Java之——利用Comparator接口對多個排序條件進行處理

轉載自：http://blog.csdn.net/l1028386804/article/details/56513205 

膜拜大神···

一、需求

    假設現在有個如此的需求：需要對一個這樣的雇員列表進行排序，排序規則如下：
    1、首先級別最高的排在前面，
    2、如果級別相等，那么按工資排序，工資高的排在前面，
    3、如果工資相當則按入職年數排序，入職時間最長的排在前面。

雇員對象包含級別、工資和入職年份，代碼如下：

 

 package  import   /**
  * 雇員信息
  * @author liuyazhuang
  *
  */ publicclassimplements  privatestaticfinallong       * ID
      */ publicint       * 級別
      */ publicint       * 工資
      */ publicint       * 入職年數
      */ publicint  publicint return   publicvoidint this   publicint return   publicvoidint this   publicint return   publicvoidint this   publicint return   publicvoidint this   publicintintintint this this this this  }

 

二、實現Comparator接口

這里我們實現Java.util.Comparator接口，用於對雇員列表進行排序，代碼如下：

 package  import  import  /**
  * 核心排序類
  * @author liuyazhuang
  *
  */ publicclassimplements
 publicint int;

 int if) {
 ) ?  : -;
 else
  if) {
 ) ?  : -;
 else
  if) {
 ) ?  : -;
    return   }

 

三、驗證排序結果

下面用一個單元測試，來驗證排序結果是否正確

 package  import import import  import  import import  /**
  * 測試排序類
  *
  * @author liuyazhuang
  *
  */ publicclass
 publicvoidthrows new  new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
 new, , , ));
   new );
 );
 for , employee.getId(), employee.getLevel(), employee.getSalary(),
   );
  }

運行結果：

 

四、附錄

java.util.Comparator接口源代碼

 

 /*
  *  Licensed to the Apache Software Foundation (ASF) under one or more
  *  contributor license agreements.  See the NOTICE file distributed with
  *  this work for additional information regarding copyright ownership.
  *  The ASF licenses this file to You under the Apache License, Version 2.0
  *  (the "License"); you may not use this file except in compliance with
  *  the License.  You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  *  Unless required by applicable law or agreed to in writing, software
  *  distributed under the License is distributed on an "AS IS" BASIS,
  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */  package  /**
  * A {@code Comparator} is used to compare two objects to determine their ordering with
  * respect to each other. On a given {@code Collection}, a {@code Comparator} can be used to
  * obtain a sorted {@code Collection} which is <i>totally ordered</i>. For a {@code Comparator}
  * to be <i>consistent with equals</i>, its {code #compare(Object, Object)}
  * method has to return zero for each pair of elements (a,b) where a.equals(b)
  * holds true. It is recommended that a {@code Comparator} implements
  * {@link java.io.Serializable}.
  *
  * @since 1.2
  */ publicinterface       * Compares the two specified objects to determine their relative ordering. The ordering
      * implied by the return value of this method for all possible pairs of
      * {@code (lhs, rhs)} should form an <i>equivalence relation</i>.
      * This means that
      * <ul>
      * <li>{@code compare(a,a)} returns zero for all {@code a}</li>
      * <li>the sign of {@code compare(a,b)} must be the opposite of the sign of {@code
      * compare(b,a)} for all pairs of (a,b)</li>
      * <li>From {@code compare(a,b) > 0} and {@code compare(b,c) > 0} it must
      * follow {@code compare(a,c) > 0} for all possible combinations of {@code
      * (a,b,c)}</li>
      * </ul>
      *
      * @param lhs
      *            an {@code Object}.
      * @param rhs
      *            a second {@code Object} to compare with {@code lhs}.
      * @return an integer < 0 if {@code lhs} is less than {@code rhs}, 0 if they are
      *         equal, and > 0 if {@code lhs} is greater than {@code rhs}.
      * @throws ClassCastException
      *                if objects are not of the correct type.
      */ publicint        * Compares this {@code Comparator} with the specified {@code Object} and indicates whether they
      * are equal. In order to be equal, {@code object} must represent the same object
      * as this instance using a class-specific comparison.
      * <p>
      * A {@code Comparator} never needs to override this method, but may choose so for
      * performance reasons.
      *
      * @param object
      *            the {@code Object} to compare with this comparator.
      * @return boolean {@code true} if specified {@code Object} is the same as this
      *         {@code Object}, and {@code false} otherwise.
      * @see Object#hashCode
      * @see Object#equals
      */ publicboolean }