Comparable和Comparator的区别

谁借莪１个温暖的怀抱￠ 2021-12-13 14:59 345阅读 0赞

Comparable和Comparator都是用于比较数据大小的，Comparable位于java.lang包下，实现该接口需要重写compareTo方法；Comparator位于java.util包下，实现该接口需要重写compare方法。

## Comparable接口只有一个方法： ##

public int compareTo(T o);

调用此方法的对象，也就是this和o进行比较，若返回值大于0，则this大于o;返回值等于0则this等于o；返回值小于0则this小于o。因为this是需要一个明确的比较对象的，也就是一般情况下我们会在定义User类的时候有排序的需求，所以我们定义的类需要实现此接口。

package com.dalingjia.bean;
    
    import java.util.*;
    
    public class Student implements Comparable<Student> {
    
        private String name;
        private Integer age;
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        public Student(String name, Integer age) {
            this.name = name;
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        @Override
        public int compareTo(Student o) {
            //先比较name，name相同在比较age
            if(this.name.compareTo(o.name) == 0){
                if(this.age.compareTo(o.age) == 0){
                    return 0;
                }else if (this.age > o.age){
                    return 1;
                }else {
                    return -1;
                }
            }else if(this.name.compareTo(o.name) > 0){
                return 1;
            }else {
                return -1;
            }
        }
    
        public static void main(String[] args) {
            List list = new ArrayList<Student>();
            list.add(new Student("gol",21));
            list.add(new Student("gol",19));
            list.add(new Student("xiao",21));
            list.add(new Student("long",21));
            System.out.println("排序前："+list);
            //排序规则：先按name排序，若name相等则再比较age
            Collections.sort(list);
            System.out.println("排序后："+list);
        }
    }

打印结果：

排序前：[Student{name='gol', age=21}, Student{name='gol', age=19}, Student{name='xiao', age=21}, Student{name='long', age=21}]
    排序后：[Student{name='gol', age=19}, Student{name='gol', age=21}, Student{name='long', age=21}, Student{name='xiao', age=21}]

## Comparator接口有一个重要的方法： ##

int compare(T o1, T o2);

compare比较的o1和o2，返回值大于0则o1大于o2，依次类推。

package com.dalingjia.bean;
    
    import java.util.*;
    
    public class Student {
        private String name;
        private Integer age;
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        public Student(String name, Integer age) {
            this.name = name;
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        static class StudentComparator implements Comparator<Student> {
            @Override
            public int compare(Student o1, Student o2) {
                if (o1.name.compareTo(o2.name) == 0) {
                    if (o1.age == o2.age) {
                        return 0;
                    } else if (o1.age > o2.age) {
                        return 1;
                    } else {
                        return -1;
                    }
                } else if (o1.name.compareTo(o2.name) > 0) {
                    return 1;
                } else {
                    return -1;
                }
            }
        }
    
        public static void main(String[] args) {
            List list = new ArrayList<Student>();
            list.add(new Student("gol", 21));
            list.add(new Student("gol", 19));
            list.add(new Student("xiao", 21));
            list.add(new Student("long", 21));
            System.out.println("排序前：" + list);
            //排序规则：先按name排序，若name相等则再比较age
            Comparator comparator = new StudentComparator();
            Collections.sort(list, comparator);
            System.out.println("排序后：" + list);
        }
    }