How to set constraints on generic types in Java?

Question

I have a generic class:

public class ListObject<T> {     // fields     protected T _Value = null;       // .. } 

Now I want to do something like the following:

ListObject<MyClass> foo = new ListObject<MyClass>(); ListObject<MyClass> foo2 = new ListObject<MyClass>(); foo.compareTo(foo2); 

Question:

How can I define the compareTo() method with resprect to the generic T?

I guess I have to somehow implement a constraint on the generic T, to tell that T implements a specific interface (maybe Comparable, if that one exists).

Can anyone provide me with a small code sample?

Answer 1

Read also the discussion here: Generics and sorting in Java

Short answer, the best you can get is:

class ListObject<T extends Comparable<? super T>> {     ... } 

But there is also reason to just use:

class ListObject<T extends Comparable> {     ... }