1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.functor.core; 18 19 import org.apache.commons.functor.BinaryFunction; 20 import org.apache.commons.functor.BinaryPredicate; 21 import org.apache.commons.functor.adapter.BinaryFunctionBinaryPredicate; 22 import org.apache.commons.functor.adapter.IgnoreRightFunction; 23 24 /** 25 * Holder class for a left-identity <code>BinaryFunction</code> (evaluates to the left argument) and a left-identity 26 * <code>BinaryPredicate</code> (tests whether left <code>Boolean</code> argument equals <code>Boolean.TRUE</code>). 27 * 28 * @version $Revision: 1160411 $ $Date: 2011-08-22 22:09:01 +0200 (Mon, 22 Aug 2011) $ 29 * @author Rodney Waldhoff 30 * @author Matt Benson 31 */ 32 public final class LeftIdentity { 33 34 // static attributes 35 // ------------------------------------------------------------------------ 36 /** 37 * Left-identity function. 38 */ 39 public static final BinaryFunction<Object, Object, Object> FUNCTION = LeftIdentity.<Object, Object>function(); 40 41 /** 42 * Left-identity predicate. 43 */ 44 public static final BinaryPredicate<Boolean, Object> PREDICATE = LeftIdentity.<Object>predicate(); 45 46 // constructor 47 // ------------------------------------------------------------------------ 48 /** 49 * Create a new LeftIdentity (for clients that require an object). 50 */ 51 public LeftIdentity() { 52 } 53 54 // static methods 55 // ------------------------------------------------------------------------ 56 57 /** 58 * Get a Left-identity BinaryFunction. 59 * @param <L> the left argument type. 60 * @param <R> the right argument type. 61 * @return BinaryFunction<L, R, L> 62 */ 63 public static <L, R> BinaryFunction<L, R, L> function() { 64 return IgnoreRightFunction.adapt(new Identity<L>()); 65 } 66 67 /** 68 * Get a left-identity BinaryPredicate. 69 * @param <R> the right argument type. 70 * @return BinaryPredicate<Boolean, R> 71 */ 72 public static <R> BinaryPredicate<Boolean, R> predicate() { 73 return BinaryFunctionBinaryPredicate.adapt(IgnoreRightFunction 74 .<Boolean, R, Boolean> adapt(new Identity<Boolean>())); 75 } 76 }