Java - Finding Duplicates in Array and printing them only Once

I am trying to loop through my array and find all the numbers that are repeating more than once:

E.G: if there is 1 1 2 3 4

It should print saying "1 repeats more than once"

Here is my code and so far what I have tried, however it prints all duplicates and keep going, if there is 4 4 4 4 3 6 5 6 9, it will print all the 4's but i dont want that:

class average {

 public static void main(String[] args) throws IOException {

    int numOfLines = 0;
    int sum = 0, mean = 0, median = 0, lq = 0, uq = 0;
    int[] buffer;

    File myFile = new File("num.txt");
    Scanner Scan = new Scanner(myFile);

    while(Scan.hasNextLine()) {
        Scan.nextLine();
        numOfLines++;
    }
    Scan.close();
    Scan = new Scanner(myFile);

    System.out.println("Number Of Lines: " + numOfLines);

    buffer = new int[numOfLines];

    for(int i=0; i<numOfLines; i++) {
        buffer[i] = Scan.nextInt();
    }
    Scan.close();
    Scan = new Scanner(myFile);

    for(int i=0; i<buffer.length; i++) {
        sum = sum+i;
        mean = sum/numOfLines;
    }
    System.out.println("Sum: " + sum);
    System.out.println("Mean: " + mean);

    for(int i=0; i<buffer.length; i++) {
        for(int k=i+1; k<buffer.length; k++) {
            if(buffer[k] == buffer[i]) {
                System.out.println(buffer[k]);
            }
        }
    }