1.8新特性--Comparator

一、普通排序：

1   @Test
2     public void testComparator() {
3         List<Integer> list = Arrays.asList(1, 9, 3, 5, 0, 8);
4         list.sort(Comparator.naturalOrder());
5         System.out.println("升序：" + list);
6 
7         list.sort(Comparator.reverseOrder());
8         System.out.println("降序：" + list);
9     }

结果为：

升序：[0, 1, 3, 5, 8, 9]
降序：[9, 8, 5, 3, 1, 0]

二、根据对象属性排序：

1.根据属性排序

 1     public void testComparator() {
 2         List<Person> personList = new ArrayList<>();
 3         personList.add(new Person("Tom", 2));
 4         personList.add(new Person("Jerry", 4));
 5         personList.add(new Person("Lucy", 7));
 6         personList.add(new Person("Lily", 7));
 7 
 8         // 年龄升序
 9         personList.sort(Comparator.comparing(Person::getAge));
10         System.out.println("年龄升序:" + personList);
11 
12         // 年龄降序
13         personList.sort(Comparator.comparing(Person::getAge).reversed());
14         System.out.println("年龄降序:" + personList);
15 
16         // 先年龄降序再名字升序
17         personList.sort(Comparator.comparing(Person::getAge).reversed().thenComparing(Person::getName));
18         System.out.println("先年龄降序再名字升序:" + personList);
19     }

 

person对象：

 1 public class Person {
 2     private String name;
 3     private Integer age;
 4 
 5     public Person(String name, Integer age) {
 6         this.name = name;
 7         this.age = age;
 8     }
 9 
10     public Integer getAge() {
11         return age;
12     }
13 
14     @Override
15     public String toString() {
16         return "Person [name=" + name + ", age=" + age + "]";
17     }
18 }
View Code

结果为：

年龄升序:[Person [name=Tom, age=2], Person [name=Jerry, age=4], Person [name=Lucy, age=7], Person [name=Lily, age=7]]
年龄降序:[Person [name=Lucy, age=7], Person [name=Lily, age=7], Person [name=Jerry, age=4], Person [name=Tom, age=2]]
先年龄降序再名字升序:[Person [name=Lily, age=7], Person [name=Lucy, age=7], Person [name=Jerry, age=4], Person [name=Tom, age=2]]

 2.根据属性类型排序

根据int double 。。。排序 ：即根据对象的  int double 。。。排序;

例如：

Comparator.comparingInt(Person::getAge).reversed().thenComparing(Person::getName))

3.排序对象存在null的情况：

 1    @Test
 2     public void testComparator() {
 3         List<Person> personList = new ArrayList<>();
 4         personList.add(new Person("Tom", 2));
 5         personList.add(new Person("Jerry", 4));
 6         personList.add(new Person("Lucy", 7));
 7         personList.add(new Person("Lily", 7));
 8 
 9         personList.add(null);
10         // null的排序
11         personList.sort(
12                 Comparator.nullsFirst(Comparator.comparing(Person::getAge).reversed().thenComparing(Person::getName)));
13         System.out.println("null排第一:" + personList);
14     }

 

三、比较器的常规用法：

八(三)、常用类之比较器Comparable Comparator 

posted @ 2022-01-21 09:56  啄木鸟伍迪  阅读(85)  评论(0)  编辑  收藏  举报
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