Java Basics 5--Collection Class (Set,list,map) and iterator iterator use

Write a very good summary: http://blog.csdn.net/speedme/article/details/22398395#t1

Here's a look at how each collection uses an iterator iterator to get an element:

1.list using iterators iterator

 Public classTestarraylist { Public Static voidMain (String args[]) {F1 ();    F2 (); }     Public Static voidF1 () {List<String> strlist =NewArraylist<string>();  for(inti = 0; I < 10; i++) {Strlist.add ("String" +i); } Iterator<String> iterator = Strlist.iterator ();//List.iterator ()         while(Iterator.hasnext ())//determines whether the elements in the collection are traversed, and if not, returns True        {            if(Iterator.next (). Equals ("String3") ) {iterator.remove (); //iterator.remove () removes the object obtained from the most recent iterator.next ()}} iterator= Strlist.iterator ();//This step is important to redefine the iterator after deletion         while(Iterator.hasnext ()) {System.out.println (Iterator.next ());//Iterator.next () returns the next element        }    }         Public Static voidF2 () {//1. Adding elements to the ArrayListArrayList ArrayList=NewArrayList (); Arraylist.add ("Wyy");//Arraylist.addArraylist.add ("12"); Arraylist.add ("Huhu"); Arraylist.add ("897"); System.out.println ("Output entire arrayList" + arrayList);//[Wyy, Huhu, 897]             for(inti = 0; I < arraylist.size (); i++) {System.out.println (Arraylist.get (i)); } Iterator<String> A =Arraylist.iterator (); System.out.println ("The rest of the elements are:");  while(A.hasnext ()) {if(A.next (). Equals ("12") ) {a.remove (); }            }//Use for Loop, can save memory, general use when developing             for(A = Arraylist.iterator (); A.hasnext ();)//Note that if you delete the result after the decision, you must re-define the iterator to remove the remaining data{System.out.println (A.next ()); }        }}

2.set using iterators iterator

 Packagecollection;ImportJava.util.HashSet;ImportJava.util.Iterator;ImportJava.util.Set;ImportJava.util.TreeSet;/*** Created by Wyy on 2017/2/20.*/ Public classSettest { Public Static voidMain (string[] args) {//common methods of set:Set set =NewHashSet (); Set.add ("Wq"); Set.add ("ER"); Set.add ("ER"); Set.add ("Gee"); Set.add ("Wdd"); Set.add ("3242");        SYSTEM.OUT.PRINTLN (set); Set SortedSet=NewTreeSet (set);//the added elements must be valid to compare the sort, with CompareTo     /*Sortedset.add (New Settest ()); Error: Collection. Settest cannot is cast to java.lang.Comparable add element must be comparable*/System.out.println (sortedSet);//[3242, er, gee, WDD, Wq], the second output of the list is sorted alphabetically. String a= "a"; String b= "a"; System.out.println (A.hashcode ());// $System.out.println (B.hashcode ());// theIterator Iterator=set.iterator ();//creates an iterator to the collection that takes the element         while(Iterator.hasnext ()) {Object obj=Iterator.next ();        System.out.println (obj); }    }}

3.map using iterators, there are 4 ways

 Packagecollection;ImportJava.util.*;/*** Created by Wyy on 2017/2/21.*/ Public classMaptest { Public Static voidMain (string[] args) {Map<Integer,String> map=NewHashmap<>(); Map.put (1, "Wo"); Map.put (2, "Chi"); Map.put (3, "XI"); Map.put (4, "Gua"); System.out.println (Map.size ());/*Method 1: Use set to store the value of key, and then use the For loop to get the value*/Set<Integer> Set=map.keyset ();//get the value of all keys         for(intI:set) {String value=map.get (i);//Gets the valueSystem.out.println (value); }/*Method 2: Use map.entryset<> construct iterator to traverse key and value*/Iterator<Map.Entry<Integer,String>> it=Map.entryset (). iterator ();  while(It.hasnext ()) {Map.entry<Integer,String> entry=It.next (); System.out.println ("The key is:" +entry.getkey () + ", and the value is:" +Entry.getvalue ()); }/*Method 3: Recommended to traverse key and value through Map.entryset, especially when large capacity*/         for(map.entry<integer,string>En:map.entrySet ()) {System.out.println ("The key is:" +en.getkey () + ", and the value is:" +En.getvalue ()); }        /*Method 4: You can only get values of value*/         for(String v1:map.values ()) {System.out.println ("The value is:" +v1); }    }}

Java Basics 5--Collection Class (Set,list,map) and iterator iterator use