TreeSet的运用之使用内部比较器实现自定义有序（重要）

Student.java

package com.sxt.set3;
/*
 * TreeSet：有序
 * implements Comparable<Student>
 * 如果用内部比较器TreeSet必须是实现Comparable接口来实现有序 否则会出现报错：com.sxt.set4.Student cannot be cast to java.lang.Comparable
 * 使用泛型是为了在重写compareTo()方式时，object不用强制转换类型
 */
//内部比较器：在类内重写比较规则即compareTo()方法
public class Student implements Comparable<Student> {
    private String name;
    private int age;
    private double salary;
    public Student(String name, int age, double salary) {
        super();
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
    public Student() {
        super();
    }
    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;
    }
    public double getSalary() {
        return salary;
    }
    public void setSalary(double salary) {
        this.salary = salary;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + ", salary=" + salary + "]";
    }
    //内部比较器之排序规则 按年龄
    @Override
    public int compareTo(Student o) {

        return this.age - o.age;
    }

}

TestStudent.java

package com.sxt.set3;
/*
 * TreeSet
 */
import java.util.Set;
import java.util.TreeSet;

public class TestStudent {
    public static void main(String[] args) {
        Set<Student> arr = new TreeSet<>();
        arr.add(new Student("bbb", 21, 532.2));
        arr.add(new Student("ccc", 32, 32.2));
        arr.add(new Student("ddd", 11, 352.2));
        arr.add(new Student("aaa", 15, 32.2));
        //遍历
        for(Student s:arr){
            System.out.println(s);
        }
//        按照内部比较器按年龄排序结果：
//        Student [name=ddd, age=11, salary=352.2]
//        Student [name=aaa, age=15, salary=32.2]
//        Student [name=bbb, age=21, salary=532.2]
//        Student [name=ccc, age=32, salary=32.2]

    }
}