Thread: Implementing Multiple Interfaces with Generics

I know that it is possible to force generic parameters to implement certain interfaces like the following:

public class Stuff <E extends Comparable>
{
   //...
}

However, it is not enough for me for E to be Comparable, I also require it to be Cloneable. Is this possible?

Try

public class Stuff <E extends Comparable, Comparable>
{
   //...
}

Originally Posted by copeg

Try

public class Stuff <E extends Comparable, Comparable>
{
   //...
}

The compiler seems to accept <E extends Comparable, Cloneable>, but as soon as it reaches

data = element.clone()

I get:

C:\Users\username\Documents\Programming>javac BSTree.java -Xlint:unchecked
BSTree.java:42: cannot find symbol
symbol  : method clone()
location: interface java.lang.Comparable
                        data = element.clone();
                                      ^
1 error

Originally Posted by helloworld922

Unfortunately, I don't think it's possible directly. What you can do is create your class/interface that sets up which interfaces you want to implement:

public interface ComparableClone<E> extends Comparable<E>, Cloneable
{
     // nothing needed
}

public class Stuff <E extends ComparableClone<?>>
{
     // ...
}

I get nearly the same error, using this implementation as well.

C:\Users\username\Documents\Programming>javac BSTree.java
BSTree.java:42: cannot find symbol
symbol  : method clone()
location: interface ComparableCloneable<capture#594 of ?>
                        data = element.clone();
                                      ^
1 error

Also, I've never seen the ? operator used anywhere other than with ternary operations, what is it's significance when applied to Java Generics?