Find duplicate elements in array in O(N) time

FindDuplicates.java

/*  Find if given array has duplicate elements (more than 1 occurence)
    Time Constraint: O(N)
    Author: Jayesh CP
*/

import java.util.*;
import java.lang.*;
import java.io.*;

public class FindDuplicates
{
    public static void main (String[] args) throws java.lang.Exception
    {
        
        int[] nums = {1,2,3,4,5,5,6,7,8,8,9,1};
                
        if(hasDuplicates(nums)) {
            System.out.println("Found duplicates !");
        } else {
            System.out.println("No duplicates");
        }

    }

    private static void hasDuplicates(int[] nums) {

        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        boolean duplicate = false;
        
        for(int i = 0; i < nums.length; i++) {
            if(map.containsKey(nums[i])) {
                map.put(nums[i], (map.get(nums[i]) + 1));
                duplicate = true;
                break;
            } else {
                map.put(nums[i], 1);
            }
        }
        // printDuplicates(map);
        return duplicate;

    }
    
    /*
    private static void printDuplicates(Map<Integer, Integer> map) {

        Iterator it = map.entrySet().iterator();
        while(it.hasNext()) {

            Map.Entry pairs = (Map.Entry)it.next();
            if((int)pairs.getValue() > 1) {
                System.out.print(pairs.getKey() + " ");
            }

        }

    }
    */
}