Find max value in Java with a predefined comparator

I have a List<Foo>, and a compare() method taking two Foo objects and returning开发者_开发百科 the 'greater' one. Is there a built-in Java method that takes the list and finds the largest one?

If Foo implements Comparable<Foo>, then Collections.max(Collection) is what you're looking for.

If not, you can create a Comparator<Foo> and use Collections.max(Collection, Comparator) instead.

Example

// Assuming that Foo implements Comparable<Foo>
List<Foo> fooList = ...;
Foo maximum = Collections.max(fooList);
// Normally Foos are compared by the size of their baz, but now we want to
// find the Foo with the largest gimblefleck.
Foo maxGimble = Collections.max(fooList, new Comparator<Foo>() {
    @Override
    public int compare(Foo first, Foo second) {
        if (first.getGimblefleck() > second.getGimblefleck())
            return 1;
        else if (first.getGimblefleck() < second.getGimblefleck())
            return -1;
        return 0;
    }
});

Yes, the List is a subclass of Collection and so you can use the max method.

try java.util.Collections.max

Use Collections#max(Collection).

Assuming Foo is not an inner class and compare() method exists in a class named CompareClass

You can do the following:

Collections.max(fooList, CompareClass::compare);

Which gives the fooList and the method compare as inputs to Collections.max() and returns the Foo object with the max value - according to your compare method.

Take a look at Google Collections - they have lots of methods that help you do this sort of thing using Predicates.

Take a look at lambdaj as well. There are lots of feature to manipulate collection in a functional style.