Java Reference
In-Depth Information
In Chapter 6, the
stack
data structure was introduced in the context of understanding how
Java performs method calls. We discussed both the
method-call stack
and
stack frames
. In
this section, we'll use these concepts to demonstrate how the program-execution stack
handles
recursive
method calls.
Let's begin by returning to the Fibonacci example—specifically, calling method
fibo-
nacci
with the value
3
, as in Fig. 18.6. To show the
order
in which the method calls' stack
frames are placed on the stack, we've lettered the method calls in Fig. 18.7.
A
fibonacci( 3 )
B
fibonacci( 2 )
E
fibonacci( 1 )
C
fibonacci( 1 )
D
fibonacci( 0 )
return 1
return 1
return 0
Fig. 18.7
|
Method calls made within the call
fibonacci(3)
.
When the first method call (
A
) is made, a
stack frame
containing the value of the local
variable
number
(
3
, in this case) is
pushed
onto the
program-execution stack
. This stack,
including the stack frame for method call
A
, is illustrated in part (a) of Fig. 18.8. [
Note:
We use a simplified stack here. An actual program-execution stack and its stack frames
would be more complex than in Fig. 18.8, containing such information as where the
method call is to
return
to when it has completed execution.]
(a)
(b)
(c)
(d)
Top of Stack
Top of Stack
Top of Stack
Method call:
C
number = 1
Method call:
B
number = 2
Method call:
A
number = 3
Method call:
D
number = 0
Method call:
B
number = 2
Method call:
A
number = 3
Top of Stack
Method call:
E
number = 1
Method call:
A
number = 3
Method call:
A
number = 3
Fig. 18.8
|
Method calls on the program-execution stack.
