Collections

public class Stack {

    private int[] arr;
    private int top;
    private int capacity;

    public Stack(int size) {
        arr = new int[size];
        capacity = size;
        top = -1;
    }

    public void push(int x) {
        if (isFull()) {
            System.out.println("Stack is full.");
            return;
        }
        arr[++top] = x;
    }

    public int pop() {
        if (isEmpty()) {
            System.out.println("Stack is empty.");
            return -1;
        }
        return arr[top--];
    }

    public int peek() {
        if (isEmpty()) {
            System.out.println("Stack is empty.");
            return -1;
        }
        return arr[top];
    }

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

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

    public static void main(String[] args) {
        Stack stack = new Stack(5);
        stack.push(1);
        stack.push(2);
        stack.push(3);
        stack.push(4);
        stack.push(5);
        stack.push(6);
        System.out.println("Peek: " + stack.peek());
        System.out.println("Pop: " + stack.pop());
        System.out.println("Pop: " + stack.pop());
        System.out.println("Peek: " + stack.peek());
        
    }
}
Stack.main(null);

Stack is full.
Peek: 5
Pop: 5
Pop: 4
Peek: 3