Java Basics--about the traversal keyset and entryset__ traversal of the map

The first is a small example of traversal:

public static void Main (string[] args) {
        //TODO auto-generated method Stub
        map<string, string> maps = new H Ashmap<string, string> ();
        Maps.put ("A", "111a");
        Maps.put ("222", "222b");
        Maps.put ("333", "333c");
        Maps.put ("444", "444d");
        Maps.put ("555", "555e");
        Maps.put ("666", "666f");
        
        For (String Str:maps.keySet ()) {
            System.out.println (str + ":" + maps.get (str));
        }
        
        System.out.println ("--------------");
        
        For (entry<string, string> str:maps.entrySet ()) {
            System.out.println (str + "   " + str.getkey () + ":" + str.) GetValue ());
        }

    

As for the performance of the two:

The test found that the performance of the second approach is usually one-fold higher than the first method.

Examples are as follows:

Import Java.util.Calendar;
Import Java.util.Date;
Import Java.util.HashMap;
Import Java.util.Iterator;

Import Java.util.Map.Entry; /** * Test keyset () and EntrySet () Iteration time * Keyset (): After iteration, the key * EntrySet () can only be taken via get (): After iteration, E.getkey (), E.getvalue () take key and value. Returns the entry interface * The final description of the keyset () is slower than the EntrySet () a lot faster. It seems to be considered later with EntrySet () * @author YL * @date 2009.6.10/public class Hashmaptest {public static void main (string[] Ar
		GS) {hashmap<string,string> kmap = new hashmap<string,string> ();
		
		hashmap<string, string> emap = new hashmap<string, string> ();
		Load data for (int i = 0; i < 1000 i++) {kmap.put ("" +i, "YL");
		for (int i = 0; i < 1000 i++) {emap.put ("" +i, "ZT");
		Long stimes = System.currenttimemillis ();
		Long ctimes = Calendar.getinstance (). Gettimeinmillis ();
		
		Long dtimes = new Date (). GetTime ();
		
		Initial time here I used three kinds of value methods to find System.currenttimemillis (), the most direct method of System.out.println (stimes+ "" +ctimes+ "" +dtimes); iterator&Lt
		string> ktor = Kmap.keyset (). iterator ();
		while (Ktor.hasnext ()) {System.out.println (Ktor.next ());
		Long stimes1 = System.currenttimemillis ();
		Long ctimes1 = Calendar.getinstance (). Gettimeinmillis ();
		
		Long dtimes1 = new Date (). GetTime ();
		End world and also entryset start Time System.out.println ((stimes1-stimes) + "" + (Ctimes1-ctimes) + "" + (Dtimes1-dtimes));
		
		System.out.println (stimes1+ "" +ctimes1+ "" +dtimes1);
		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));
 }
}