This is a discussion of the code we covered in class. I wanted to explain it in terms of the address of the variables, but I found this to be difficult in java. I could have explained it in C++, but there is no sense confusing you with unnecessary information.

I think part of the confusion in class was that we use the same variable name in the function. I have an annotated version of the program listed here, it should explain what is happening. I have links to the actual working code at the bottom of this page.

import java.io.*;
/**
 *Example of reference call
 *

 *  This shows a (possibly) unexpected return from a function.
 *
 *@author Kenneth L Moore
 *@version May 31, 2002
 *
 */
public class Ref{
	
   private final static BufferedReader  stdIn = new  BufferedReader(new  InputStreamReader(System.in));
   private final static PrintWriter  stdOut = new  PrintWriter(System.out, true);
   private final static PrintWriter  stdErr = new  PrintWriter(System.err, true);
	
   private static void  main(String[]  args) throws IOException, NumberFormatException  {
		
      int  x = 5;

      // create an instance of a point initialized to 5,5
      Point  p = new  Point(5, 5);
		
      // call the function
      f(p, x);

      // print out the state of the variables after the function call
      stdOut.println("p is (" + p.getX() + ", " +p.getY() + "), x is " + x);
   }
	
   private static void  f(Point  notTheSame_p, int  notTheSame_x)  {
		
      // here we have a variable (notTheSame_p) that contains a reference to p

       // since here notTheSame_p is referencing the instance created in main
       // we can change values of the instance created in main.
      notTheSame_p.setX(10);
       notTheSame_p.setY(10);

      // this is a copy of x and assigment is to a local variable
      notTheSame_x = 10;

      // within the scope of this function we change what the variable is referencing
      // this has NO effect on the variable p in main.
      notTheSame_p = new  Point(20, 20);

      // the variables (notTheSame_p and notTheSame_x) go out of scope (existance) here
      // we now have nothing referencing the new instance of Point
      // the localy created Point(20,20) will be cleaned up by garbage collection.
   }

}