Java泛型比较器

Question

I am coding with Java Generics. I want to define a Binary Tree class generically that will be able to take in any class , and guarantee that that class has the Comparator method compare(T o1, T o2) to see whether I need to follow the right or left subtree for insert into my binary tree.

public class treeDB <T implements Comparator> {
    //define my binary tree methods
}

That is my best estimation of how to force to implement Comparator method, but the compile throws an error and I don't know enough to know what it wants.

Answer 1

try this

class treeDB <T extends Comparator<T>> {
...

Answer 2

Everyone has provided the correct syntax, but you might want to consider using Comparable as in

class treeDB <T extends Comparable<T>>

The differences are subtle, and maybe it isn't the better choice. But it never hurts to look.

Answer 3

Firstly, implements should be replaced with extends . In generics extends is the keyword which is used even if the generic type implements an interface.

And secondly, using only Comparator will result in a warning it being a raw type. You must parameterize it. This is your solution:

public class treeDB <T extends Comparator<T>> {

}

Answer 4

这应该是public class treeDB <T extends Comparator> ，而不是public class treeDB <T implements Comparator> 。