{}
}
class B
{
public void foo(){}
}

In both cases whether both methods are overrided or overloaded?

My Answer is it is a overrided method as it will consider only the method signature mainly the no of arguments and the type of arguement.
Regards,
M.S.Raman

[Bear Bibeault]

Sorry for asking this in this forum. I have some basic doubts in Java

If you know that this is not the appropriate forum for the question, why didn't you just ask it in the right one?

[Jim Yingst]

Since this has nothing at all to do with servlets, I'm moving this thread to Java in General - Intermediate.

[Ernest Friedman-Hill]

In both cases whether both methods are overrided or overloaded?

Since the classes A and B are unrelated in your example, the two "foo" methods aren't an example of either overriding or overloading. They're just two methods with the same name. Did you mean to make one class extend the other? If B extends A, then this is fine; B's foo() overrides A's foo. But if A extends B, it'd be a compile-time error, as the methods would still override eachother (as their argument lists are the same) but the child's exception signature is less restrictive than the parent's, which is not allowed.

[Malli Raman]

Hi,
Thanks for replying. Yes, I missed the extends keyword. It is class B extends class A. In this case your saying the method in B is overrided the method in A. Am I right. Do you have any idea about the first question.
Regards,
M.S.Raman

Originally posted by Ernest Friedman-Hill:

Since the classes A and B are unrelated in your example, the two "foo" methods aren't an example of either overriding or overloading. They're just two methods with the same name. Did you mean to make one class extend the other? If B extends A, then this is fine; B's foo() overrides A's foo. But if A extends B, it'd be a compile-time error, as the methods would still override eachother (as their argument lists are the same) but the child's exception signature is less restrictive than the parent's, which is not allowed.

[Ernest Friedman-Hill]

Yes, B.foo() overrides A.foo() in that case. And your understanding of the synchronized methods in the first question is correct.

[Azriel Abramovich]

Java is aware that it might be necessary to pass from one synced method to another, thus it allows it. It allows the propagation of the calls as long as the same monitor is caught.
In your question the class monitor is caught and thus both methods will allow propagation of calls between them by the holder of the monitor.
consider the following example:

  
public class Zevel{
  Object lock1 = new Object();
  Object lock2 = new Object();
}

[Azriel Abramovich]

sorry, hit the TAB key and then pressed space.... this is to continue:
consider the following example:

  
public class Zevel{
  Object lock1 = new Object();
  Object lock2 = new Object();
  public void a(){
     synchronized(lock1){
         .....
     }
  }
  public void b(){
     synchronized(lock2){
         .....
     }
  }
}

Even in this case, propagation of calls from a() to b() will be possible (within the synced blox) because they have the same monitor owner.
In your example and in mine if two different monitor owners (threads) would try to 'use' the same synched area of code the synch mechanism would get to work and block one thread until the other is done.
Hope this helped.
This was made this way to avoid dead-locks.

[Malli Raman]

Thanks Ernest Friedman-Hill & Azriel Abramovich for replying my query. Is there any way i can test this.
I tried this by running two seperate threads for printing 10000 numbers, but i am not able to differentiate it. Please help me to sort out this issue.
public class Zevel
{
Object lock1 = new Object();
Object lock2 = new Object();
int i;

public void a()
{ synchronized(lock1)
{
i++;
System.out.println("Inside a");
System.out.println(i);
}
}

public void b()
{ synchronized(lock2)
{
System.out.println("Inside b");
}
}

public static void main(String args[])
{
Zevel z= new Zevel();
for (int i= 0;i<10000;i++)
z.a();
z.b();
}
}
Regards,
M.S.Raman

Originally posted by Azriel Abramovich:
sorry, hit the TAB key and then pressed space.... this is to continue:
consider the following example:

  
public class Zevel{
  Object lock1 = new Object();
  Object lock2 = new Object();
  public void a(){
     synchronized(lock1){
         .....
     }
  }
  public void b(){
     synchronized(lock2){
         .....
     }
  }
}

Even in this case, propagation of calls from a() to b() will be possible (within the synced blox) because they have the same monitor owner.
In your example and in mine if two different monitor owners (threads) would try to 'use' the same synched area of code the synch mechanism would get to work and block one thread until the other is done.
Hope this helped.
This was made this way to avoid dead-locks.