Re: How do you change all elements in a Collection at the same time?

phillip.s.powell@gmail.com wrote:


Is it the use of iterators or the anonymous inner class syntax bit you
don't understand?

Assuming it's the anonymous inner classes, perhaps it's easier to write
it out in full with an outer class. Obviously this can get much longer,
and hence why inner classes were introduced.

class IncrementTransform implements Transform<Integer>() {
     public Integer transform(Integer value) {
          return value+1;
     }
}
....
         List<Integer> values
            ...
         transform(values, new IncrementTransform());

I would generally recommend creating either a view or a transformed copy
of the data.

Copying we can get rid of the explicit use of iterators.

     public <T> static List<T> transform(
         List<T> src, Transform<T> transform
     ) {
         List<T> dst = new ArrayList<T>(src.size());
             -- The constructor argument is initial capacity, not size.
         for (T value : src) {
             dst.add(transform.transform(value));
         }
         return dst;
     }

Creating a view is more complicated, but has advantages in that client
code doesn't need to handle synchronization to the original data.

class TransformList<T> extends java.util.AbstractList<T> {
     public static <T> List<T> asTransformed(
         List<T> target, Transform<T> transform
     ) {
         return new TransformList<T>(target, transform);
     }

     private final List<T> target;
     private final Transform<T> transform;
     private TransformList(List<T> target, Transform<T> transform) {
         if (target == null || transform == null) {
             throw new NullPointerException();
         }
         this.target = target;
         this.transform = transform;
     }
     public int size() {
         return target.size();
     }
     public T get(int index) {
         return transform.transform(target.get(index));
     }
}

(That code is not the most efficient possible, but should be okay so
long as you don't start using long linked lists.)

Tom Hawtin