ArrayStack.java

public class ArrayStack {

 private static final int MAX = 100;
 private int top;
 private int[] stack = new int[MAX];

 public ArrayStack() {
 this.top = -1;
 }

 public int push(int n) {
 if (top >= (MAX - 1)) {
 return -1; // stack overflow
 } else {
 stack[++top] = n; // updating top position & pushing onto stack
 return n;
 }
 }

 public int pop() {
 if (!isEmpty()) {
 return stack[top--];
 } else return -1; // stack underflow
 }

 public int peek() {
 if (!isEmpty()) 
 return stack[top];
 else return -1; // stack underflow
 }
 
 public boolean isEmpty() {
 return top == -1;
 }

}