Jdk8新特性之排序

Comparator提供的方法

/**
 * @author WGR
 * @create 2020/4/13 -- 16:12
 */
public class Person {

    private String name;
    private Integer age;
    private Double salary;


    public Person(String name, Integer age, Double salary) {
        super();
        this.name = name;
        this.age = age;
        this.salary = salary;
    }

    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 Double getSalary() {
        return salary;
    }
    public void setSalary(Double salary) {
        this.salary = salary;
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + ", salary=" + salary + "]";
    }


}

 排序实现

/**
 * @author WGR
 * @create 2020/4/13 -- 16:14
 */
public class _Comparator {
    List<Person> personList = new ArrayList<>();

    @Before
    public  void before() {
        personList.add(new Person("hepengju", 28, 20000.0));
        personList.add(new Person("lisi", 44, 40000.0));
        personList.add(new Person("wangwu", 55, 50000.0));
        personList.add(new Person("zhaoliu", 66, 60000.0));
        personList.add(new Person("zhangsan", 33, 33333.0));
        personList.add(new Person("zhangsan", 23, 30000.0));
    }

    //按照名字排序
    @Test
    public  void test() {
        personList.stream().sorted(Comparator.comparing(Person::getName)).forEach(System.out::println);
//        Person [name=hepengju, age=28, salary=20000.0]
//        Person [name=lisi, age=44, salary=40000.0]
//        Person [name=wangwu, age=55, salary=50000.0]
//        Person [name=zhangsan, age=33, salary=33333.0]
//        Person [name=zhangsan, age=23, salary=30000.0]
//        Person [name=zhaoliu, age=66, salary=60000.0]
    }

    //按照名字排序降序
    @Test
    public  void test4() {
        personList.stream().sorted(Comparator.comparing(Person::getName).reversed()).forEach(System.out::println);
//        Person [name=zhaoliu, age=66, salary=60000.0]
//        Person [name=zhangsan, age=33, salary=33333.0]
//        Person [name=zhangsan, age=23, salary=30000.0]
//        Person [name=wangwu, age=55, salary=50000.0]
//        Person [name=lisi, age=44, salary=40000.0]
//        Person [name=hepengju, age=28, salary=20000.0]
    }

    // 先按照名字排序, 名字一样再按照年龄排序, 年龄一样再按照薪资排序
    @Test
    public void test2(){
        personList.stream().sorted(Comparator.comparing(Person::getName).thenComparing(Person::getAge).thenComparing(Person::getSalary)).forEach(System.out::println);
//        Person [name=hepengju, age=28, salary=20000.0]
//        Person [name=lisi, age=44, salary=40000.0]
//        Person [name=wangwu, age=55, salary=50000.0]
//        Person [name=zhangsan, age=23, salary=30000.0]
//        Person [name=zhangsan, age=33, salary=33333.0]
//        Person [name=zhaoliu, age=66, salary=60000.0]
    }

    // 4. 处理所有空值问题(null都到最后)
    @Test
    public void test3(){
       // personList.add(null);
        personList.add(new Person(null, 33, 30000.0));
        personList.add(new Person("zhangsan", null, 30000.0));
        personList.add(new Person("zhangsan", 33, null));
        personList.add(new Person(null, null, null));
        personList.stream().sorted(Comparator.comparing(Person::getName,Comparator.nullsLast(Comparator.naturalOrder()))
                .thenComparing(Person::getName,Comparator.nullsLast(Comparator.naturalOrder()))
                .thenComparing(Person::getName,Comparator.nullsLast(Comparator.naturalOrder()))
                ).forEach(System.out::println);
//        Person [name=hepengju, age=28, salary=20000.0]
//        Person [name=lisi, age=44, salary=40000.0]
//        Person [name=wangwu, age=55, salary=50000.0]
//        Person [name=zhangsan, age=33, salary=33333.0]
//        Person [name=zhangsan, age=23, salary=30000.0]
//        Person [name=zhangsan, age=null, salary=30000.0]
//        Person [name=zhangsan, age=33, salary=null]
//        Person [name=zhaoliu, age=66, salary=60000.0]
//        Person [name=null, age=33, salary=30000.0]
//        Person [name=null, age=null, salary=null]

    }

   //jdk8 lambda排序
    @Test
    public  void test5() {
        personList.stream().sorted((p1,p2) -> p1.getName().compareTo(p2.getName()) ).forEach(System.out::println);
//        Person [name=hepengju, age=28, salary=20000.0]
//        Person [name=lisi, age=44, salary=40000.0]
//        Person [name=wangwu, age=55, salary=50000.0]
//        Person [name=zhangsan, age=33, salary=33333.0]
//        Person [name=zhangsan, age=23, salary=30000.0]
//        Person [name=zhaoliu, age=66, salary=60000.0]
    }

    @Test
    public  void test6() {
        personList.stream().sorted((p1,p2) -> p1.getAge() - p2.getAge() ).forEach(System.out::println);
//        Person [name=zhangsan, age=23, salary=30000.0]
//        Person [name=hepengju, age=28, salary=20000.0]
//        Person [name=zhangsan, age=33, salary=33333.0]
//        Person [name=lisi, age=44, salary=40000.0]
//        Person [name=wangwu, age=55, salary=50000.0]
//        Person [name=zhaoliu, age=66, salary=60000.0]
    }

}