CODEWITHSUNDEEP
javasortingcomparablecompareto
Coffee Maker
Coffee Maker

Reputation: 1573

How to sort objects by different variables?

Can I use a compareTo() method with a second argument to sort objects by different variables, or should I use some other method?

For example:

public class Girl implements Comparable<Girl> {

    private String fName;
    private String lName;
    private int hotness;

    public Girl () {} // blah blah constructor

    @Override
    public int compareTo (Girl g, int order) {
        if (order == 1) // then sort by first name
        if (order == 2) // then sort by last name
        if (order == 3) // then sort by hotness
    }
}

Upvotes: 0

Views: 1191

Answers (3)

Abimaran Kugathasan
Abimaran Kugathasan

Reputation: 32458

You are not overriding the compareTo method, but overloading it. And marking with @Override won't allow to compile the class.

Use multiple Comparator classes to compare Girls based on dirrent scenarios.

Upvotes: 1

yshavit
yshavit

Reputation: 43391

No, you can't. You'll find that code doesn't compile -- the @Override annotation says that compareTo(Girl, int) must be declared in a superclass or interface, but it's not! Comparable<Girl> defines only compareTo(Girl).

Instead, you should use a Comparator<Girl> for each ordering. This is a class that provides its own compareTo that takes two girls. You can then create different comparators, and pass the appropriate one to the function that needs it. In other words, remove the order field from Girl, and instead implement the different orderings as different instances of a Comparator<Girl>.

Most classes or functions that take a T extends Comparable<T> also have versions that take a T and a Comparator<T>. One example of this is Collections.sort. Another is TreeSet, which can take a comparator at construction time.

If that seems annoying or pedantic, think about how you would use such a function. Let's say your function takes a T extends Comparable<T>. You try to compare two of these by calling item1.compareTo(item2), according to that Comparable interface. If your code compiled, that method wouldn't exist! Note that Java doesn't have default parameters, so there's no way to say "if they don't pass in the int order, assume it's 0."

Upvotes: 2

Rahul
Rahul

Reputation: 45040

No, what you're trying to do won't work, as you're not overriding the compareTo() method. An alternate solution here can be to use Collections.sort() to sort your collections with a custom comparator and use the order variable in it(it has to be made final to be able to use it in that). Something like this.

void inSomeMethod() {
    final int order = 0; // has to be final
    Collections.sort(new ArrayList<Girl>(), new Comparator<Girl>() { // for example

        @Override
        public int compare(Girl o1, Girl o2) {
            if (order == 1) // then sort by first name
            if (order == 2) // then sort by last name
            if (order == 3) // then sort by hotness
            return 0;
        }
    });
}

Upvotes: 0

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