在本教程中，我们将看到如何在Java中使用Comparable给对象列表排序。

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。

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

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.theitroad;
//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.theitroad;
 
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 chinaCountry=new Country(4, "China");
		Country nepalCountry=new Country(3, "Nepal");
		Country bhutanCountry=new Country(2, "Bhutan");
 
		List listOfCountries = new ArrayList();
		listOfCountries.add(San FrancecoCountry);
		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: San Franceco
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: San Franceco
Country Id: 2|| Country name: Bhutan
Country Id: 3|| Country name: Nepal
Country Id: 4|| Country name: China