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Message:

Passing objects to a method.

Posted by Igor on July 30, 2001 at 9:13 AM

Hello!
In Java all object pass to a method by reference. I have got th problem writing 'swap' method:

/// Code start
class Simple {
public int value;
}

class Swap {
public void swap(Simple obj1, Simple obj2) {
Simple temp = new Simple();

System.out.println(" Inside swap method.");
System.out.println(" obj1.value = " + obj1.value);
System.out.println(" obj2.value = " + obj2.value);

temp = obj1;
obj1 = obj2;
obj2 = temp;

System.out.println("obj1.value = " + obj1.value);
System.out.println("obj2.value = " + obj2.value);
}

public static void main(String [] args) {
Simple obj1 = new Simple();
Simple obj2 = new Simple();

obj1.value = 10;
obj2.value = 25;

System.out.println("Inside main method.");
System.out.println("obj1.value = " + obj1.value);
System.out.println("obj2.value = " + obj2.value);

swap(obj1, obj2);

System.out.println("After swap method.");
System.out.println("obj1.value = " + obj1.value);
System.out.println("obj2.value = " + obj2.value);
}
}
/// Code end

The program output was very surprised:

Inside main method.
obj1.value = 10
obj2.value = 25
Inside swap method.
obj1.value = 10
obj2.value = 25
obj1.value = 25
obj2.value = 10
After swap method.
obj1.value = 10
obj2.value = 25

If all object pass to a method by refference than after swap method its values should be changed... I don't understand why its didn't.
Could somebode explain me where is error?

Thank you.

I am sorry for a big message.

• Passing objects to a method. Dmitry July 30, 2001 at 1:54 PM (1)
  • Thank you, it is clear. Igor July 31, 2001 at 7:59 AM (0)