001    // Copyright 2004, 2005 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.hivemind.util;
016    
017    import org.apache.hivemind.HiveMindMessages;
018    
019    /**
020     * Simple utilities for defensive programming.
021     * 
022     * @author Howard M. Lewis Ship
023     * @since 1.1
024     */
025    public final class Defense
026    {
027        private Defense()
028        {
029            // Prevent instantiation
030        }
031    
032        /**
033         * Check for null parameter when not allowed.
034         * 
035         * @throws NullPointerException
036         *             if parameter is null (the message indicates the name of the parameter).
037         */
038        public static void notNull(Object parameter, String parameterName)
039        {
040            if (parameter == null)
041                throw new NullPointerException(HiveMindMessages.paramNotNull(parameterName));
042        }
043        
044        /**
045         * Check for null field value when not allowed.
046         * 
047         * @throws NullPointerException
048         *             if field is null (the message indicates the name of the field).
049         */
050       public static void fieldNotNull(Object value, String fieldName)
051        {
052            if (value == null)
053                throw new NullPointerException(HiveMindMessages.fieldNotNull(fieldName));
054        }
055    
056        /**
057         * Check that a parameter is not null, and assignable to a particular type.
058         * 
059         * @throws ClassCastException
060         *             if not assignable (with a useable message)
061         */
062    
063        public static void isAssignable(Object parameter, Class expectedType, String parameterName)
064        {
065            Defense.notNull(parameter, parameterName);
066    
067            if (!expectedType.isAssignableFrom(parameter.getClass()))
068                throw new ClassCastException(HiveMindMessages.paramWrongType(
069                        parameterName,
070                        parameter,
071                        expectedType));
072        }
073    }