Comparable接口的使用

1、当数据需要排序时，我们可以用这个接口进行排序。
2、代码样例

public class Student implements Comparable<Student>{
    private int id;
    private  String name;
    private  int age;

    public Student() {
    }

    public Student(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @Override
    public int compareTo(Student o) {
        System.out.println("调用方法");
        if(this.id<o.id){
            return -1;
        }else if (this.id>o.id){
            return 1;
        }else {
            if (this.age<o.age){
                return -1;
            }else if (this.age<o.age){
                return 1;
            }else return 0;
        }

    }
}
public class Test03 {
    public static void main(String[] args) {
        List<Student> students=new ArrayList<>();
        Student s1=new Student(1,"刘德华",18);
        Student s2=new Student(1,"张学友",20);
        Student s3=new Student(2,"郭富城",25);
        Student s4=new Student(3,"黎明",25);
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
        for (Student s:students){
            System.out.println(s.toString());
        }
        Collections.sort(students);//自动调用compareTo
        for (Student s:students){
            System.out.println(s.toString());
        }


    }
}

3、代码输出结果

Student{id=1, name='刘德华', age=18}
Student{id=1, name='张学友', age=20}
Student{id=2, name='郭富城', age=25}
Student{id=3, name='黎明', age=25}
调用方法
调用方法
调用方法
Student{id=1, name='刘德华', age=18}
Student{id=1, name='张学友', age=20}
Student{id=2, name='郭富城', age=25}
Student{id=3, name='黎明', age=25}

4、代码解释
在集合Collection和Arrays类中，都有sort()方法，可以对于集合和数组进行排序，sort方法实现了Comparable的接口，调用了自然方法。我们可以再student类里实现Comparable接口，重写他的排序方法，sort会自动调用，实现排序的功能。