Comparable与Comparator之区别与使用

Comparable接口强行对实现它的每个类的对象进行整体排序。此排序被称为该类的自然排序，类的 compareTo 方法被称为它的自然比较方法。实现此接口的对象列表（和数组）可以通过Collections.sort（和 Arrays.sort）进行自动排序。实现此接口的对象可以用作有序映射表中的键或有序集合中的元素，无需指定比较器。

Comparator比较函数强行对某些对象 collection 进行整体排序。可以将 Comparator 传递给 sort 方法（如 Collections.sort），从而允许在排序顺序上实现精确控制。还可以使用 Comparator 来控制某些数据结构（如 TreeSet 或 TreeMap）的顺序。

以下为一个人的排序实例:

package com.lyh.util.compar;
import java.util.Comparator;
//实现按FirstName进行排序
public class FirstNameComparator implements Comparator {
public FirstNameComparator() {
         // TODO Auto-generated constructor stub
}
public int compare(Object person, Object anotherPerson) {
         // TODO Auto-generated method stub
             String lastName1 = ((Person) person).getLastName().toUpperCase();
             String firstName1 = ((Person) person).getFirstName().toUpperCase();
             String lastName2 = ((Person) anotherPerson).getLastName().toUpperCase();
             String firstName2 = ((Person) anotherPerson).getFirstName().toUpperCase();
      
             if (firstName1.equals(firstName2)) {
                 return lastName1.compareTo(lastName2);
               } else {
                 return firstName1.compareTo(firstName2);
               }
}

}
//实现按LastName进行排序

package com.lyh.util.compar;

import java.util.Comparator;

public class LastNameComparator implements Comparator {

public int compare(Object person, Object anotherPerson) {
         String lastName1 = ((Person) person).getLastName().toUpperCase();
         String firstName1 = ((Person) person).getFirstName().toUpperCase();
         String lastName2 = ((Person) anotherPerson).getLastName().toUpperCase();
         String firstName2 = ((Person) anotherPerson).getFirstName()
           .toUpperCase();

         if (lastName1.equals(lastName2)) {
          return firstName1.compareTo(firstName2);
         } else {
          return lastName2.compareTo(lastName1);
         }
}

}

//Person类

package com.lyh.util.compar;

public class Person implements Comparable {
private String firstName;

private String lastName;

private int age;

public int getAge() {
         return age;
}

public void setAge(int age) {
         this.age = age;
}

public String getFirstName() {
         return firstName;
}

public void setFirstName(String firstName) {
         this.firstName = firstName;
}

public String getLastName() {
         return lastName;
}

public void setLastName(String lastName) {
         this.lastName = lastName;
}

public int compareTo(Object anotherPerson) {
         // TODO Auto-generated method stub
         if (!(anotherPerson instanceof Person)) {
               throw new ClassCastException("A Person object expected.");
             }
             int anotherPersonAge = ((Person) anotherPerson).getAge();
             return this.age - anotherPersonAge;

}

}

//主函数
package com.lyh.util.compar;

import java.util.Arrays;

public class MainClass {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
         // TODO Auto-generated method stub
         Person[] persons = new Person[4];
            persons[0] = new Person();
            persons[0].setFirstName("A");
            persons[0].setLastName("X");
            persons[0].setAge(56);

            persons[1] = new Person();
            persons[1].setFirstName("S");
            persons[1].setLastName("C");
            persons[1].setAge(8);

            persons[2] = new Person();
            persons[2].setFirstName("E");
            persons[2].setLastName("H");
            persons[2].setAge(16);

            persons[3] = new Person();
            persons[3].setFirstName("B");
            persons[3].setLastName("Q");
            persons[3].setAge(69);

            System.out.println("Natural Order");
            for (int i = 0; i < 4; i++) {
              Person person = persons[i];
              String lastName = person.getLastName();
              String firstName = person.getFirstName();
              int age = person.getAge();
              System.out.println(lastName + ", " + firstName + ". Age:" + age);
            }
            Arrays.sort(persons, new LastNameComparator());
            System.out.println();
            System.out.println("Sorted by last name");
            for (int i = 0; i < 4; i++) {
              Person person = persons[i];
              String lastName = person.getLastName();
              String firstName = person.getFirstName();
              int age = person.getAge();
              System.out.println(lastName + ", " + firstName + ". Age:" + age);
            }
            Arrays.sort(persons, new FirstNameComparator());
            System.out.println();
            System.out.println("Sorted by first name");
            for (int i = 0; i < 4; i++) {
              Person person = persons[i];
              String lastName = person.getLastName();
              String firstName = person.getFirstName();
              int age = person.getAge();
              System.out.println(lastName + ", " + firstName + ". Age:" + age);
            }
            Arrays.sort(persons);
            System.out.println();
            System.out.println("Sorted by age");
            for (int i = 0; i < 4; i++) {
              Person person = persons[i];
              String lastName = person.getLastName();
              String firstName = person.getFirstName();
              int age = person.getAge();
              System.out.println(lastName + ", " + firstName + ". Age:" + age);
            }
        }
}

 

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