When the program executes, this is printed:
10 AnnThis 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.
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 |
+-------------------+
Test Yourself #3: One way the caller can implement it is as follows.
la $t0 _x # Load address of _x into T0 sw $t0 0($sp) subu $sp $sp 4 # Move stack pointer lw $t0 _y # Load value of _y into T0 sw $t0 0($sp)subu $sp $sp 4 # Move stack pointer