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.commons.functor.core;
018    
019    import java.io.Serializable;
020    
021    import org.apache.commons.functor.BinaryProcedure;
022    import org.apache.commons.functor.Procedure;
023    import org.apache.commons.functor.UnaryProcedure;
024    
025    /**
026     * A procedure that does nothing at all.
027     * <p>
028     * Note that this class implements {@link Procedure},
029     * {@link UnaryProcedure}, and {@link BinaryProcedure}.
030     * </p>
031     * @version $Revision: 1156349 $ $Date: 2011-08-10 22:21:14 +0200 (Wed, 10 Aug 2011) $
032     * @author Rodney Waldhoff
033     */
034    public final class NoOp implements Procedure, UnaryProcedure<Object>, BinaryProcedure<Object, Object>, Serializable {
035        // static attributes
036        // ------------------------------------------------------------------------
037        /**
038         * Basic NoOp instance.
039         */
040        public static final NoOp INSTANCE = new NoOp();
041        /**
042         * serialVersionUID declaration.
043         */
044        private static final long serialVersionUID = 3768926349922273291L;
045    
046        // constructor
047        // ------------------------------------------------------------------------
048        /**
049         * Create a new NoOp.
050         */
051        public NoOp() {
052        }
053    
054        // predicate interface
055        // ------------------------------------------------------------------------
056        /**
057         * {@inheritDoc}
058         */
059        public void run() {
060        }
061    
062        /**
063         * {@inheritDoc}
064         */
065        public void run(Object obj) {
066        }
067    
068        /**
069         * {@inheritDoc}
070         */
071        public void run(Object left, Object right) {
072        }
073    
074        /**
075         * {@inheritDoc}
076         */
077        public boolean equals(Object that) {
078            return (that instanceof NoOp);
079        }
080    
081        /**
082         * {@inheritDoc}
083         */
084        public int hashCode() {
085            return "NoOp".hashCode();
086        }
087    
088        /**
089         * {@inheritDoc}
090         */
091        public String toString() {
092            return "NoOp";
093        }
094    
095        // static methods
096        // ------------------------------------------------------------------------
097        /**
098         * Get a NoOp instance.
099         * @return NoOp
100         */
101        public static NoOp instance() {
102            return INSTANCE;
103        }
104    
105        /**
106         * Get a typed NoOp {@link UnaryProcedure}.
107         * @param <A> type
108         * @return <code>UnaryProcedure&lt;A&gt;</code>
109         */
110        @SuppressWarnings("unchecked")
111        public static <A> UnaryProcedure<A> unaryInstance() {
112            return (UnaryProcedure<A>) INSTANCE;
113        }
114    
115        /**
116         * Get a typed NoOp {@link BinaryProcedure}.
117         * @param <L> left type
118         * @param <R> right type
119         * @return <code>BinaryProcedure&lt;L, R&gt;</code>
120         */
121        @SuppressWarnings("unchecked")
122        public static <L, R> BinaryProcedure<L, R> binaryInstance() {
123            return (BinaryProcedure<L, R>) INSTANCE;
124        }
125    }