import java.util.ArrayList;
import java.util.HashSet;


public class Test {
    public static void main(String[] args){
        //init
        ArrayList<Integer> a1 = new ArrayList<Integer>();
        ArrayList<Integer> a2 = new ArrayList<Integer>();
        int[] arr1 = new int[]{1,2,3,4};
        int[] arr2 = new int[]{1,2,5,6};
        for(int i = 0;i < arr1.length;++i) a1.add(arr1[i]);
        for(int i = 0;i < arr2.length;++i) a2.add(arr2[i]);
        //get result
        ArrayList<Integer> result = findResult(a1, a2);
        System.out.println(result.toString());
    }

    
    private static ArrayList<Integer> findResult(ArrayList<Integer> a1,ArrayList<Integer> a2){
        @SuppressWarnings("unchecked")
        ArrayList<Integer> result = (ArrayList<Integer>) a1.clone();
        result.removeAll(a2);
        a2.removeAll(a1);
        result.addAll(a2);
        return result;
    }
}