Simple Java Implementation of Stack

ArrayStackJava.java

// www.abukhleif.com
class ArrayStack {
  private final int[] stack;
  private final int size;
  private int top;

  public ArrayStack(int size) {
    this.size = size;
    stack = new int[size];
  }

  boolean isEmpty() { // check if the stack is empty
    return top == 0;
  }

  boolean isFull() { // check if the stack is full
    return top == size;
  }

  void push(int x) { // add an item to the top of the stack
    if (!isFull()) {
      stack[top++] = x;
    } else {
      throw new RuntimeException("The stack is full");
    }
  }

  int pop() { // get the top item of the stack, then remove it
    if (!isEmpty()) {
      return stack[--top];
    } else {
      throw new RuntimeException("The stack is empty");
    }
  }
  
  int top() { // get the top item of the stack
    if (!isEmpty()) {
      return stack[top];
    } else {
      throw new RuntimeException("The stack is empty");
    }
  }
}