如何使用扩展类 <E extends Comparable<E> &gt;

Question

I'm trying to make an abstract class AbstractBinSearchTree like this:

public abstract class AbstractBinSearchTree<E extends Comparable<E>>
{ 
   public abstract void add(E element);
   public abstract void add(Collection<E> elemente);

   public List<E> retrieveInOrder(Pos<E> p) {
   ...
   }

My question is now how to extend from this class. I want to make an ArrayBinTreeSearch which I can instantiate like this:

AbstractBinSearchTree<Elem> tree = new ArrayBinSearchTree<Elem>();

I tried this:

public class ArrayBinSearchTree<E extends Comparable<? super E>> extends AbstractBinSearchTree<Comparable<E>>{

Comparable<E>[] _tree;

public ArrayBinSearchTree(int size)
{
    _tree = new Comparable[size];
}

@SuppressWarnings("unchecked")
@Override
public void add(Comparable<?> element) {
    ...
}

But I doesn't really feel like this is the correct way to use it. Also I cannot instantiate like I mentioned above.

Answer 1

I believe you need to replace the following line:

public class ArrayBinSearchTree<E extends Comparable<? super E>> extends AbstractBinSearchTree<Comparable<E>>{

With:

public class ArrayBinSearchTree<E extends Comparable<? super E>> extends AbstractBinSearchTree<E>{

Otherwise you'll restrict the parameters of any methods in AbstractBinSearchTree . In addition, expand the generic type of AbstractBinSearchTree as follows:

public abstract class AbstractBinSearchTree<E extends Comparable<? super E>>

Also, your ArrayBinSearchTree constructor has an int parameter:

AbstractBinSearchTree<Elem> tree = new ArrayBinSearchTree<Elem>(5);

And can be replaced by diamond syntax:

AbstractBinSearchTree<Elem> tree = new ArrayBinSearchTree<>(5);

Assuming you're using Java 7 or higher

Answer 2

与它的界面相当，然后必须将“扩展”更改为“实现”