Java: Converting lists of one element type to a list of another type

Question

I\'m writing an adapter framework where I need to convert a list of objects from one class to another. I can iterate through the source list to do this as in

Java: Best

Answer 1

You can write a mapping iterator that decorates an existing iterator and applies a function on it. In this case, the function transforms the objects from one type to another "on-the-fly".

Something like this:

import java.util.*;

abstract class Transformer implements Iterable, Iterator {
    public abstract U apply(T object);  

    final Iterator source;       
    Transformer(Iterable source)    { this.source = source.iterator(); }

    @Override public boolean hasNext() { return source.hasNext(); }
    @Override public U next()          { return apply(source.next()); }
    @Override public void remove()     { source.remove(); } 

    public Iterator iterator()      { return this; }
}

public class TransformingIterator { 
    public static void main(String args[]) {
        List list = Arrays.asList("1", "2", "3");
        Iterable it = new Transformer(list) {
            @Override public Integer apply(String s) {
                return Integer.parseInt(s);
            }
        };
        for (int i : it) {
            System.out.println(i);
        }
    }
}