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 org.apache.commons.functor.BinaryFunction; 020 import org.apache.commons.functor.BinaryPredicate; 021 import org.apache.commons.functor.adapter.BinaryFunctionBinaryPredicate; 022 import org.apache.commons.functor.adapter.IgnoreRightFunction; 023 024 /** 025 * Holder class for a left-identity <code>BinaryFunction</code> (evaluates to the left argument) and a left-identity 026 * <code>BinaryPredicate</code> (tests whether left <code>Boolean</code> argument equals <code>Boolean.TRUE</code>). 027 * 028 * @version $Revision: 1160411 $ $Date: 2011-08-22 22:09:01 +0200 (Mon, 22 Aug 2011) $ 029 * @author Rodney Waldhoff 030 * @author Matt Benson 031 */ 032 public final class LeftIdentity { 033 034 // static attributes 035 // ------------------------------------------------------------------------ 036 /** 037 * Left-identity function. 038 */ 039 public static final BinaryFunction<Object, Object, Object> FUNCTION = LeftIdentity.<Object, Object>function(); 040 041 /** 042 * Left-identity predicate. 043 */ 044 public static final BinaryPredicate<Boolean, Object> PREDICATE = LeftIdentity.<Object>predicate(); 045 046 // constructor 047 // ------------------------------------------------------------------------ 048 /** 049 * Create a new LeftIdentity (for clients that require an object). 050 */ 051 public LeftIdentity() { 052 } 053 054 // static methods 055 // ------------------------------------------------------------------------ 056 057 /** 058 * Get a Left-identity BinaryFunction. 059 * @param <L> the left argument type. 060 * @param <R> the right argument type. 061 * @return BinaryFunction<L, R, L> 062 */ 063 public static <L, R> BinaryFunction<L, R, L> function() { 064 return IgnoreRightFunction.adapt(new Identity<L>()); 065 } 066 067 /** 068 * Get a left-identity BinaryPredicate. 069 * @param <R> the right argument type. 070 * @return BinaryPredicate<Boolean, R> 071 */ 072 public static <R> BinaryPredicate<Boolean, R> predicate() { 073 return BinaryFunctionBinaryPredicate.adapt(IgnoreRightFunction 074 .<Boolean, R, Boolean> adapt(new Identity<Boolean>())); 075 } 076 }