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 */ 017package org.apache.commons.functor.aggregator.functions; 018 019import org.apache.commons.functor.BinaryFunction; 020 021/** 022 * Aggregator function to be used with subclasses of 023 * {@link org.apache.commons.functor.aggregator.AbstractNoStoreAggregator} which 024 * simply increments the first argument by 1 and returns it. The reason behind 025 * this class is to provide a simple counter implementation: users call 026 * {@link org.apache.commons.functor.aggregator.AbstractNoStoreAggregator#add(Object)} 027 * with some data (which will be ignored) and the class will simply count how 028 * many times this call was made. Such an implementation can be used for 029 * instance to keep track for instance of number of transactions going through a 030 * system, whereas every time a transaction was made we just increment a 031 * counter. This can be achieved still using a 032 * {@link org.apache.commons.functor.aggregator.AbstractNoStoreAggregator} and a 033 * {@link DoubleSumAggregatorBinaryFunction}-like function (but using int) and always 034 * supplying the second parameter as 1 (one). However, using this might make the 035 * code clearer. 036 */ 037public final class IntegerCountAggregatorBinaryFunction implements BinaryFunction<Integer, Integer, Integer> { 038 /** 039 * Increments <code>left</code> by one and returns it. 040 * 041 * @param left 042 * Value to be incremented by 1 and returned. If 043 * <code>null</code>, <code>null</code> is returned. 044 * @param right 045 * ignored 046 * @return <code>left + 1</code> if <code>left != null</code> otherwise it 047 * returns <code>null</code>. 048 */ 049 public Integer evaluate(Integer left, Integer right) { 050 if (left == null) { 051 return null; 052 } 053 return left + 1; 054 } 055 056 @Override 057 public String toString() { 058 return IntegerCountAggregatorBinaryFunction.class.getName(); 059 } 060}