Object-Oriented Design - Java Software Solutions: Foundations of Program Design - page 342

the method returned, that formal parameter was destroyed and the Num object it
referred to was marked for garbage collection. The only change that is “perma-
nent” is the change made to the state of the second parameter. Figure 7.5 shows
the step-by-step processing of this program.

STEP 1 STEP 2

Before invoking changeValues tester.changeValues (a1, a2, a3);

a1 a2 a3 a1 a2 a3

111 222 333 111 222 333

f1 f2 f3 f1 f2 f3

111

STEP 3 STEP 4

f1 = 999; f2.setValue (888);

a1 a2 a3 a1 a2 a3

111 222 333 111 888 333

f1 f2 f3 f1 f2 f3

999 999

STEP 5 STEP 6

f3 = new Num (777);

After returning from changeValues

a1 a2 a3 a1 a2 a3

111 888 333 111 888 333

f1 f2 f3 f1 f2 f3

999 777

= Undefined

FIGURE 7.5 Tracing the parameters in the ParameterTesting program