OnJava8-Examples/containers/AdapterMethodIdiom.java

// containers/AdapterMethodIdiom.java
// The "Adapter Method" idiom uses for-in
// with additional kinds of Iterables.
import java.util.*;

class ReversibleArrayList<T> extends ArrayList<T> {
  public ReversibleArrayList(Collection<T> c) { super(c); }
  public Iterable<T> reversed() {
    return () -> new Iterator<T>() {  // <* Describe *>
      int current = size() - 1;
      @Override
      public boolean hasNext() { return current > -1; }
      @Override
      public T next() { return get(current--); }
      @Override
      public void remove() { // Not implemented
        throw new UnsupportedOperationException();
      }
    };
  }
}

public class AdapterMethodIdiom {
  public static void main(String[] args) {
    ReversibleArrayList<String> ral =
      new ReversibleArrayList<>(
        Arrays.asList("To be or not to be".split(" ")));
    // Grabs the ordinary iterator via iterator():
    for(String s : ral)
      System.out.print(s + " ");
    System.out.println();
    // Hand it the Iterable of your choice
    for(String s : ral.reversed())
      System.out.print(s + " ");
  }
}
/* Output:
To be or not to be
be to not or be To
*/