Java中Comparator和Comparable之间的区别

常见的面试问题之一是“比较器和可比较器之间有什么区别”。或“您将如何通过其ID或名称对员工对象集合进行排序”。为此，我们可以使用两个接口，即Comparator和Comparable。在我们真正看到差异之前，让我简要介绍一下两者。

可比接口：要对其进行排序的对象的类必须实现此接口。在此，我们必须实现compareTo（Object）方法。

例如：

public class Country implements Comparable{@Overridepublic int compareTo(Object arg0) {Country country=(Country) arg0;return (this.countryId < country.countryId ) ? -1: (this.countryId > country.countryId ) ? 1:0 ;
}}

如果任何类实现可比较的接口，则可以使用Collection.sort（）或Arrays.sort（）自动对该对象的集合进行排序。对象将基于该类中的compareTo方法进行排序。

在Java中实现Comparable的对象可以用作SortedMap（如TreeMap）或SortedSet（如TreeSet）中的键，而无需实现任何其他接口。

Comparator接口：需要对其进行排序的对象的类无需实现此接口。某些第三类可以实现此接口进行排序。egCountrySortByIdComparator类可以实现Comparator接口以按ID对国家对象的集合进行排序。例如：

public class CountrySortByIdComparator implements Comparator<Country>{@Overridepublic int compare(Country country1, Country country2) {return (country1.getCountryId() < country2.getCountryId() ) ? -1: (country1.getCountryId() > country2.getCountryId() ) ? 1:0 ;}}

使用Comparator界面，我们可以根据要排序的对象的不同属性编写不同的排序。您可以使用匿名比较器在特定代码行进行比较。例如：

Country indiaCountry=new Country(1, 'India');Country chinaCountry=new Country(4, 'China');Country nepalCountry=new Country(3, 'Nepal');Country bhutanCountry=new Country(2, 'Bhutan');List<Country> listOfCountries = new ArrayList<Country>();listOfCountries.add(indiaCountry);listOfCountries.add(chinaCountry);listOfCountries.add(nepalCountry);listOfCountries.add(bhutanCountry); //Sort by countryNameCollections.sort(listOfCountries,new Comparator<Country>() {@Overridepublic int compare(Country o1, Country o2) {return o1.getCountryName().compareTo(o2.getCountryName());}});

比较器vs可比

参数	可比	比较器
排序逻辑	排序逻辑必须在要对其对象进行排序的同一类中。因此，这称为对象的自然排序	排序逻辑在单独的类中。因此，我们可以根据要排序的对象的不同属性编写不同的排序。例如，使用ID，名称等进行排序
实作	对其对象进行排序的类必须实现此接口。例如Country类需要实现与id对应的country对象的收集类似的实现	要排序对象的类不需要实现此接口。其他一些类也可以实现此接口。 Eg-CountrySortByIdComparator类可以实现Comparator接口，以按ID对国家/地区对象的集合进行排序
排序方式	int compareTo（Object o1）该方法将该对象与o1对象进行比较并返回一个整数，其值具有以下含义 1.正数–该对象大于o1 2.零–此对象等于o1 3.负数–该对象小于o1	int compare（对象o1，对象o2）此方法比较o1和o2对象。并返回一个整数。其值具有以下含义。 1.正数– o1大于o2 2.零– o1等于o2 3.负数– o1小于o1
调用方式	Collections.sort（列表）在这里，对象将根据CompareTo方法进行排序	Collections.sort（列表，比较器）在这里，对象将根据Comparator中的Compare方法进行排序
包	Java.lang.Comparable	Java.util.Comparator

Java代码：
对于Comparable：我们将创建具有属性ID和名称的country类，该类将实现Comparable接口并实现CompareTo方法以按ID对国家对象的集合进行排序。

1. Country.java

package org.arpit.javapostsforlearning;
//If this.cuntryId < country.countryId:then compare method will return -1
//If this.countryId > country.countryId:then compare method will return 1
//If this.countryId==country.countryId:then compare method will return 0
public class Country implements Comparable{int countryId;String countryName;public Country(int countryId, String countryName) {super();this.countryId = countryId;this.countryName = countryName;}@Overridepublic int compareTo(Object arg0) {Country country=(Country) arg0;return (this.countryId < country.countryId ) ? -1: (this.countryId > country.countryId ) ? 1:0 ;}public int getCountryId() {return countryId;}public void setCountryId(int countryId) {this.countryId = countryId;}public String getCountryName() {return countryName;}public void setCountryName(String countryName) {this.countryName = countryName;}}

2.ComparatorMain.java

package org.arpit.javapostsforlearning;import java.util.ArrayList;
import java.util.Collections;
import java.util.List;public class ComparatorMain {/*** @author Arpit Mandliya*/public static void main(String[] args) {Country indiaCountry=new Country(1, 'India');Country chinaCountry=new Country(4, 'China');Country nepalCountry=new Country(3, 'Nepal');Country bhutanCountry=new Country(2, 'Bhutan');List<Country> listOfCountries = new ArrayList<Country>();listOfCountries.add(indiaCountry);listOfCountries.add(chinaCountry);listOfCountries.add(nepalCountry);listOfCountries.add(bhutanCountry);System.out.println('Before Sort  : ');for (int i = 0; i < listOfCountries.size(); i++) {Country country=(Country) listOfCountries.get(i);System.out.println('Country Id: '+country.getCountryId()+'||'+'Country name: '+country.getCountryName());}Collections.sort(listOfCountries);System.out.println('After Sort  : ');for (int i = 0; i < listOfCountries.size(); i++) {Country country=(Country) listOfCountries.get(i);System.out.println('Country Id: '+country.getCountryId()+'|| '+'Country name: '+country.getCountryName());}}}

输出：

Before Sort  : 
Country Id: 1||Country name: India
Country Id: 4||Country name: China
Country Id: 3||Country name: Nepal
Country Id: 2||Country name: Bhutan
After Sort  : 
Country Id: 1|| Country name: India
Country Id: 2|| Country name: Bhutan
Country Id: 3|| Country name: Nepal
Country Id: 4|| Country name: China

对于Comparator：我们将创建具有属性ID和名称的country类，并创建另一个CountryAortByIdComparator类，该类将实现Comparator接口并实现compare方法以按ID对国家对象的集合进行排序，并且还将看到如何使用匿名比较器。

1.国家/地区

package org.arpit.javapostsforlearning;public class Country{int countryId;String countryName;public Country(int countryId, String countryName) {super();this.countryId = countryId;this.countryName = countryName;}public int getCountryId() {return countryId;}public void setCountryId(int countryId) {this.countryId = countryId;}public String getCountryName() {return countryName;}public void setCountryName(String countryName) {this.countryName = countryName;}}

2.CountrySortbyIdComparator.java

package org.arpit.javapostsforlearning;import java.util.Comparator;
//If country1.getCountryId()<country2.getCountryId():then compare method will return -1
//If country1.getCountryId()>country2.getCountryId():then compare method will return 1
//If country1.getCountryId()==country2.getCountryId():then compare method will return 0public class CountrySortByIdComparator implements Comparator<Country>{@Overridepublic int compare(Country country1, Country country2) {return (country1.getCountryId() < country2.getCountryId() ) ? -1: (country1.getCountryId() > country2.getCountryId() ) ? 1:0 ;}}

3，ComparatorMain.java

package org.arpit.javapostsforlearning;import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;public class ComparatorMain {/*** @author Arpit Mandliya*/public static void main(String[] args) {Country indiaCountry=new Country(1, 'India');Country chinaCountry=new Country(4, 'China');Country nepalCountry=new Country(3, 'Nepal');Country bhutanCountry=new Country(2, 'Bhutan');List<Country> listOfCountries = new ArrayList<Country>();listOfCountries.add(indiaCountry);listOfCountries.add(chinaCountry);listOfCountries.add(nepalCountry);listOfCountries.add(bhutanCountry);System.out.println('Before Sort by id : ');for (int i = 0; i < listOfCountries.size(); i++) {Country country=(Country) listOfCountries.get(i);System.out.println('Country Id: '+country.getCountryId()+'||'+'Country name: '+country.getCountryName());}Collections.sort(listOfCountries,new CountrySortByIdComparator());System.out.println('After Sort by id: ');for (int i = 0; i < listOfCountries.size(); i++) {Country country=(Country) listOfCountries.get(i);System.out.println('Country Id: '+country.getCountryId()+'|| '+'Country name: '+country.getCountryName());}//Sort by countryNameCollections.sort(listOfCountries,new Comparator<Country>() {@Overridepublic int compare(Country o1, Country o2) {return o1.getCountryName().compareTo(o2.getCountryName());}});System.out.println('After Sort by name: ');for (int i = 0; i < listOfCountries.size(); i++) {Country country=(Country) listOfCountries.get(i);System.out.println('Country Id: '+country.getCountryId()+'|| '+'Country name: '+country.getCountryName());}}}

输出：

Before Sort by id : 
Country Id: 1||Country name: India
Country Id: 4||Country name: China
Country Id: 3||Country name: Nepal
Country Id: 2||Country name: Bhutan
After Sort by id: 
Country Id: 1|| Country name: India
Country Id: 2|| Country name: Bhutan
Country Id: 3|| Country name: Nepal
Country Id: 4|| Country name: China
After Sort by name: 
Country Id: 2|| Country name: Bhutan
Country Id: 4|| Country name: China
Country Id: 1|| Country name: India
Country Id: 3|| Country name: Nepal

参考： JCG合作伙伴 Arpit Mandliya在Java框架和面向初学者博客的设计模式中的比较器与Java中的Comparable之间的区别。