Stack Data Structure in Java | push, put -> 0(1)

CustomStack.java

public class CustomStack {

    private int size;
    private final int[] arr;

    public CustomStack(int maxSize) {
        this.arr = new int[maxSize];
        this.size = -1;
    }

    public void push(int x) {
        if (!isFull()) {
            arr[++size] = x;
        }
    }

    public int pop() {
        if (!isEmpty()) {
            return arr[size--];
        }

        return -1;
    }

    public void increment(int k, int val) {
        if (!isEmpty()) {
            for (int i = 0; i < k && i <= size; i++) {
                arr[i] += val;
            }
        }
    }

    private boolean isEmpty() {
        return size == -1;
    }

    private boolean isFull() {
        return size == arr.length - 1;
    }
}