java集合TreeMap使用自然排序，定制排序

import java.util.Comparator;
import java.util.TreeMap;

public class Demo3 {
public static void main(String[] args)
{
System.out.println("使用自然排序：");
TreeMap<IdNumber2, String> treeMap=new TreeMap<IdNumber2,String>();
treeMap.put(new IdNumber2(1000), "王尼玛");
treeMap.put(new IdNumber2(1001), "万尼玛");
treeMap.put(new IdNumber2(1002), "蓝尼玛");
treeMap.put(new IdNumber2(1003), "冯尼玛");
treeMap.put(new IdNumber2(1004), "秦尼玛");
System.out.println("treeMap="+treeMap);
System.out.println("使用定制排序：（从小到大排序）");
//使用钉子排序，指明比较器
TreeMap<IdNumber2, String> treeMap2=
new TreeMap<IdNumber2,String>(new MyComparatorBigToSmall());
treeMap2.put(new IdNumber2(1000), "王尼玛");
treeMap2.put(new IdNumber2(1001), "万尼玛");
treeMap2.put(new IdNumber2(1002), "蓝尼玛");
treeMap2.put(new IdNumber2(1003), "冯尼玛");
treeMap2.put(new IdNumber2(1004), "秦尼玛");
System.out.println("treeMap2="+treeMap2);
System.out.println("使用定制排序：（从大到小排序）");
TreeMap<IdNumber2, String> treeMap3=
new TreeMap<IdNumber2,String>(new MyComparatorSmallToBig());
treeMap3.put(new IdNumber2(1000), "王尼玛");
treeMap3.put(new IdNumber2(1001), "万尼玛");
treeMap3.put(new IdNumber2(1002), "蓝尼玛");
treeMap3.put(new IdNumber2(1003), "冯尼玛");
treeMap3.put(new IdNumber2(1004), "秦尼玛");
System.out.println("treeMap3="+treeMap3);
}
}
//自定义比较器:实现comparator接口
class MyComparatorBigToSmall implements Comparator<IdNumber2> //使用泛型
{

@Override
public int compare(IdNumber2 o1, IdNumber2 o2) {
// TODO Auto-generated method stub
return o1.getIdNumber()-o2.getIdNumber();//从小到大排序
}
}
class MyComparatorSmallToBig implements Comparator<IdNumber2>
{
@Override
public int compare(IdNumber2 o1, IdNumber2 o2) {
// TODO Auto-generated method stub
return o2.getIdNumber()-o1.getIdNumber();//从小到大排序
}
}
//z作为键的类实现Comparable接口
class IdNumber2 implements Comparable<IdNumber2>
{
//成员属性
private int IdNumber;
public int getIdNumber()
{
return IdNumber;
}
//构造函数
public IdNumber2() {
// TODO Auto-generated constructor stub
}
//构造函数
public IdNumber2(int IdNumber)
{
this.IdNumber=IdNumber;
}
//重写toString()方法
@Override
public String toString() {
// TODO Auto-generated method stub
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())
{
IdNumber2 idNumber2=(IdNumber2) 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() {
// TODO Auto-generated method stub
return this.IdNumber*100;
}
//重写compareTo()方法实现自然排序
@Override
public int compareTo(IdNumber2 o)
{
// TODO Auto-generated method stub
//return this.IdNumber-o.IdNumber;//从小到大排序：
return o.IdNumber-this.IdNumber;//从大到小排序
}
}

结果：

使用自然排序：treeMap={[1004]=秦尼玛, [1003]=冯尼玛, [1002]=蓝尼玛, [1001]=万尼玛, [1000]=王尼玛}使用定制排序：（从小到大排序）treeMap2={[1000]=王尼玛, [1001]=万尼玛, [1002]=蓝尼玛, [1003]=冯尼玛, [1004]=秦尼玛}使用定制排序：（从大到小排序）treeMap3={[1004]=秦尼玛, [1003]=冯尼玛, [1002]=蓝尼玛, [1001]=万尼玛, [1000]=王尼玛}