java之TreeMap ：自然排序和定制排序

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：(鍵類實作了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);
    	
    	
    	//使用釘子排序，指明比較器
    	System.out.println("使用定制排序：（從小到大排序）");
    	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：（從大到小排序）");
    	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);
    }  
}  

  //自定義比較器:實作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();//從小到大排序
	}
} 

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

//Id作為鍵的類實作Comparable接口
class Id implements Comparable<Id>
{
	//成員屬性
	private int IdNumber;
	public int getIdNumber()
	{
		return IdNumber;
	}
	//構造函數
	public Id() {
		// TODO Auto-generated constructor stub
	}
	//構造函數
	public Id(int IdNumber)
	{
		this.IdNumber=IdNumber;
	}
	//重寫toString()方法
	@Override
	public String toString() {
		return "["+this.IdNumber+"]";
	}
	//重寫equals()方法
	@Override
	public boolean equals(Object obj) 
	{
		if(obj==this)//自己和自己比較
			return true;//那就是同一個相等了
		//傳入的引用不為空，而且兩個的類型一樣
		if(obj!=null&&obj.getClass()==this.getClass())
		{
			Id idNumber2=(Id) obj;//類型轉換
			return this.IdNumber==idNumber2.IdNumber;
			//如果兩個的編号一樣，那就認為相等
		}
		return false;
	}
	//重寫hashCode()方法
	@Override
	public int hashCode() {
		return this.IdNumber*100;
	}
	
	//重寫compareTo()方法實作自然排序
	@Override
	public int compareTo(Id o) 
	{
		//return this.IdNumber-o.IdNumber;//從小到大排序：
		return o.IdNumber-this.IdNumber;//從大到小排序
	}
}