Two programs about containers

When two learning containers are attachedProgram, Easy to review.

1. Test the traversal of list, set, and map sets.

/*** Test the traversal operation of list, set, and map sets * when traversing containers in the future, the List should adopt index traversal as much as possible, and the set should adopt the iterator as much as possible **/package COM. bjsxt. test. collection; import Java. util. arraylist; import Java. util. collection; import Java. util. hashmap; import Java. util. hashset; import Java. util. iterator; import Java. util. list; import Java. util. map; import Java. util. map. entry; import Java. util. set; public class testiterate {public static void testlist () {list <student> List = new arraylist <student> (); list. add (new student ("James"); list. add (new student ("Li Si"); list. add (new student ("Wang Wu"); list. add (new student ("Zhao "); // use the index to traverse for (INT I = 0; I <list. size (); I ++) {student stu1 = List. get (I); system. out. println (stu1.getname ();} // use the enhanced for loop for (student STU: List) {system. out. println (Stu. getname ();} // use iterator. This method can iterate both list and setiterator <student> iter = List. iterator (); While (ITER. hasnext () {student stu2 = ITER. next (); // returns the current element and points the cursor to the next system. out. println (stu2.getname ();} // or use the following method for (iterator <student> iter2 = List. iterator (); iter2.hasnext ();) {student Stu = iter2.next (); system. out. println (Stu. getname () ;}} public static void testset () {set <student> set = new hashset <student> (); set. add (new student ("James"); set. add (new student ("Li Si"); set. add (new student ("Wang Wu"); set. add (new student ("Zhao "); // use the enhanced for loop for (student STU: Set) {system. out. println (Stu. getname ();} // use iterator (list or set can be iterated) iterator <student> iter = set. iterator (); While (ITER. hasnext () {student Stu = ITER. next (); system. out. println (Stu. getname () ;}for (iterator <student> iter2 = set. iterator (); iter2.hasnext ();) {student Stu = iter2.next (); system. out. println (Stu. getname () ;}} public static void testmap () {Map <string, student> map = new hashmap <string, student> (); map. put ("A", new student ("Zhang San"); map. put ("B", new student ("Li Si"); map. put ("C", new student (""); // traverses keyset <string> set1 = map. keyset (); // Why does iterator <string> iter1 = set1.iterator (); While (iter1.hasnext () {string key = iter1.next (); system. out. println (Key + "-----" + map. get (key ). getname ();} // traverse valuecollection <student> set2 = map. values (); iterator <student> iter2 = set2.iterator (); While (iter2.hasnext () {student v = iter2.next (); system. out. println (v. getname ();} // traverses the entry (key-Value Pair) set <entry <string, student> set3 = map. entryset (); iterator <entry <string, student> iter3 = set3.iterator (); While (iter3.hasnext () {entry <string, student> E = iter3.next (); system. out. println (E. getkey () + "-----" + E. getvalue () ;}} public static void main (string [] ARGs) {testlist (); testset (); testmap ();}}

2. Use Map to classify and count elements in a string

Import Java. util. hashmap; import Java. util. iterator; import Java. util. map; import Java. util. map. entry; import Java. util. set; import Java. util. stringtokenizer; public class testhashmap {public static void main (string [] ARGs) {string STR = "what a Woderful day A what"; Map <string, integer> map = new hashmap <string, integer> (); // construct the container stringtokenizer S = new stringtokenizer (STR); While (S. hasmoreelements () {s Tring strtemp = (string) S. nextelement (); // forcibly convert the object type to string type // store if (! Map. containskey (strtemp) {// empty bag map. put (strtemp, 1); // create a container and put it into the value} else {map. put (strtemp, map. get (strtemp) + 1) ;}/// method 1 // traverse the key in the map, iterator + keyset/get <recommended> set <string> key = map. keyset (); iterator <string> iter1 = key. iterator (); While (iter1.hasnext () {string str1 = iter1.next (); system. out. println (str1 + "--->" + map. get (str1);} // use enhanced for + keyset/get for (string keys: Key) {system. out. println (Key + "--->" + map. get (KEYS);} // method 2 // use entryset + foreach + iterator set <map. entry <string, integer> entry = map. entryset (); iterator <map. entry <string, integer> iter2 = entry. iterator (); While (iter2.hasnext () {map. entry <string, integer> en = iter2.next (); string key2 = en. getkey (); integer it1 = en. getvalue (); system. out. println (key2 + "--->" + map. get (key2);} // foreachfor (Entry <string, integer> entry2: entry) {string key3 = entry2.getkey (); integer it2 = entry2.getvalue (); system. out. println (key3 + "--->" + map. get (key3);}/* This is the element in the print string ** while (S. hasmoretokens () {system. out. println (S. nexttoken ());}*/}}