[Java] source code details: Three map traversal methods

Java programmers often come into contact with collection containers. Today, let's summarize the map Traversal method. The purpose is very simple. You can operate map freely. See the source code: [java] package dec; import java. util. collection; import java. util. hashMap; import java. util. iterator; import java. util. map; import java. util. map. entry; import java. util. set;/***** <p> * Title: map traversal test class/p> ** <p> * Description: example business class * </p> ** <p> * Copyright: Copyright (c) 2012 * </p> ** @ author dml @ 2012-12-25 * @ version 1.0 */public class MapIterator {public static void main (String [] args) {String [] str = {"I love you", "You love him", "He loves her", "She loves me"}; Map <Integer, string> m = new HashMap (); for (int I = 0; I <str. length; I ++) {m. put (I, str [I]);} System. out. println ("The following is the result output using useKeySet ():"); useKeySet (m); System. out. println ("The following is the result output using the useEntrySet () method:"); useEntrySet (m); System. out. println ("The following is the result output using useValues ():"); useValues (m);}/*** 1. use keySet to traverse ** Set java. util. map. keySet () ** Returns a Set view of the keys contained in this map. the set is backed * by the map, so changes to the map are reflected in the set, and * vice-versa. if the map is modified while an iteration over the set is in * progress (progress T through the iterator's own remove operation), the * results of the iteration are undefined. the set supports element removal, * which removes the corresponding mapping from the map, via the * Iterator. remove, Set. remove, removeAll, retainAll, and clear operations. * It does not support the add or addAll operations. ** Returns: a set view of the keys contained in this map ** @ param m */public static void useKeySet (Map m) {Set s = m. keySet (); Iterator it = s. iterator (); int Key; String value; while (it. hasNext () {Key = (Integer) it. next (); value = (String) m. get (Key); System. out. println (Key + ": \ t" + value) ;}}/*** 2. use entrySet to traverse ** Set java. util. map. entrySet () ** Returns a Set view of the mappings contained in this map. the set is * backed by the map, so changes to the map are reflected in the set, and * vice-versa. if the map is modified while an iteration over the set is in * progress (progress T through the iterator's own remove operation, or through * the setValue operation on a map entry returned by the iterator) the * results of the iteration are undefined. the set supports element removal, * which removes the corresponding mapping from the map, via the * Iterator. remove, Set. remove, removeAll, retainAll and clear operations. * It does not support the add or addAll operations. ** Returns: a set view of the mappings contained in this map ** @ param m */public static void useEntrySet (Map m) {Set s = m. entrySet (); Iterator it = s. iterator (); Map. entry entry; int Key; String value; while (it. hasNext () {entry = (Entry) it. next (); System. out. println (entry. getKey () + ": \ t" + entry. getValue () ;}}/*** 3. use values to traverse ** Collection <String> java. util. map. values () *** Returns a Collection view of the values contained in this map. the * collection is backed by the map, so changes to the map are reflected in * the collection, and vice-versa. if the map is modified while an iteration * over the collection is in progress (progress T through the iterator's own * remove operation), the results of the iteration are undefined. the * collection supports element removal, which removes the corresponding * mapping from the map, via the Iterator. remove, Collection. remove, * removeAll, retainAll and clear operations. it does not support the add or * addAll operations. ** Returns: a collection view of the values contained in this map ** @ param m */public static void useValues (Map <Integer, String> m) {Collection c = m. values (); Iterator it = c. iterator (); while (it. hasNext () {System. out. println (it. next () ;}} execution result: [plain] The following is the result output using the useKeySet () method: 0: I love you 1: You love him 2: he loves her 3: She loves me the following is the result output using the useEntrySet () method: 0: I love you 1: You love him 2: He loves her 3: the following figure shows the output result using useValues (): I love you love him He loves her She loves me