CODEWITHSUNDEEP
javacollectionscomparatorinner-classes
Jacob
Jacob

Reputation: 217

Implementing Collections.sort using a comparator defined in a class nested in another class

I have a particular class, let's call it ClassX. ClassX is a simple little class; it has a few data members, a constructor, and (less simply) a nested class. The nested class is specifically for defining a comparator, and is written in this way:

public static Comparator<ClassX> classXComparator = new Comparator<ClassX>()
{
    public int compare(ClassX x1, ClassX x2)
    {
        //code that compares two data members and returns -1 for x2>x1, 1 for x1>x2, 
        //0 for x1 = x2
    }
}

I also have another class, let's call it ClassA. ClassA is the main class of my project, and has an ArrayList of ClassXs called entries. I want to call Collections.sort() on entries; however, I just can't figure out how. The list of things I've tried includes:

I'm stumped. Could someone help me out?

Upvotes: 1

Views: 93

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726639

To understand what's happening look at the declaration of classXComparator:

public static Comparator<ClassX> classXComparator = <something>

This declares classXComparator as a static field of type Comparator<ClassX>, which is precisely the type of the second argument of sort(...). Therefore, the invocation of sort should be as follows:

Collections.sort(entries, ClassX.classXComparator);

Upvotes: 1

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