SortedSet custom sorting and sortedset custom sorting

SortedSet custom sorting and sortedset custom sorting

We know that a Set can store a series of objects, such as int and class, which are unordered and repeatable. Today we will discuss:Can the Set be sorted? How can I customize the sorting rules?

First, steal a graph to describe the inheritance relationship of the Set:

We will discuss the usage of SortedSet today.
(Note: it is an excuse to use their implementation classes)

Next we will sort SortedSet:

public class test {    public static void main(String[] args) {        TreeSet<String> set=new TreeSet<String>();        set.add("B");        set.add("D");        set.add("A");        set.add("E");        set.add("C");        System.out.println(set);    }}

What is the result? [A, B, C, D, E]...
It is arranged in alphabetical order, so if I want to arrange it in reverse order, I need to customize a sorting rule here.

// A construction method of the TreeSet // comparator: This is the custom sorting Rule public TreeSet (Comparator <? Super E> comparator) {this (new TreeMap <> (comparator ));}

Let's test it;

Public class test {public static void main (String [] args) {// a new custom Comparator TreeSet <String> set = new TreeSet <String> (new MyComparator ()); set. add ("B"); set. add ("D"); set. add ("A"); set. add ("E"); set. add ("C"); System. out. println (set) ;}} class MyComparator implements Comparator {@ Override public int compare (Object o1, Object o2) {String s1 = (String) o1; String s2 = (String) o2; // reverse return s2.compareTo (s1 );}}

Result and clear: [E, D, C, B, A]

This is very simple. If we use a custom class, such as a Person class, we need to sort by age. Let's take a look at how to implement it:

Public class test {public static void main (String [] args) {// custom sorting rule TreeSet <Person> set = new TreeSet <Person> (new MyComparator ()); set. add (new Person ("A", 20); set. add (new Person ("D", 10); set. add (new Person ("E", 40); set. add (new Person ("C", 50); set. add (new Person ("B", 30); System. out. println (set) ;}} class Person {String name; int age; public Person (String name, int age) {this. name = name; this. age = age ;}@ Override // rewrite the toString method to specify the output format: public String toString () {return "name:" + name + ", age = "+ age ;}} class MyComparator implements Comparator {@ Override public int compare (Object o1, Object o2) {Person p1 = (Person) o1; Person p2 = (Person) o2; // custom comparison rule return (int) (p1.age-p2.age );}}

Result:
[Name: D, age = 10, name: A, age = 20, name: B, age = 30, name: E, age = 40, name: C, age = 50]

Achieve the desired result.

In this way, we can sort the Set.