getOnlyElement

A.java

import com.google.common.base.Optional;
import com.google.common.collect.Lists;
import java.util.Iterator;
import java.util.NoSuchElementException;

public class A {
  public static <T> T getOnlyElement(Iterable<T> xs, Optional<T> e, Optional<T> xx) {
    Iterator<T> i = xs.iterator();
    if (!i.hasNext()) {
      if (e.isPresent()) return e.get();
      throw new NoSuchElementException();
    }
    T r = i.next();
    if (i.hasNext()) {
      if (xx.isPresent()) return xx.get();
      throw new IllegalArgumentException();
    }
    return r;
  }
  public static <T> T getOnlyElement(Iterable<T> xs) {
    return getOnlyElement(xs, Optional.<T>absent(), Optional.<T>absent());
  }
  public static <T> T getOnlyElement(Iterable<T> xs, T d) {
    return getOnlyElement(xs, Optional.of(d), Optional.<T>absent());
  }
  public static <T> T getOnlyElement(Iterable<T> xs, T d1, T d2) {
    return getOnlyElement(xs, Optional.of(d1), Optional.of(d2));
  }

  public static String describe(Iterable<String> xs) {
    return getOnlyElement(xs, "none", "all");
  }
  public static void main(String[] args) {
    System.out.printf("processing %s%n", describe(Lists.newArrayList(args)));
  }
}