synchronize

[Richard Wilson]

//if a thread defined like this in a class
new Thread() {
public void run(){
synchronized(this) {
System.out.println("Reach Sync");
}
}
}.start();
What does the this refer to?
When a thread goes into the sync block,whose lock
the thread will acquire?Thread Object or Enclosing Class Object?

[Rajinder Yadav]

The "this" operator refers to the object itself, take a looks at this code, and note how "this.i" refers to the object's variable i which is use to distinguish between the passed var i within the ctor!

class Test {
  int i = 10;
  
  Test(int i) {
    this.i = i;
  }
}

A call to synchronized(this) will lock on the object that the call in made from, any other threads that try to aquire a lock on this object will block until the synchronized block completes!
[ February 18, 2002: Message edited by: Rajinder Yadav ]

[Rob Ross]

Originally posted by Richard Wilson:
//if a thread defined like this in a class
new Thread() {
public void run(){
synchronized(this) {
System.out.println("Reach Sync");
}
}
}.start();

This code is equivalent to:

new Thread() {
  public void synchronized run(){
      System.out.println("Reach Sync");
  }
}.start();

[Richard Wilson]

Then you mean that "this " refers to thread object
defined in the anonymous class,right?

[Rob Ross]

Right.
an unqualified this always refers the innermost object in which it is encountered.
You can also qualify the this with the name of an enclosing class, and it will evaluate to that object.
For example:

class Foo {
    int i=5;
    public void aMethod()
    {
        System.out.println(this.i);//prints 5
        Object o = new Object(){
                  int i = 7;
                  public void aMethod(){
                      System.out.println(this.i);//prints 7
                      System.out.println(Foo.this.i); //prints 5
                  }
         }

    }
}//end class Foo

[ February 18, 2002: Message edited by: Rob Ross ]

[Murgan Sub]

public class Foo {
int i=5;
public void aMethod() {
System.out.println(this.i);
Object o = new Object(){
int i = 7;
public void aMethod(){
System.out.println(this.i); System.out.println(Foo.this.i);
}
}; // Semicolon required here
}
}
Just Corrected the syntax