Here is an example that implements a Stack class based on arrays.

public class Stack {

      private int top;

      private int[] storage;



      Stack(int capacity) {

            if (capacity <= 0)

                  throw new IllegalArgumentException(

                             "Stack's capacity must be positive");

            storage = new int[capacity];

            top = -1;

      }



      void push(int value) {

            if (top == storage.length)

                  throw new StackException("Stack's underlying storage is overflow");

            top++;

            storage[top] = value;

      }



      int peek() {

            if (top == -1)

                  throw new StackException("Stack is empty");

            return storage[top];

      }



      void pop() {

            if (top == -1)

                  throw new StackException("Stack is empty");

            top--;

      }



      boolean isEmpty() {

            return (top == -1);

      }



      public class StackException extends RuntimeException {

            public StackException(String message) {

                  super(message);

            }

      }

}