gistfile1.txt

public class Value<T> {

	/**
	 * The snippet that generates the initialization value.
	 *
	 * @param <T>
	 */
	public static interface DeferredInitializer<T> {
		/**
		 * Build the initialization value.
		 * <p/>
		 * Implementation note: returning {@code null} is "ok" but will cause this method to keep being called.
		 *
		 * @return The initialization value.
		 */
		public T initialize();
	}

	private final DeferredInitializer<T> valueInitializer;
	private T value;

	/**
	 * Instantiates a {@link Value} with the specified initializer.
	 *
	 * @param valueInitializer The initializer to use in {@link #getValue} when value not yet known.
	 */
	public Value(DeferredInitializer<T> valueInitializer) {
		this.valueInitializer = valueInitializer;
	}

	@SuppressWarnings( {"unchecked"})
	public Value(T value) {
		this( NO_DEFERRED_INITIALIZER );
		this.value = value;
	}

	public T getValue() {
		if ( value == null ) {
			value = valueInitializer.initialize();
		}
		return value;
	}

	private static final DeferredInitializer NO_DEFERRED_INITIALIZER = new DeferredInitializer() {
		@Override
		public Object initialize() {
			return null;
		}
	};
}