[Java learning notes] examples of keySet, entrySet, and values in Map sets, keysetentryset

[Java learning notes] examples of keySet, entrySet, and values in Map sets, keysetentryset

1 import java. util. collection; 2 import java. util. hashMap; 3 import java. util. iterator; 4 import java. util. map; 5 import java. util. set; 6 7 public class MapDemo {8 9 public static void main (String [] args) {10 Map <Integer, String> map = new HashMap <Integer, String> (); 11 12 13 map. put (8, "zhaoliu"); 14 map. put (9, "zhaoliu"); 15 map. put (1, "xiaoqiang"); 16 map. put (6, "wangcai"); 17 map. put (7, "zhaoliu"); 18 Map. put (99, "zhaoliu"); 19 map. put (87, "xiaoqiang"); 20 map. put (42, "wangcai"); 21 22 show1 (map); 23 24 show2 (map); 25 26 showValue (map ); 27 28} 29 30 public static void showValue (Map <Integer, String> map) {31 Collection <String> values = map. values (); 32 Iterator <String> it = values. iterator (); 33 while (it. hasNext () 34 {35 System. out. println (it. next (); 36} 37} 38 39 public static void show2 (Map <Integer, String> map) {40 // You Can iterate 41 by converting Map to Set. // another method is found. EntrySet42 // This method stores the key-value ing relationship as an object in the Set, and the ing type is Map. entry type (Marriage Certificate) 43 44 Set <Map. entry <Integer, String> entrySet = map. entrySet (); 45 Iterator <Map. entry <Integer, String> it = entrySet. iterator (); 46/* 47 * can also be written as Iterator <Map. entry <Integer, String> it = map. entrySet (). iterator (); 48 */49 50 while (it. hasNext () 51 {52 Map. entry <Integer, String> me = it. next (); 53 Integer key = me. getKey (); 54 String va Lue = me. getValue (); 55 System. out. println (key + ":" + value); 56 57} 58} 59 60 public static void show1 (Map <Integer, String> map) {61 // retrieve all elements in the map. 62 // Principle: The keySet method is used to obtain the Set where all the keys in the map are located, and each key is obtained through the Set iterator, 63 // obtain the value of each key through the get method of the map set. 64 65 Iterator <Integer> it = map. keySet (). iterator (); 66/* 67 * is equivalent to Set <Integer> keySet = map. keySet (); 68 * Iterator <Integer> it = keySet. iterator (); 69*70 */71 72 while (it. hasNext () 73 {74 Integer key = it. next (); 75 String value = map. get (key); 76 System. out. println (key + "=" + value); 77} 78} 79 80}