Implementing a B-tree in java using generics

Question

I have written my own 2-3-4 tree in java. Currently, my code looks like this:

public class tree234{  
    private class node{  
        Comparable data[]=new Comparable[3];  
        node next[]=new node[4];  
    }   
}

Instead, I'd like to have something like this:

public class tree234<T extends Comparable<? super T>>{  
    private class node{  
        T[] data=new T[3];//error here!  
        node[] next=new node[4];  
    }  
}

While I understand that I cannot create the array (and sort of understand why), I can't think of a reasonably simple way to implement the node class with generics. Any suggestions?

Answer 1

You can always do an explicit cast...

The variable T[] will end up as a Comparable[] in the compiled class since T extends Comparable. So the array type must be Comparable[] - you can't assign an Object object to a Comparable variable, .

The other array type is Tree234.Node[].

public class Tree234<T extends Comparable<? super T>>{  
    private class Node{  
        T[] data=(T[]) new Comparable[3];  // need to be a comparable, as the superclass is known.
        Node[] next = (Node[]) new Tree234.Node[4];  

    }  
}