Stack

[Arpana Rai]

 
import java.util.Stack; 
public class aClass 
{ 
public static void main(String []agrs) 
{ 
Stack st1 = new Stack(); 
Stack st2 = new Stack(); 
new aClass().Method(st1, st2); 
System.out.println("st1 has: " + st1); 
System.out.println("st2 has: " + st2); 
} 
private void Method(Stack st1,Stack st2) 
{ 
st2.push(new Integer(100)); 
st1 = st2; 
} 
} 
 

The output of above code is:
st1 has: []
st2 has: [100]
I thought the output would be:
st1 has: [100]
st2 has: [100]


Plz some one explain me why the above code gives such output??
regds
Arpana

[Jose Botella]

Inside method, the parameters st1 and st2 are not the same as the local variables st1 and st2 in the main method. Think of them as st1' and st2' . After the invokation they point to the same Stack objects as the local variables in main do. Therefore, modifying the content of st2' will also be reflected in the variable st2 in the main method. However st1'= st2' will not set st1 to st2' , because st1 and st1' are different variables. st1' dissapears after the method invokation returns, but st1 remains unchanged.