Java TreeMap: Natural sorting and custom sorting

import java.util.Comparator;
import java.util.TreeMap;
 
public class Test {
    
      
    public static void main(String[] args) 
    {
    
      
    	System.out.println("使用自然排序：(键类实现了compareTo接口)");
    	TreeMap<Id, String> treeMap=new TreeMap<Id,String>();
    	treeMap.put(new Id(1000), "demo1");
    	treeMap.put(new Id(1001), "demo2");
    	treeMap.put(new Id(1002), "demo3");
    	treeMap.put(new Id(1003), "demo4");
    	treeMap.put(new Id(1004), "demo5");
    	System.out.println("treeMap="+treeMap);
    	
    	
    	//使用钉子排序，指明比较器
    	System.out.println("使用定制排序：（从小到大排序）");
    	TreeMap<Id, String> treeMap2=
    			new TreeMap<Id,String>(new MyComparatorBigToSmall());
    	treeMap2.put(new Id(1000), "demo1");
    	treeMap2.put(new Id(1001), "demo2");
    	treeMap2.put(new Id(1002), "demo3");
    	treeMap2.put(new Id(1003), "demo4");
    	treeMap2.put(new Id(1004), "demo5");
    	System.out.println("treeMap2="+treeMap2);
    	
    	System.out.println("使用定制排序：（从大到小排序）");
    	TreeMap<Id, String> treeMap3=
    			new TreeMap<Id,String>(new MyComparatorSmallToBig());
    	treeMap3.put(new Id(1000), "demo1");
    	treeMap3.put(new Id(1001), "demo2");
    	treeMap3.put(new Id(1002), "demo3");
    	treeMap3.put(new Id(1003), "demo4");
    	treeMap3.put(new Id(1004), "demo5");
    	System.out.println("treeMap3="+treeMap3);
    }  
}  

  //自定义比较器:实现comparator接口
class MyComparatorBigToSmall implements Comparator<Id> //使用泛型
{
    
      
	@Override
	public int compare(Id o1, Id o2) {
    
    
		return o1.getIdNumber()-o2.getIdNumber();//从小到大排序
	}
} 

class MyComparatorSmallToBig implements Comparator<Id>
{
    
    
	@Override
	public int compare(Id o1, Id o2) {
    
    
		return o2.getIdNumber()-o1.getIdNumber();//从大到小排序
	}
}

//Id作为键的类实现Comparable接口
class Id implements Comparable<Id>
{
    
    
	//成员属性
	private int IdNumber;
	public int getIdNumber()
	{
    
    
		return IdNumber;
	}
	//构造函数
	public Id() {
    
    
		// TODO Auto-generated constructor stub
	}
	//构造函数
	public Id(int IdNumber)
	{
    
    
		this.IdNumber=IdNumber;
	}
	//重写toString()方法
	@Override
	public String toString() {
    
    
		return "["+this.IdNumber+"]";
	}
	//重写equals()方法
	@Override
	public boolean equals(Object obj) 
	{
    
    
		if(obj==this)//自己和自己比较
			return true;//那就是同一个相等了
		//传入的引用不为空，而且两个的类型一样
		if(obj!=null&&obj.getClass()==this.getClass())
		{
    
    
			Id idNumber2=(Id) obj;//类型转换
			return this.IdNumber==idNumber2.IdNumber;
			//如果两个的编号一样，那就认为相等
		}
		return false;
	}
	//重写hashCode()方法
	@Override
	public int hashCode() {
    
    
		return this.IdNumber*100;
	}
	
	//重写compareTo()方法实现自然排序
	@Override
	public int compareTo(Id o) 
	{
    
    
		//return this.IdNumber-o.IdNumber;//从小到大排序：
		return o.IdNumber-this.IdNumber;//从大到小排序
	}
}