Fundamentals - SCJP Sun Certified Programmer for Java Platform SE6 - page 40

objects. Three strings are pushed onto the names stack, and two ints are pushed onto
grades . Then names and grades are passed into modifyStacks . The parameter one points
to the stack of Strings and two points to the stack of grades , as Figure 1.13 shows.

FIGURE 1.13 The references from main are copied into the parameters of
modifyStacks .

“Jane”
“Edward”
“Kim”

names one

grades two

87
95

The memory of the
call stack for main

Heap The memory of the

call stack for modifyStacks

Pushing 50 onto two is the same as pushing it onto grades because the two references
point to the same stack. Similarly, popping a value off one removes “Jane” from the names
stack.
Note that setting one equal to a new Stack does not affect the Stack that names points
to. We cannot modify the reference names within modifyStacks . Figure 1.14 shows the
references and objects just before the modifyStacks method returns.

FIGURE 1.14 Assigning the one reference to a new Stack does not affect the names
stack.

names one

“Edward”
“Kim”

grades two

50

87
95

The memory of the
call stack for main

Heap The memory of the

call stack for modifyStacks