比较器Comparable与Comparator实践

太过爱你忘了你带给我的痛 2022-07-14 09:56 194阅读 0赞

## 比较器Comparable与Comparator实践 ##

**Comparable**：该比较器是用于对象的内部比较，比较的是属性。它的方法：

public int compareTo(T o);

**Comparator**：该比较器用于对象的外部比较，比较的是对象，一般这个比较的对象也实现了Comparable接口。Comparator的方法有多个，但一般我们只需要实现：

int compare(T o1, T o2);

实例代码：

声明一个People类，实现Comparable接口，内部排序优先级，city>age>name>sex。

public class People implements Comparable<People> {
        public String name;
        public int sex;
        public String city;
        public int age;
    
        public People(String name, int sex, String city, int age) {
            this.name = name;
            this.sex = sex;
            this.city = city;
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "People{" +
                    "name='" + name + '\'' +
                    ", sex=" + sex +
                    ", city='" + city + '\'' +
                    ", age=" + age +
                    '}';
        }
    
        /** * 比较规则优先级：city>age>name>sex */
        @Override
        public int compareTo(People people) {
    
            int result = 0;
    
            if (people == null) return result;
    
            //比较city
            result = people.city.compareTo(city);//String实现了Comparable接口
    
            if (result == 0) {
       //city 相同
                result = people.age - age;//比较age
            }
    
            if (result == 0) {
       // age相同
                result = people.name.compareTo(name);//比较name
            }
    
            if (result == 0) { //name相同
                result = people.sex - sex;//比较sex
            }
    
            return result;
        }
    }

实现一个Comparator比较器

public class PeopleComparator implements Comparator<People> { 
        @Override
        public int compare(People people1, People people2) {
            if (people1 != null && people2 != null) {
                return people2.compareTo(people1);//后者和前者比较
            }
            return 0;
        }
    }

测试代码实现：

public class Test { 
        public static void main(String[] args) {
            List<People> list = new ArrayList<>();
    
            list.add(new People("moly", 1, "shanghai", 24));
            list.add(new People("lili", 1, "beijing", 25));
            list.add(new People("pop", 1, "shenzhen", 24));
            list.add(new People("momo", 0, "shanghai", 23
            ));
    
            System.out.println(list.toString());
    
            Collections.sort(list,new PeopleComparator());
    
            System.out.println(list.toString());
        }
    }

打印结果：

sort before:[People{name='moly', sex=1, city='shanghai', age=24}, People{name='lili', sex=1, city='beijing', age=25}, People{name='pop', sex=1, city='shenzhen', age=24}, People{name='momo', sex=0, city='shanghai', age=23}]
    
    sort after:[People{name='lili', sex=1, city='beijing', age=25}, People{name='momo', sex=0, city='shanghai', age=23}, People{name='moly', sex=1, city='shanghai', age=24}, People{name='pop', sex=1, city='shenzhen', age=24}]