Java List Sorting: Is there a way to keep a list permantly sorted automatically like TreeMap?

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You can change the behaviour of ArrayList

List<MyType> list = new ArrayList<MyType>() {
    public boolean add(MyType mt) {
         super.add(mt);
         Collections.sort(list, comparator);
         return true;
    }
};

Note: a PriorityQueue is NOT a List, if you didn’t care what type of collection it was, the simplest would be to use a TreeSet, which is just like a TreeMap but is a collection. The only advantage PriorityQueue has is to allow duplicates.

Note: resorting is not very efficient for large collections, Using a binary search and inserting an entry would be faster. (but more complicated)

EDIT: A lot depends on what you need the “list” to do. I suggest you write a List wrapper for an ArrayList, LinkedList, PriorityQueue, TreeSet, or one of the other sorted collections and implement the methods which will actually be used. That way you have a good understanding of the requirements for the collection and you can make sure it works correctly for you.

EDIT(2): Since there was so much interest in using binarySearch instead. 😉

List<MyType> list = new ArrayList<MyType>() {
    public boolean add(MyType mt) {
        int index = Collections.binarySearch(this, mt);
        if (index < 0) index = ~index;
        super.add(index, mt);
        return true;
    }
};

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