比较器Comparable与Comparator实践-蒲公英云

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}]