Create a stack structure in Java

//w  w w  . ja v a2 s  .  c om
class Stack {
  private int maxSize;

  private double[] stackArray;

  private int top;

  public Stack(int s) {
    maxSize = s;
    stackArray = new double[maxSize];
    top = -1; 
  }

  public void push(double j) {
    stackArray[++top] = j;
  }

  public double pop() {
    return stackArray[top--];
  }

  public double peek() {
    return stackArray[top];
  }

  public boolean isEmpty() {
    return (top == -1);
  }

  public boolean isFull() {
    return (top == maxSize - 1);
  }
}

public class Main {
  public static void main(String[] args) {
    Stack theStack = new Stack(10);
    theStack.push(20);
    theStack.push(40);
    theStack.push(60);
    theStack.push(80);

    while (!theStack.isEmpty()) {
      double value = theStack.pop();
      System.out.print(value);
      System.out.print(" ");
    }
    System.out.println("");
  }
}