SinglePropertyMap.java

package com.thaiopensource.util;

public class SinglePropertyMap<T> implements PropertyMap {
  private final PropertyId<T> pid;
  private final T value;

  private SinglePropertyMap(PropertyId<T> pid, T value) {
    if (!(pid.getValueClass().isInstance(value))) {
      if (value == null)
        throw new NullPointerException();
      throw new ClassCastException();
    }
    this.pid = pid;
    this.value = value;
  }

  public <V> V get(PropertyId<V> pid) {
    if (pid != this.pid)
      return null;
    // it would be nice to avoid the cast,
    // but I can't figure out how to do it
    return pid.getValueClass().cast(value);
  }

  public boolean contains(PropertyId<?> pid) {
    return pid == this.pid;
  }

  public int size() {
    return 1;
  }

  public PropertyId<?> getKey(int i) {
    if (i != 0)
      throw new IndexOutOfBoundsException();
    return pid;
  }

  public static <T> SinglePropertyMap newInstance(PropertyId<T> pid, T value) {
    return new SinglePropertyMap<T>(pid, value);
  }
}