Java之——利用Comparator接口对多个排序条件进行处理

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转载自：http://blog.csdn.net/l1028386804/article/details/56513205

膜拜大神···

一、需求

假设现在有个如此的需求：需要对一个这样的雇员列表进行排序，排序规则如下：
1、首先级别最高的排在前面，
2、如果级别相等，那么按工资排序，工资高的排在前面，
3、如果工资相当则按入职年数排序，入职时间最长的排在前面。

雇员对象包含级别、工资和入职年份，代码如下：

[java] view
plain copy

package
import

/**
* 雇员信息
* @author liuyazhuang
*
*/
publicclassimplements
privatestaticfinallong

* ID
*/
publicint
* 级别
*/
publicint
* 工资
*/
publicint
* 入职年数
*/
publicint
publicint
return

publicvoidint
this

publicint
return

publicvoidint
this

publicint
return

publicvoidint
this

publicint
return

publicvoidint
this

publicintintintint
this
this
this
this

}

二、实现Comparator接口

这里我们实现Java.util.Comparator接口，用于对雇员列表进行排序，代码如下：

[java] view
plain copy

package
import

import

/**
* 核心排序类
* @author liuyazhuang
*
*/
publicclassimplements
publicint
int;
int
if) {
) ? : -;
else
if) {
) ? : -;
else
if) {
) ? : -;
return
}

三、验证排序结果

下面用一个单元测试，来验证排序结果是否正确

[java] view
plain copy

package
import
import
import

import

import
import

/**
* 测试排序类
*
* @author liuyazhuang
*
*/
publicclass
publicvoidthrows
new
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new, , , ));
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new
);
);
for
, employee.getId(), employee.getLevel(), employee.getSalary(),
);
}

运行结果：

四、附录

java.util.Comparator接口源代码

[java] view
plain copy

/*
* 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 totally ordered. For a {@code Comparator}
* to be consistent with equals, 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 equivalence relation.
* 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.
*
* 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
}