Stack: Peek

Task: Read the top value without removing it

class Stack {    private Object[] a = new Object[N];    private int top = -1;        // -1 means empty     void push(Object v) { a[++top] = v; }    Object pop()        { return a[top--]; }    Object peek()       { return a[top]; }    int size()          { return top + 1; }}

What you are watching

Peek returns the value on top and leaves the stack exactly as it was. It is the operation that separates looking from taking: after a peek the stack still holds three values and the top pointer has not moved. Only the top value can be read this way - there is no operation that reaches past it to B or A.