HashMap 和TreeMap的比较
HashMap 和TreeMap的比较
与Java相关信息
HashMap的代码为：

import java.util.*; public class hashmap {     Map calendar = new HashMap();     public hashmap(String d[],String i[]){         for(int j=0;j<d.length;j++){             calendar.put(d[j], i[j]);         }     }     public static void main(String[] args) {         String [] dates = {"10/4","05/7","12/7","01/5"};         String [] items = {"Z","Y","X","C"};         hashmap example = new hashmap(dates,items);         Set mapping = example.calendar.entrySet();         System.out.println("map= "+example.calendar);         System.out.println("Object\tkey\tvalue");         for(Iterator it = mapping.iterator();it.hasNext();){             Map.Entry me = (Map.Entry)it.next();             Object ok = me.getKey();             Object ov = me.getValue();             System.out.print(me+"\t");             System.out.print(ok+"\t");             System.out.println(ov);         }     } } 

HashTree的代码：

import java.util.*; public class hashmap {     Map calendar = new TreeMap();     public hashmap(String d[],String i[]){         for(int j=0;j<d.length;j++){             calendar.put(d[j], i[j]);         }     }     public static void main(String[] args) {         String [] dates = {"10/4","05/7","12/7","01/5"};         String [] items = {"Z","Y","X","C"};         hashmap example = new hashmap(dates,items);         Set mapping = example.calendar.entrySet();         System.out.println("map= "+example.calendar);         System.out.println("Object\tkey\tvalue");         for(Iterator it = mapping.iterator();it.hasNext();){             Map.Entry me = (Map.Entry)it.next();             Object ok = me.getKey();             Object ov = me.getValue();             System.out.print(me+"\t");             System.out.print(ok+"\t");             System.out.println(ov);         }     } }

代码大致相同，但是HashMap的输出是无序的，TreeMap的输出是按关键字升序排列的！


但是TreeMap的开销也比较HashMap大，因为它要处理排序！