Question

I have two Arraylists:

ArrayList a1 = new ArrayList();
a1.add("5");
a1.add("10");
a1.add("20");
a1.add("50");
a1.add("100");
a1.add("500");
a1.add("1000");

ArrayList a2 = new ArrayList();
a2.add("50");
a2.add("500");
a2.add("1000");

How can I compare this two arraylists and add into new arraylist(a3) with 1 if a2 exist in a1 and 0 if not exist, so the result will below for arraylist a3?

a3[0] = 0
a3[1] = 0
a3[2] = 0
a3[3] = 1
a3[4] = 0
a3[5] = 1
a3[6] = 1

Thanks in advance

Answer 1

First, I would advice you to use generics. And secondly, for a2 could be a Set instead. And thirdly you might want to change from String to Integer (since they are all integers).

But for your example this is a way to do it:

ArrayList<Integer> a3 = new ArrayList<Integer>();               
for (String a : a1)
    a3.add(a2.contains(a) ? 1 : 0);

---

Full example (with a HashSet and Integer type):

public static void main(String... args) {
    List<Integer> a1 = Arrays.asList(5, 10, 20, 50, 100, 500, 1000);
    Set<Integer>  a2 = new HashSet<Integer>(Arrays.asList(50, 500, 1000));

    ArrayList<Integer> a3 = new ArrayList<Integer>();                

    for (Integer a : a1)
        a3.add(a2.contains(a) ? 1 : 0);

    System.out.println(a3);
}

Output:

[0, 0, 0, 1, 0, 1, 1]