创建匿名类的对象

Question

We have inner class

class OuterClass
{
  public Iterator getIterator(final String name)
  {
    class LocalIterator implements Iterator
    {
        public Iterator next()
        {
            return new LocalIterator();
        }
    }
    return new LocalIterator();
 }
}

Is it possible to make an anonymous class with all functionality of Local iterator and make getIterator return object of that anonymous class? The main problem is - what should be instead of

  return new LocalIterator();

Answer 1

Im not sure if I understand your question correctly. But if you want to use an anonymous class you can do:

class OuterClass {

    public Iterator<Object> getIterator(final String name) {
        return new Iterator<Object>() {

            @Override
            public boolean hasNext() {
                // validate if there is a next object
                return false;
            }

            @Override
            public Object next() {
                // get the next object and return it, throw an exception if there is no next object
                return null;
            }
        };
    }
}

In general, you are always able to create an instance of any interface using anonymous classes (see, eg, http://docstore.mik.ua/orelly/java-ent/jnut/ch03_12.htm ). You also have access to the name parameter within the class and to the this instance of the outer class using OuterClass.this .

Answer 2

You should give this design pattern a try:

class OuterClass implements Iterable {
    ....

    public Iterator iterator() {
        return new Itr();
    } 

    private class Itr implements Iterator {
        ....
    }
}

1. it doesn't expose iterator implementation
2. it is easy to read and maintain this code
3. Itr instances can be used everywhere as a common Iterator

Answer 3

Make sure OuterClass implements Iterable in order to be usable with the foreach loop. Then in iterator() you could return an instance of an anonymous iterator (replace T with the concrete type you need).

public class OuterClass<T> implements Iterable<T> {

    @Override
    public Iterator<T> iterator() {
        return new Iterator<T>() {

            @Override
            public boolean hasNext() {
                // TODO Auto-generated method stub
                return false;
            }

            @Override
            public T next() {
                // TODO Auto-generated method stub
                return null;
            }
        };
    }
}