三种遍历map方式的时间比较

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            HashMap<String, String> kmap = new HashMap<String, String>();  

            HashMap<String, String> emap = new HashMap<String, String>();  

            HashMap<String, String> fmap = new HashMap<String, String>(); 

            //装数据  

            for (int i = 0; i < 1000; i++)   

            {  

                kmap.put(""+i, "YL");  

            }  

            for (int i = 0; i < 1000; i++)   

            {  

                emap.put(""+i, "ZT");  

            }  

            for (int i = 0; i < 1000; i++)   

            {  

                fmap.put(""+i, "FK");  

            }  

            long stimes = System.currentTimeMillis();  

            long ctimes = Calendar.getInstance().getTimeInMillis();  

            long dtimes = new Date().getTime();  

               

            //初始时间 这里我用了三种取值方式

            System.out.println(stimes+" "+ctimes+"  "+dtimes); 

  

            //keySet遍历map      

            Iterator<String> ktor = kmap.keySet().iterator();  

            while(ktor.hasNext())  

            {  

                System.out.print(ktor.next() + "=" + kmap.get(ktor.next()) + " ");  

            }  

               

            long stimes1 = System.currentTimeMillis();  

            long ctimes1 = Calendar.getInstance().getTimeInMillis();  

            long dtimes1 = new Date().getTime();     

            System.out.println(stimes1+"    "+ctimes1+" "+dtimes1); 

            System.out.println((stimes1-stimes)+"   "+(ctimes1-ctimes)+"    "+(dtimes1-dtimes));  

             

            //entrySet遍历map 

            Iterator<Entry<String, String>> itor = emap.entrySet().iterator();  

            while(itor.hasNext())  

            {  

                Entry<String, String> e = itor.next();   

                System.out.print(e.getKey() + "=" + 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));  

 

            //for循环遍历 

            for (Map.Entry entry : fmap.entrySet()) 

            { 

                System.out.print(entry.getKey() + "=" + entry.getValue() + " ");

            }

 

            long stimes3 = System.currentTimeMillis();  

            long ctimes3 = Calendar.getInstance().getTimeInMillis();  

            long dtimes3 = new Date().getTime();  

            System.out.println(stimes3+"    "+ctimes3+" "+dtimes3);  

            System.out.println((stimes3-stimes2)+"  "+(ctimes3-ctimes2)+"   "+(dtimes3-dtimes2));  




输出结果: