CODEWITHSUNDEEP
javasortingarraylist
Josh Beckwith
Josh Beckwith

Reputation: 1540

Java, sort arraylist by custom alpha order

Let's say I have

arrayList<String> fruits

that contains

{"banana", "apple", "grape", "banana", "banana", "grape"}

I know how to sort these alphabetically by using a comparator (below) :

Collections.sort(fruits, new Comparator<Fruit>() {
        public int compare(Fruit o1, Fruit o2) {
            return o1.getName().compareTo(o2.getName());
        }
    });

However that would give me {"apple", "banana", "banana", "banana", "grape", "grape"}. How would I change this so I get all the bananas listed first, then apples, then grapes? Thanks!

Upvotes: 1

Views: 169

Answers (2)

MigSena
MigSena

Reputation: 218

You may first create your custom comparator like that :

public static class CustomFruitComparator implements Comparator<String> {

    Map<String, Integer> fruitsOrder;

    public CustomFruitComparator(Map<String, Integer> fruitsOrder) {
        this.fruitsOrder = fruitsOrder;
    }

    @Override
    public int compare(String o1, String o2) {
        if (fruitsOrder.get(o1) > fruitsOrder.get(o2))
            return 1;
        else if (fruitsOrder.get(o1) < fruitsOrder.get(o2))
            return -1;
        return 0;
    }

}

And then you can use it to sort your collection. In your case, you can do like that : 

List<String> fruits = Arrays.asList(new String[]{"banana", "apple", "grape", "banana", "banana", "grape"});

    Map<String, Integer> fruitsOrder = new HashMap<>();
    fruitsOrder.put("banana", 1);
    fruitsOrder.put("apple", 2);
    fruitsOrder.put("grape", 3);

    Collections.sort(fruits, new CustomFruitComparator(fruitsOrder));

Upvotes: 0

Patrick Parker
Patrick Parker

Reputation: 4959

This might help get you started:

List<String> fruitsOrder = Arrays.asList(new String[]{"banana","apple","grape"});
Comparator<String> c = Comparator.comparingInt(str -> fruitsOrder.indexOf(str));

You could refine it further, by normalizing the case, and/or by using Comparator.thenComparing, to have a consistent order for fruits not in the list.

Upvotes: 3

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