学步园

1. Method invokes inefficient Number constructor; use static valueOf instead

Long buyerPickupAddressId = new Long(84); -> Long buyerPickupAddressId = Long.valueOf(84);

2. Method concatenates strings using + in a loop

Suggest: use StringBuffer

3. Inefficient use of keySet iterator instead of entrySet iterator

package com.cathy.mywebtest.common;

import java.util.Calendar; 
import java.util.Date; 
import java.util.HashMap; 
import java.util.Iterator; 
import java.util.Map.Entry; 
 
/**
 * 测试keySet()与entrySet()的迭代时间
 * keySet():迭代后只能通过get()取key
 * entrySet()：迭代后可以e.getKey()，e.getValue()取key和value。返回的是Entry接口
 * 最后发现keySet()的速度比entrySet()慢了很多。 
 */ 
public class HashMapTest     
{ 
    public static void main(String[] args)  
    { 
        HashMap<String,String> kmap = new HashMap<String,String>(); 
        HashMap<String, String> emap = new HashMap<String, String>();  
          
        for (int i = 0; i < 1000; i++)  
        { 
            kmap.put(""+i, "KEYSET"); 
        } 
        for (int i = 0; i < 1000; i++)  
        { 
            emap.put(""+i, "ENTRYSET"); 
        } 
         
        long stimes = System.currentTimeMillis(); 
        long ctimes = Calendar.getInstance().getTimeInMillis(); 
        long dtimes = new Date().getTime(); 
         
        //初始时间 这里用了三种取值方式 最后发现System.currentTimeMillis();是最直接的取值方法 
        System.out.println(stimes+" "+ctimes+"  "+dtimes); 
         
        Iterator<String> ktor = kmap.keySet().iterator(); 
        while(ktor.hasNext()) 
        { 
            System.out.println(kmap.get(ktor.next())); 
        } 
         
        long stimes1 = System.currentTimeMillis(); 
        long ctimes1 = Calendar.getInstance().getTimeInMillis(); 
        long dtimes1 = new Date().getTime(); 
         
        //结束时间并且也是entrySet的开始时间 
        System.out.println(stimes1+"    "+ctimes1+" "+dtimes1);
        System.out.println((stimes1-stimes)+"   "+(ctimes1-ctimes)+"    "+(dtimes1-dtimes)); 
         
         
        Iterator<Entry<String, String>> itor = emap.entrySet().iterator(); 
        while(itor.hasNext()) 
        { 
            Entry<String, String> e = itor.next(); 
            //System.out.println(e.getKey()); 
            System.out.println(e.getValue()); 
        } 
         
        long stimes2 = System.currentTimeMillis(); 
        long ctimes2 = Calendar.getInstance().getTimeInMillis(); 
        long dtimes2 = new Date().getTime(); 
        System.out.println(stimes2+"    "+ctimes2+" "+dtimes2); 
        System.out.println((stimes2-stimes1)+"  "+(ctimes2-ctimes1)+"   "+(dtimes2-dtimes1)); 
    } 
}