001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.camel;
018    
019    /**
020     * Used for defining if a given class is singleton or not.  If the class is a singleton, 
021     * then a single instance will be shared (and hence should be treated as immutable and
022     * be used in a thread-safe manner).
023     * <p/>
024     * This interface is not implemented as a marker interface (i.e., it's necessary to read  
025     * {@link #isSingleton()} instead of <tt>instanceof(IsSingleton))</tt>.
026     * This allows for subclasses to have a singleton status different from a parent and
027     * for objects to have this value dynamically changed.
028     * <p/>
029     * Camel component is very often singleton based, only a few components is not.
030     *
031     * @version 
032     */
033    public interface IsSingleton {
034    
035        /**
036         * Whether this class supports being singleton or not.
037         *
038         * @return <tt>true</tt> to be a single shared instance, <tt>false</tt> to create new instances.
039         */
040        boolean isSingleton();
041    
042    }