How do I use Comparator to define a custom sort order?

Question

I want to develop a sorting demo for car list. I am using data table to display car list. Now actually I want to sort the list by car color. Here it is not sort by alphabeti

Answer 1

How about this:

List definedOrder = // define your custom order
    Arrays.asList("Red", "Green", "Magenta", "Silver");

Comparator comparator = new Comparator(){

    @Override
    public int compare(final Car o1, final Car o2){
        // let your comparator look up your car's color in the custom order
        return Integer.valueOf(
            definedOrder.indexOf(o1.getColor()))
            .compareTo(
                Integer.valueOf(
                    definedOrder.indexOf(o2.getColor())));
    }
};

In principle, I agree that using an enum is an even better approach, but this version is more flexible as it lets you define different sort orders.

Update

Guava has this functionality baked into its Ordering class:

List colorOrder = ImmutableList.of("red","green","blue","yellow");
final Ordering colorOrdering = Ordering.explicit(colorOrder);
Comparator comp = new Comparator() {
    @Override
    public int compare(Car o1, Car o2) {
        return colorOrdering.compare(o1.getColor(),o2.getColor());
    }
}; 

This version is a bit less verbose.

---

Update again

Java 8 makes the Comparator even less verbose:

Comparator carComparator = Comparator.comparing(
        c -> definedOrder.indexOf(c.getColor()));