/**
 * A key/value pair.  Useful for association lists and other
 * implementations of dictionaries.  Once you have created a 
 * pair, you cannot change either the key or the value.
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of November 1999
 */
public class Pair {

  // +--------+--------------------------------------------------
  // | Fields |
  // +--------+

  /** The key of the pair. */
  private Object key;

  /** The value in the pair. */
  private Object value;

  // +--------------+--------------------------------------------
  // | Constructors |
  // +--------------+

  /** Build a new key/value pair. */
  public Pair(Object key, Object value) {
    this.key = key;
    this.value = value;
  } // Pair(Object, Object)

  // +---------+-------------------------------------------------
  // | Methods |
  // +---------+

  /** Get the key. */
  public Object getKey() {
    return this.key;
  } // getKey()

  /** Get the value. */
  public Object getValue() {
    return this.value;
  } // getValue()

  /** Determine if another pair has the same key. */
  public boolean equals(Pair other) {
    return this.key.equals(other.key);
  } // equals(Pair)

  /** 
   * Determine if another object is equal to this pair.  The other
   * object must be a pair and an equal pair.
   */
  public boolean equals(Object other) {
    return ( (other instanceof Pair) 
             && (this.equals((Pair) other)) );
  } // equals(Object)

  /**
   * Convert to a string.
   */
  public String toString() {
    return "[" + this.key + "->" + this.value + "]";
  } // toString()
} // class Pair