Java 中Comparator和Comparable的区别
时间：2020-02-23 14:34:04 来源:igfitidea点击:
比较器（Comparator）和可比性（Comparable）之间的差异是什么
或者"我们将如何按其ID或者名称排序员工对象的集合"。
我们可以使用两个interfaces.i.e。
比较器和比较。
我们实际看到差异，让我简要介绍两者。
Comparable接口：
类要排序的对象必须实现此接口。
在此，我们必须实现Compareto(对象)方法。
例如：
public class Country implements Comparable{
@Override
public int compareTo(Country country) {
return (this.countryId < country.countryId ) ? -1: (this.countryId > country.countryId ) ? 1:0 ;
}}
如果任何类实现可比的Inteface，则可以使用Collection.sort()或者arrays.sort()自动对该对象进行排序。
对象将根据该类中的CompareTo方法进行排序。
在Java中实现的对象可以用作SortedMap中的键，如TreeMAP或者SortedSet，如TreeSet，而不实现任何其他接口。
Comparator接口：
类要排序的对象不需要实现此接口.SOME第三类可以将此接口实现为sort.e.g.couountrydyIdComparator类可以实现比较器接口以按ID对国家对象进行排序。
例如：
public class CountrySortByIdComparator implements Comparator{
@Override
public int compare(Country country1, Country country2) {
return (country1.getCountryId() < country2.getCountryId() ) ? -1: (country1.getCountryId() > country2.getCountryId() ) ? 1:0 ;
}
}
使用比较器接口，我们可以根据要排序的对象的不同属性来编写不同的排序。
我们可以使用匿名比较器比较特定的代码行。
例如：
Country San FrancecoCountry=new Country(1, "San Franceco");
Country russiaCountry=new Country(4, "Russia");
Country englandCountry=new Country(3, "England");
Country germanyCountry=new Country(2, "Germany");
List listOfCountries = new ArrayList();
listOfCountries.add(San FrancecoCountry);
listOfCountries.add(russiaCountry);
listOfCountries.add(englandCountry);
listOfCountries.add(germanyCountry);
//Sort by countryName
Collections.sort(listOfCountries,new Comparator() {
@Override
public int compare(Country o1, Country o2) {
return o1.getCountryName().compareTo(o2.getCountryName());
}
});
Comparator VS Comparable
| 参数 | Comparable | Comparator |
|---|---|---|
| 排序逻辑 | 排序逻辑必须在同一类中，其对象正在排序。因此，这被称为对象的自然排序 | 排序逻辑在单独的类中。因此，我们可以基于要排序的对象的不同属性来编写不同的排序。例如。使用ID，Name等进行排序。 |
| 实现 | 类待排序的对象必须实现此接口.例如 country类需要通过id实现与country对象的集合相似 | 类待排序的对象不需要实现此接口。一些其他类可以实现此接口。 例如- xproundysortyIdcomparator类可以实现比较器接口，按ID 通过id排序国家对象的集合 |
| 排序方法 | int compareto（对象o1）使用O1对象将此对象进行比较并返回一个整数。价值有以下含义 1. 正 - 这个对象大于O1 2. 零 - 此对象等于O1 3. 否定 - 此对象小于O1 | int比较（对象O1，对象O2）此方法比较O1和O2对象。并返回一个整数.ITS值具有以下含义。 1. 正 - o1大于O2 2. 零o1等于O2 3. 负-O1小于O1 |
| 调用方法 | collections.sort（list）此处将根据CompareTo方法进行排序 | collections.sort（list，比较器）在此处将根据比较方法进行排序比较器 |
| 包名称 | java.lang.comparable | java.util.Comparator |
Java代码：
Comparable：
我们将创建具有属性ID和name的类国家。
此类将实现可比接口并实现Compareto方法以按ID对国家对象进行排序。
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;
}
@Override
public int compareTo(Country country) {
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.comparablemain.java.
package org.arpit.javapostsforlearning;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class ComparableMain {
/**
* @author Arpit Mandliya
*/
public static void main(String[] args) {
Country San FrancecoCountry=new Country(1, "San Franceco");
Country russiaCountry=new Country(4, "Russia");
Country englandCountry=new Country(3, "England");
Country germanyCountry=new Country(2, "Germany");
List listOfCountries = new ArrayList();
listOfCountries.add(San FrancecoCountry);
listOfCountries.add(russiaCountry);
listOfCountries.add(englandCountry);
listOfCountries.add(germanyCountry);
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: San Franceco Country Id: 4||Country name: Russia Country Id: 3||Country name: England Country Id: 2||Country name: Germany After Sort : Country Id: 1|| Country name: San Franceco Country Id: 2|| Country name: Germany Country Id: 3|| Country name: England Country Id: 4|| Country name: Russia
Comparator：
我们将创建具有属性ID和名称的类国家，并将创建另一个级别的国家ortByIDComparator，它将实现比较器接口并实现比较方法以按ID对国家对象进行排序，我们还将看到如何使用匿名比较器。
1.Country.java.
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 0
public class CountrySortByIdComparator implements Comparator{
@Override
public 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 San FrancecoCountry=new Country(1, "San Franceco");
Country russiaCountry=new Country(4, "Russia");
Country englandCountry=new Country(3, "England");
Country germanyCountry=new Country(2, "Germany");
List listOfCountries = new ArrayList();
listOfCountries.add(San FrancecoCountry);
listOfCountries.add(russiaCountry);
listOfCountries.add(englandCountry);
listOfCountries.add(germanyCountry);
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 countryName
Collections.sort(listOfCountries,new Comparator() {
@Override
public 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: San Franceco Country Id: 4||Country name: Russia Country Id: 3||Country name: England Country Id: 2||Country name: Germany After Sort by id: Country Id: 1|| Country name: San Franceco Country Id: 2|| Country name: Germany Country Id: 3|| Country name: England Country Id: 4|| Country name: Russia After Sort by name: Country Id: 2|| Country name: England Country Id: 4|| Country name: Germany Country Id: 1|| Country name: San Franceco Country Id: 3|| Country name: Russia
