How do you implement stack in java

Problem statement:
Stack data structure implementation in java.

1. public class Stack {
2.     static final int max = 15;
3.     int top;
4.     int a[] = new int[max];
5.     boolean push(int x) {
6.         if (top >= (max - 1)) {
7.             System.out.println("stack overflow");
8.             return false;
9.         } else {
10.             a[++top] = x;
11.             System.out.println(x + " pushed into stack");
12.             return true;
13.         }
14.     }
15.     int pop() {
16.         if (top < 0) {
17.             System.out.println("stack underflow");
18.             return 0;
19.         } else {
20. 
    
21.             int x = a[top--];
22.             return x;
23.         }
24.     }
25.     int size() {
26.         return top + 1;
27.     }
28.     boolean isEmpty() {
29.         return top == -1;
30.     }
31.     boolean isFull() {
32.         return (top == (max - 1));
33.     }
34.     int peak() {
35.         if (!isEmpty())
36.             return a[top];
37.         else return -1;
38.     }
39.     Stack() {
40.         top = -1;
41.     }
42. }
43. class MainExecution {
44.     public static void main(String[] args) {
45.         Stack s = new Stack();
46.         s.push(10);
47.         s.push(20);
48.         s.push(30);
49.         System.out.println("size: " + s.size());
50.         s.push(25);
51.         System.out.println("new size: " + s.size());
52.         System.out.println(s.pop() + " popped from stack");
53.         System.out.println("top element is peak: "+s.peak());
54.     }
55. }

Output:

10 pushed into stack

20 pushed into stack

30 pushed into stack

size: 3

25 pushed into stack

new size: 4

25 popped from stack

top element peak: 30