java中Map如何根据key的大小进行排序详解

import java.util.Iterator;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import java.util.TreeMap;
public class Main {
	public static void main(String args[]) {		
		System.out.println("kaishi");
		Random random = new Random();
		Map<Double, Integer> map = new TreeMap<Double, Integer>();
		//随机产生数据，存入到map中；默认情况下时升序的。
		for(int i=0;i<100;i++) {
			map.put(random.nextDouble()*1000,random.nextInt(1000));
		}		
		//使用Iterator来取key-value对；
		Set<Double> keySet = map.keySet();
	    Iterator<Double> iter = keySet.iterator();
	    while (iter.hasNext()) {
	        Double key = iter.next();
	        System.out.println(key + ":" + map.get(key));  //打印结果，会发现key都是按升序输出的
	        }
	}
}

import java.util.Iterator;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import java.util.TreeMap;
import java.util.Comparator;
public class Main {
	public static void main(String args[]) {		
		System.out.println("kaishi");
		Random random = new Random();
		Map<Double, Integer> map = new TreeMap<Double, Integer>(
				new Comparator<Double>(){
        			@Override
        			public int compare(Double o1, Double o2) {
        				//利用Comparator来实现降序；
        				return (int) (o2-o1);
        			}
           });
		for(int i=0;i<100;i++) {
			map.put(random.nextDouble()*1000,random.nextInt(1000));
		}		
		Set<Double> keySet = map.keySet();
	    Iterator<Double> iter = keySet.iterator();
	    while (iter.hasNext()) {
	        Double key = iter.next();
	        System.out.println(key + ":" + map.get(key));//打印结果，会发现key都是按降序输出的
	        }
	}
}