CODEWITHSUNDEEP
javagenericscomparable
kurumkan
kurumkan

Reputation: 2725

Can I use <T implements Comparable> or just <Comparable>

Can I use <T implements ..> instead of <T extends...>?

Can't I use <Comparable> just without extends/implements?

Why or why not? 

class SomeClass
{
   public static <T extends Comparable> somemethod(T[] a)
   {
        // do stuff
   }
}

Upvotes: 0

Views: 588

Answers (1)

Elliott Frisch
Elliott Frisch

Reputation: 201467

Comparable is a generic type (and an interface) so you must extend and you cannot implement - it is how Java generics work, also your method is missing a return signature. You could use a Lower Bounded Wildcard like

public static <T extends Comparable<? super T>> T[] somemethod(T... a) {
    Arrays.sort(a);
    return a;
}

which should work as you expect1. For example,

public static void main(String[] args) {
    System.out.println(Arrays.toString(somemethod(4, 3, 1, 2)));
    System.out.println(Arrays.toString(somemethod(new Integer[] { 8, 7, 6, 5 })));
}

Outputs

[1, 2, 3, 4]
[5, 6, 7, 8]

1Here, a variadic (varargs) function that sorts but you can use an array if you like.

Upvotes: 4

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