Java 中的 compareTo() 和 compare() 方法有什么区别?\

javaobject oriented programmingprogramming更新于 2025/5/22 6:36:17

Comparable 接口提供了 compareTo() 方法用于对对象进行排序。此排序称为类的自然排序，而 compareTo() 方法称为其 自然比较方法。Comparator 接口提供了执行 排序操作 的方法。通过使用 Comparator 接口，我们可以执行 多个排序序列。我们可以根据多个数据成员对对象进行排序。

compareTo()

compareTo() 方法将此对象与 o1 对象进行比较，并返回一个整数。

语法

public int compareTo(Object o1)

仅当此对象小于 o1 时，它才返回 –ve 数字。
仅当此对象大于 o1 时，它才返回 +ve 数字。
仅当此对象等于 o1 时，它才返回 0。

示例

import java.util.*;
class Employee implements Comparable {
   String name;
   int age;
   Employee(String name, int age) {
      this.name = name;
      this.age = age;
   }
   //重写 compareTo 方法
   @Override
   public int compareTo(Object o) {
      return this.age - ((Employee) o).age;
   }
}
public class ComparableDemo {
   public static void main(String[] args) {
      // CREATION
      List list = new ArrayList<>();
      //INSERTION
      list.add(new Employee("Krishna", 30));
      list.add(new Employee("Archana", 28));
      list.add(new Employee("Vineet", 25));
      list.add(new Employee("Ramesh", 38));
      list.add(new Employee("Alok", 28));
      System.out.println("Before sorting: ");
      for (Employee e : list) {
         System.out.print("[ EMP : age = " + e.age + " ] ");
      }
      //SORTING
      Collections.sort(list);
      System.out.println("After sorting: ");
      for (Employee e : list) {
         System.out.print("[ EMP : age = " + e.age + " ] ");
      }
   }
}

输出

Before sorting:
[ EMP : age = 2 ] [ EMP : age = 33 ] [ EMP : age = 11 ] [ EMP : age = 34 ] [ EMP : age = 7 ]
After sorting:
[ EMP : age = 2 ] [ EMP : age = 7 ] [ EMP : age = 11 ] [ EMP : age = 33 ] [ EMP : age = 34 ]

compare()

compare() 方法将第一个对象与第二个对象进行比较，并返回一个整数

语法

public int compare (Object o1,Object o2)

如果 & 仅当 o1 小于 o2 时，它返回 –ve 数字
如果 & 仅当 o1 大于 o2 时，它返回 +ve 数字
如果 & 仅当 o1 等于 o2 时，它返回 0

示例

import java.util.*;
class Student {
   String name;
   int age, roll;
   Student(String name, int age, int roll) {
      this.name = name;
      this.age = age;
      this.roll = roll;
   }
}
class AgeComparator implements Comparator {
   @Override
   public int compare(Object o1, Object o2) {
      return ((Student) o1).age - ((Student) o2).age;
   }
}
class RollComparator implements Comparator {
   @Override
   public int compare(Object o1, Object o2) {
      return ((Student) o1).roll - ((Student) o2).roll;
   }
}
public class ComparatorDemo {
   public static void main(String[] args) {
      List list = new ArrayList<>();
      list.add(new Student("Ramesh", 30, 20));
      list.add(new Student("Adithya", 7, 10));
      list.add(new Student("Krishna", 25, 5));
      list.add(new Student("Vineet", 24, 15));
      System.out.println("BEFORE SORTING");
      for (Student e : list) {
         System.out.println("[ STU : name = " + e.name + " age = " + e.age + " roll = " + e.roll + "]");
      }
      Collections.sort(list,new AgeComparator());
      System.out.println("AFTER SORTING WITH AGE");
      for (Student e : list) {
         System.out.println("[ STU : name = " + e.name + " age = " + e.age + " ]");
      }
      Collections.sort(list,new RollComparator());
      System.out.println("AFTER SORTING WITH ROLL");
      for (Student e : list) {
         System.out.println("[ STU : name = " + e.name + " roll = " + e.roll + " ]");
      }
   }
}

输出

BEFORE SORTING
[ STU : name = Ramesh age = 30 roll = 20 ]
[ STU : name = Adithya age = 7 roll = 10 ]
[ STU : name = Krishna age = 25 roll = 5 ]
[ STU : name = Vineet age = 24 roll = 15 ]
AFTER SORTING WITH AGE
[ STU : name = Adithya age = 7 ]
[ STU : name = Vineet age = 24 ]
[ STU : name = Krishna age = 25 ]
[ STU : name = Ramesh age = 30 ]
AFTER SORTING WITH ROLL
[ STU : name = Krishna roll = 5 ]
[ STU : name = Adithya roll = 10 ]
[ STU : name = Vineet roll = 15 ]
[ STU : name = Ramesh roll = 20 ]