TreeSetTest

简介

java 核心编程

关于TreeSetTest的知识

输出

[[descrition=Toaster,partNumber=1234], [descrition=Widget,partNumber=4562], [descrition=Modem,partNumber=9912]]
[[descrition=Modem,partNumber=9912], [descrition=Toaster,partNumber=1234], [descrition=Widget,partNumber=4562]]

有两个输出，第一个是默认自带的比较函数结构

    public int compareTo(Item other){
        int diff = Integer.compare(partNumber, other.partNumber); // 先比较编号再比较字符串
        return diff != 0? diff : description.compareTo(other.description);
    }

表示 先比较编号再比较字符串

第二个输出，设定的比较方式采用字符串比较的方式进行排序。

NavigableSet sortByDescription = new TreeSet<>(Comparator.comparing(Item::getDescription));

code

import java.util.*;
public class TreeSetTest {
    public static void main(String[]args){
        SortedSet<Item> parts = new TreeSet<>();
        parts.add(new Item("Toaster", 1234));
        parts.add(new Item("Widget", 4562));
        parts.add(new Item("Modem", 9912));
        System.out.println(parts);

        NavigableSet<Item> sortByDescription = new TreeSet<>(Comparator.comparing(Item::getDescription)); // 设定的比较方式，直接通过字符串进行排序

        sortByDescription.addAll(parts);
        System.out.println(sortByDescription);
    }
}

import java.util.*;
public class Item implements Comparable<Item>{
    private String description;
    private int partNumber;
    /**
     * Constructs an item.
     *
     * @param aDescription
     *          the item's description
     * @param aPartNumber
     *          the item's part number
     */
    public Item(String aDescription, int aPartNumber){
        description = aDescription;
        partNumber = aPartNumber;
    }

    public String getDescription(){
        return description;
    }

    public String toString(){
        return "[descrition=" + description + ",partNumber=" + partNumber + "]";
    }

    public boolean equals(Object otherObject){
        if(this == otherObject) return true;
        if (otherObject == null) return false;
        if(getClass() != otherObject.getClass()) return false;
        Item other = (Item) otherObject;
        return Objects.equals(description,other.description) && partNumber == other.partNumber;
    }

    public int hashCode(){
        return Objects.hash(description, partNumber);
    }

    public int compareTo(Item other){
        int diff = Integer.compare(partNumber, other.partNumber); // 先比较编号再比较字符串
        return diff != 0? diff : description.compareTo(other.description);
    }
}