java - Finding Duplicates in Array and printing them only Once -

i trying loop through array , find numbers repeating more once:

e.g: if there 1 1 2 3 4

it should print saying "1 repeats more once"

here code , far have tried, prints duplicates , keep going, if there 4 4 4 4 3 6 5 6 9, print 4's 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]);             }         }     } 

just add number find duplicated structure hashset or hashmap can find later when detect duplication.

set<integer> printed = new hashset<integer>();    for(int i=0; i<buffer.length; i++) {     for(int k=i+1; k<buffer.length; k++) {       if(buffer[k] == buffer[i]) {         integer intobj = new integer(buffer[k]);         if (!printed.contains(intobj)) {           system.out.println(buffer[k]);           printed.add(intobj);         }         break;        }     }   } 

better o(n) alghorithm:

set<integer> printed = new hashset<integer>();    for(int i=0; i<buffer.length; i++) {     if (!printed.add(new integer(buffer[i])) {        system.out.println(buffer[i]);     }   }