/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
* See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
*/
package org.hibernate.internal.util;
/**
* Represents a "final" value that is initialized either {@link #ValueHolder(Object) up front} or once at some point
* {@link #ValueHolder(ValueHolder.DeferredInitializer) after} declaration.
*
* Note: If a Serializable class has a {@link ValueHolder} property, that property should be declared transient!
*
* @author Steve Ebersole
*/
public class ValueHolder<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 ValueHolder} with the specified initializer.
*
* @param valueInitializer The initializer to use in {@link #getValue} when value not yet known.
*/
public ValueHolder(DeferredInitializer<T> valueInitializer) {
this.valueInitializer = valueInitializer;
}
@SuppressWarnings( {"unchecked"})
public ValueHolder(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 Void initialize() {
return null;
}
};
}