Immutable pair of elements. I have used this in many projects, too bad the Java library does not include it by default.

Pair.java

package util;

public class Pair<T extends Comparable<T>, U extends Comparable<U>> implements Comparable<Pair<T,U>> {
  private T first;
  private U second;

  public Pair(T first, U second) {
    if (first == null) throw new IllegalArgumentException("First argument must not be null");
    if (second == null) throw new IllegalArgumentException("Second argument must not be null");
    this.first = first;
    this.second = second;
  }

  public T getFirst() {
    return first;
  }

  public U getSecond() {
    return second;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + first.hashCode();
    result = prime * result + second.hashCode();
    return result;
  }

  @Override
  @SuppressWarnings("unchecked")
  public boolean equals(Object obj) {
    if (this == obj) return true;
    if (obj == null) return false;
    if (getClass() != obj.getClass()) return false;
    Pair<T,U> other = (Pair<T,U>) obj;

    return first.equals(other.first) && second.equals(other.second);
  }

  @Override
  public int compareTo(Pair<T, U> other) {
    final int diff = first.compareTo(other.first);
    if (diff != 0) return diff;
    return second.compareTo(other.second);
  }

  public static <T extends Comparable<T>, U extends Comparable<U>> Pair<T,U> pair(T first, U second) {
    return new Pair<T,U>(first, second);
  }
}