Answers to Self-Study Questions

Test Yourself #1

When the program executes, this is printed: 

  10
  Ann
This is because the assignment P.age = 10 in method changePerson modifies the age field of the object in the heap pointed to by its Person parameter, which is the same object pointed to by variable P in main.

However, the modification to the name field has no effect on the Person pointed to by main's P, because when that statement is executed, formal parameter P has already been set to point to a different Person object.

Test Yourself #2

Here are pictures assuming that parameters are passed by value. Only the space for parameters and local variables is shown for the ARs.

Stack when swap is first called: 

       +====+
    y: | 20 |
       +----+
    x: | 10 |
       +====+        +-------------------+
    A: |  ---------> | 10 | 20 | 30 | 40 |
       +====+        +-------------------+
Stack just before swap returns: 
       +====+
    y: | 10 |
       +----+
    x: | 20 |
       +====+        +-------------------+
    A: |  ---------> | 10 | 20 | 30 | 40 |
       +====+        +-------------------+
Here are pictures assuming that parameters are passed by reference. Only the space for parameters and local variables is shown for the ARs.

Stack when swap is first called: 

       +====+
    y: | -------------------+
       +----+               |
    x: | --------------+    |
       +====+          v    v
    A: |  ---------> +-------------------+
       +====+        | 10 | 20 | 30 | 40 |
		     +-------------------+
Stack just before swap returns: 
       +====+
    y: | -------------------+
       +----+               |
    x: | --------------+    |
       +====+          v    v
    A: |  ---------> +-------------------+
       +====+        | 20 | 10 | 30 | 40 |
		     +-------------------+