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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.camel;

/**
 * Used for defining if a given class is singleton or not. If the class is a singleton, then a single instance will be
 * shared (and hence should be treated as immutable and be used in a thread-safe manner).
 * 
 * This interface is not implemented as a marker interface (i.e., it's necessary to read {@link #isSingleton()} instead
 * of instanceof(IsSingleton)). This allows for subclasses to have a singleton status different from a parent
 * and for objects to have this value dynamically changed.
 * 
 * Camel component are very often singleton based, only a few components are not.
 */
public interface IsSingleton {

    /**
     * Test if the given {@code instance} is a singleton or not.
     *
     * @param  instance the instance ot check
     * @return          true if the given {@code instance} is a singleton
     */
    static boolean test(Object instance) {
        return instance instanceof IsSingleton && ((IsSingleton) instance).isSingleton();
    }

    /**
     * Whether this class supports being singleton or not.
     *
     * @return true to be a singleton shared instance, false to create new instances.
     */
    boolean isSingleton();
}