Recursion - Data Structures and Abstractions with Java - page 163

Once the base case is reached, the suspended executions resume, beginning with the most recent.
Thus, sumOf(2) returns 1 + 2, or 3; then sumOf(3) returns 3 + 3, or 6. Figure 7-5 illustrates this
computation.

Question 4 Write a recursive valued method that computes the product of the integers
from 1 to n , where n > 0.

Note: Should you trace a recursive method?
We have shown you how to trace the execution of a recursive method primarily to show you how
recursion works and to give you some insight into how a typical compiler implements recursion.
Should you ever trace a recursive method? Usually no. You certainly should not trace a recursive
method while you are writing it. If the method is incomplete, your trace will be, too, and you are
likely to become confused. If a recursive method does not work, follow the suggestions given in
the next programming tip. You should trace a recursive method only as a last resort.

FIGURE 7-5

Tracing the execution of sumOf(3)

(a) (b) (c)

sumOf(1):
return 1;

sumOf(2):
return sumOf(1) + 2;

sumOf(2):
return sumOf(1) + 2;

sumOf(3):
return sumOf(2) + 3;

sumOf(3):
return sumOf(2) + 3;

sumOf(3):
return sumOf(2) + 3;

(d) (e) (f)

6 is displayed

sumOf(2):
return 1 + 2 = 3;

sumOf(3):
return 3 + 3 = 6;

sumOf(3):
return sumOf(2) + 3;