package Stack_Java;

public class ArrayStack { 
      private int top; 
      private int capacity = 100;
      private Object[] storage; 
 
      ArrayStack() { 
            storage = new Object[capacity]; 
            top = -1; 
      } 
 
      void push(Object value) { 
            if (top == storage.length) 
                  throw new StackException("Stack's underlying storage is overflow"); 
            top++;
            storage[top] = value; 
      } 
 
      Object peek() { 
            if (top == -1) 
                  throw new StackException("Stack is empty"); 
            return storage[top]; 
      } 
 
      Object pop() { 
            if (top == -1) 
                  throw new StackException("Stack is empty"); 
            Object result = storage[top--];
            return result;
      } 
 
      boolean empty() { 
            return (top == -1); 
      } 
  
      public class StackException extends RuntimeException { 
            public StackException(String message) { 
                  super(message); 
            } 
      } 
}