Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

we indicate that the stack no longer needs to hold a reference to object e. Indeed,
if there are no other active references to e, then the memory space taken by e will
be reclaimed by the garbage collector.
Table 5.1 shows the running times for methods in a realization of a stack by an
array. Each of the stack methods in the array realization executes a constant
number of statements involving arithmetic operations, comparisons, and
assignments. In addition, pop also calls isEmpty, which itself runs in constant
time. Thus, in this implementation of the Stack ADT, each method runs in
constant time, that is, they each run in O(1) time.
Table 5.1: Performance of a stack realized by an
array. The space usage is O(N), where N is the size of
the array, determined at the time the stack is
instantiated. Note that the space usage is independent
from the number n ≤ N of elements that are actually
in the stack.
Method
Time
size
O(1)
is Empty
O(1)
top
O(1)
push
O(1)
pop
O(1)
A concrete Java implementation of the pseudo-code of Code Fragment 5.3, with
Java class ArrayStack implementing the Stack interface, is given in Code
Fragments 5.4 and 5.5. Unfortunately, due to space considerations, we omit most
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