correct argument to put in synchronized method

[markthien]

Hi guys,

I am wondering what is the proper argument to pass in a synchronized method:

public void method1() { 
    synchronized( this ) { 
        ....
    }
}

public void method1() { 
    synchronized( MyClass.class) { 
        ....
    }
}

public void method1() { 
    synchronized( MyClass.class) { 
        ....
    }
}

public void method1() { 
    A objecta=new A();
    synchronized( objecta) { 
        ....
    }
}

Please kindly advice. Thanks in advance!

Cheers,
Mark Thien

[eRaaaa]

We cannot tell you which one is right. It depends on what do you want to do :)

Intrinsic Locks and Synchronization (The Java™ Tutorials > Essential Classes > Concurrency)

[Norm]

what is the proper argument to pass in a synchronized method

There is no requirement to pass any arguments to a synchronized method.

[aburnett397]

Synchronized segments in your code can only be executed by a single thread at a time for which the same object was provided as an "argument". Therefore...

public void method1() {
synchronized( this ) {
....
}
}
method1() cannot run simultaneously for a given instance. This is the same as 'public synchronized void method1() {...}'

public void method1() {
synchronized( MyClass.class) {
....
}
}
method1() cannot run simultaneously for any instance

public void method1() {
A objecta=new A();
synchronized( objecta) {
....
}
}
No synchronization since each call to method1() synchronizes on a different object