Sort two arrayLists concurrently

Question

Say I have two ArrayLists:

name: [Four, Three, One, Two]
num:  [4, 3, 1, 2]

If I do: Arrays.sort(num), then I have:

name: [         


        

Answer 1

You should somehow associate name and num fields into one class and then have a list of instances of that specific class. In this class, provide a compareTo() method which checks on the numerical values. If you sort the instances, then the name fields will be in the order you desire as well.

class Entity implements Comparable {
    String name;
    int num;
    Entity(String name, int num) {
        this.name = name;
        this.num = num;
    }
    @Override
    public int compareTo(Entity o) {
        if (this.num > o.num)
            return 1;
        else if (this.num < o.num)
            return -1;
        return 0;
    }
}

Test code could be like this:

public static void main(String[] args) {
    List entities = new ArrayList();
    entities.add(new Entity("One", 1));
    entities.add(new Entity("Two", 2));
    entities.add(new Entity("Three", 3));
    entities.add(new Entity("Four", 4));
    Collections.sort(entities);

    for (Entity entity : entities)
        System.out.print(entity.num + " => " + entity.name + " ");
}

Output:

1 => One 2 => Two 3 => Three 4 => Four