Java Comparator syntax works, but why?

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Java inner class and static nested class 23 answers

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SomeClass.PrioritizedPendingListComparator is a class. You need an instance of it so you have to use new

When you define public static class the static means it doesn't implicitly have a reference to the outer class, but you still have to create it in the normal way.

One way to avoid new is to use an enum .

public enum PrioritizedPendingListComparator implements Comparator<SomeClass> {
    INSTANCE;

    @Override
    public int compare(SomeClass o1, SomeClass o2) {
    ...
    }

later

 Collections.sort(pendingList, SomeClass.PrioritizedPendingListComparator.INSTANCE);

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