Java Program for finding duplicate element from ArrayList ?

Previously we have discussed the Program for 
Java Program Without Main Method ?

In Method 1 we are using set interface to find duplicate element from list because Set Interface only allow unique elements , In Method 2 we are using for loop to find duplicate element .

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class DuplicateSingleElementFromList {

static int method1(List<Integer> list){
 int duplicate = 0;
 Set<Integer> set = new HashSet<>();
 for(int i=0;i<list.size();i++){
  if(!set.add(list.get(i))){
   duplicate = list.get(i);
   break;
  }
 }
 return duplicate;
}
static int method2(List<Integer> list){
 int duplicate = 0;
 for(int i=0;i<list.size();i++){
  for(int j=1;j<list.size();j++){
   if(list.get(i) == list.get(j)){
    duplicate = list.get(i);
    break;
   }
  }
 }
 return duplicate;
}
public static void main(String[] args) {
 List<Integer> list = new ArrayList<>();
 for(int i=0;i<100;i++){
 list.add(i);
 }
 list.add(11);
 System.out.println("METHOD 1 OUTPUT : "+method1(list));
 System.out.println("METHOD 2 OUTPUT : "+method2(list));
}

}

Program Output :-

METHOD 1 OUTPUT : 11
METHOD 2 OUTPUT : 11