Java Code for finding duplicate element from Arraylist

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

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));
}

}