JAVA基础（TreeSet存储自定义对象比较排序）

1，TreeSet存储自定义对象

• 存储Person对象 bean类里面必须实现Comparable 方法。（implements  Comparable）

• TreeSet集合是用来对象元素进行排序的,同样他也可以保证元素的唯一

• 当compareTo方法返回0的时候集合中只有一个元素

• 当compareTo方法返回正数的时候集合会怎么存就怎么取

• 当compareTo方法返回负数的时候集合会倒序存储

 

2，代码实现

【1】图解

• 按年龄进行排序

 

 

• 树。先去拿compareTo 去比较。 负数在左面。 正数在右面。输出结果。李四，张三，赵六，王五。

 

 

public static void demo2() {

        TreeSet ts = new TreeSet<>();

        ts.add(new Person("张三", 23));

        ts.add(new Person("李四", 13));

        ts.add(new Person("周七", 13));

        ts.add(new Person("王五", 43));

        ts.add(new Person("赵六", 33));

        

        System.out.println(ts);

    }

【2】bean 类

 

public class Person implements Comparable {

    private String name;

    private int age;

    public Person() {

        super();

        

    }

    public Person(String name, int age) {

        super();

        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 String toString() {

        return "Person [name=" + name + ", age=" + age + "]";

    }

    /*@Override

    public boolean equals(Object obj) {

        System.out.println("执行了吗");

        Person p = (Person)obj;

        return this.name.equals(p.name) && this.age == p.age;

    }

    @Override

    public int hashCode() {

        final int NUM = 38;

        return name.hashCode() * NUM + age;

    }*/

    

    /*

     * 为什么是31?

     * 1,31是一个质数,质数是能被1和自己本身整除的数

     * 2,31这个数既不大也不小

     * 3,31这个数好算,2的五次方-1,2向左移动5位

     */

    @Override

    public int hashCode() {

        final int prime = 31;

        int result = 1;

        result = prime * result + age;

        result = prime * result + ((name == null) ? 0 : name.hashCode());

        return result;

    }

    @Override

    public boolean equals(Object obj) {

        if (this == obj)                        //调用的对象和传入的对象是同一个对象

            return true;                        //直接返回true

        if (obj == null)                        //传入的对象为null

            return false;                        //返回false

        if (getClass() != obj.getClass())        //判断两个对象对应的字节码文件是否是同一个字节码

            return false;                        //如果不是直接返回false

        Person other = (Person) obj;            //向下转型

        if (age != other.age)                    //调用对象的年龄不等于传入对象的年龄

            return false;                        //返回false

        if (name == null) {                        //调用对象的姓名为null

            if (other.name != null)                //传入对象的姓名不为null

                return false;                    //返回false

        } else if (!name.equals(other.name))    //调用对象的姓名不等于传入对象的姓名

            return false;                        //返回false

        return true;                            //返回true

    }

    /*@Override

    //按照年龄排序

    public int compareTo(Person o) {

        int num = this.age - o.age;                //年龄是比较的主要条件

        return num == 0 ? this.name.compareTo(o.name) : num;//姓名是比较的次要条件

    }*/

    /*@Override

    //按照姓名排序

    public int compareTo(Person o) {

        int num = this.name.compareTo(o.name);        //姓名是主要条件

        return num == 0 ? this.age - o.age : num;    //年龄是次要条件

    }*/

    /*

     * aaa

     * bbb

     */

    public int compareTo(Person o) {

        int length = this.name.length() - o.name.length();                //比较长度为主要条件

        int num = length == 0 ? this.name.compareTo(o.name) : length;    //比较内容为次要条件

        return num == 0 ? this.age - o.age : num;                        //比较年龄为次要条件

    }

    

}