Union and Intersection

This question was asked in the first coding round on-site. 

Give two sorted lists List<Integer> a and List<Integer> b. 

Find 
the Union of these two lists -> the union list should also be sorted 
the Intersection of these two lists -> Intersection list should also be sorted.

public class UnionIntersection {
    static void Main(String[] args )
    { 
        ArrayList<Integer> l1 = new ArrayList<Integer>();
        ArrayList<Integer> l2 = new ArrayList<Integer>();
        l1.add(1);
        l1.add(23);
        l1.add(26);
        l1.add(40);
        l1.add(45);
        l2.add(-1);        
        l2.add(2);
        l2.add(6);
        l2.add(26);
        l2.add(40);
        l2.add(50);
        l2.add(75);
        
    
        for(int val: union( l1, l2 ) )
            System.out.print( val + " " );

        System.out.println();

        for(int val: intersect( l1, l2 ) )
            System.out.print( val + " " );

    }

    private static ArrayList<Integer> union( ArrayList<Integer> l1, ArrayList<Integer> l2 )
    {
        if ( l1.size() == 0 )
            return l2;
        if ( l2.size() == 0 )
            return l1;

        ArrayList<Integer> op = new ArrayList<Integer>();

        int start1 = 0;
        int start2 = 0;

        int end1 = l1.size();
        int end2 = l2.size();

        while ( start1 < end1 && start2 < end2 )
        {
            if (l1.get(start1) <= l2.get(start2))
            {
                op.add(l1.get(start1));
                start1++;
            }
            else
            {
                op.add(l2.get(start2));
                start2++;
            }
        }

        if ( start1 == end1 )
        {
            while ( start2 < end2 )
            {
                op.add(l2.get(start2));
                start2++;
            }
        }
        if ( start2 == end2 )
        {
            while ( start1 < end1 )
            {
                op.add(l1.get(start1));
                start1++;
            }
        }
        return op;
    }
    
    public static ArrayList<Integer> intersect( ArrayList<Integer> l1, ArrayList<Integer> l2 )
    {
        if ( l1.size() == 0 )
            return l2;
        if ( l2.size() == 0 )
            return l1;

        ArrayList<Integer> op = new ArrayList<Integer>();

        int start1 = 0;
        int start2 = 0;

        int end1 = l1.size();
        int end2 = l2.size();

        while ( start1 < end1 && start2 < end2 )
        {
            if ( l1.get(start1) == l2.get(start2) )
            {
                op.add(l1.get(start1));
                start1++;
                start2++;
            }
            else if ( l1.get(start1) < l2.get(start2) )
            {
                start1++;
                continue;
            }
            else
            {
                start2++;
            }
        }
        return op;
    }
}