To check for any loop existence in the Linked List

is-Loop-in-List.java

package datastructures;

import java.util.ArrayList;

public class checkLoop {
    Node head = null;
    Node last = null;
    int size = 0;
    
    static class Node {
        int data = 0;
        Node next = null;
        
        Node(int val) {
            data = val;
            next = null;
        }
    }
    
    private void insert(int val) {
        Node newNode = new Node(val);
        
        if(head == null) {
            head = newNode;
            last = newNode;
        } else {            
            last.next = newNode;
            last = newNode;
        }
        size++;
    }
    
    private Boolean checkForLoop() {
        Node trav = head;
        ArrayList<Node> arr = new ArrayList<>();
        
        int flag = 0;
        int counter = 0;
        while(trav != null) {
            arr.add(trav);
            counter++;
            int inCounter = 0;
            for(Object i : arr) {
                if(inCounter < counter-1) {
                    if(trav == (Node) i) {
                        flag = 1;
                        break;
                    }
                }                
                inCounter++;
            }
            trav = trav.next;
            if(flag == 1)
                break;
        }
        arr.clear();
        return flag == 1;
        
    }
    
    private void display() {
        Node trav = head;
        if(checkForLoop()) {
            System.out.println("List is Modified!!, Loop exists");
            return;
        }
        do {
            System.out.println(trav.data+ " " + trav.next);
            trav = trav.next;
        } while(trav != null);
    }
    
    private void changeTheData() {
        // changes the last Node next to somewhere inside the list to form a Loop
        last.next = head.next.next.next.next;
    }
    
    public static void main(String[] args) {
        checkLoop cL = new checkLoop();
        
        cL.insert(1);
        cL.insert(2);
        cL.insert(3);
        cL.insert(4);
        cL.insert(5);
        cL.insert(6);
        cL.insert(7);
        
        cL.display();
        
        cL.changeTheData();
        
        cL.display();
    }
}