Java学习之路---集合练习：TreeSet集合，存储学生类，并按照年龄大小顺序排序，若年龄相同，则按照姓名顺序

public class Student {
    private String name;
    private int age;

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

    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;
    }
}

import java.util.TreeSet;

public class TreeSetTest {
    public static void main(String[] args) {
        TreeSet ts = new TreeSet<>();
        Student s1 = new Student("张三", 16);
        Student s2 = new Student("李四", 16);
        Student s3 = new Student("张三", 16);
        ts.add(s1);
        ts.add(s2);
        ts.add(s3);
        for (Student s : ts)
            System.out.println(s.getName() + "," + s.getAge());
    }
}

可以发现控制台报错：

其原因是若使用自然排序，需要学生类实现Comparable接口并重写compareTo方法：
重写后要修改方法的排序规则，不过不修改，只会添加第一个元素
修改后的代码：

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

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

    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 int compareTo(Student o) {
        //判断年龄大小
        int num = this.age - o.getAge();
        //判断首字母
        int num2 = num == 0 ? this.name.compareTo(o.name) : num;
        return num2;
    }
}

import java.util.TreeSet;

public class TreeSetTest {
    public static void main(String[] args) {
        TreeSet ts = new TreeSet<>();
        Student s1 = new Student("张三", 16);
        Student s2 = new Student("李四", 33);
        Student s3 = new Student("王五", 25);
        Student s4 = new Student("王五", 25);
        Student s5 = new Student("赵六", 25);
        ts.add(s1);
        ts.add(s2);
        ts.add(s3);
        ts.add(s4);
        ts.add(s5);
        for (Student s : ts)
            System.out.println(s.getName() + "," + s.getAge());
    }
}

可以看到，输出结果为，有序不重复，且年龄重复按照首字母排序