Implementing Stacks: Array

Another method we could explore for implementing a stack would be the array implementation, the decision between linked lists and arrays will be an important discussion point to consider when looking at requirements.

Array Implementation of a Stack

• Use array s[] to store N items on a stack
• push(): add new item at s[N]
• pop(): remove item from s[N-1]

s[]

to	be	or	not	to	be	null	null	null	null
0	1	2	3	4	5	6	7	8	9
Defect : Stack overflows when N exceeds capacity - Stack has a certain capacity that needs to be declared ahead of time. This is a fundamental problem of arrays.

Full Implementation using Array

public class FixedCapacityStackOfStrings{
  private String[] s;
  private int N = 0;

  public FixedCapacityOfStrings(in capacity)
  { s = new String[capacity]; }

  public boolean isEmpty()
  { return N == 0; }

  public void push(String item)
  { s[N++] = item; }

  public void pop()
  { return s[--N]; }
}