    001// Copyright 2006, 2007 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007//     http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.internal.util;
    016
    017import java.util.concurrent.atomic.AtomicReference;
    018
    019/**
    020 * An object that holds some type of other object. This is useful for communicating information from an inner class
    021 * (used as a closure) to the containing method. This is similar to {@link AtomicReference}, except that it is simpler
    022 * but <strong>not</strong> thread safe.
    023 *
    024 * @param <T> the type being holded.
    025 */
    026public class Holder<T>
    027{
    028    private T held;
    029
    030    public void put(T object)
    031    {
    032        held = object;
    033    }
    034
    035    public T get()
    036    {
    037        return held;
    038    }
    039
    040    public boolean hasValue()
    041    {
    042        return held != null;
    043    }
    044
    045    public static <T> Holder<T> create()
    046    {
    047        return new Holder<T>();
    048    }
    049
    050    public static <T> Holder<T> create(T initial)
    051    {
    052        Holder<T> result = create();
    053        result.put(initial);
    054
    055        return result;
    056    }
    057}