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    
015    package org.apache.tapestry5.internal.util;
016    
017    import 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>
025     */
026    public 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    }