JDK5.0 new feature-Enhanced for loop

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Enhanced for Loop
Its underlying implementation is the use of iterator.
What containers can use enhanced for? -----------iterable

The disadvantage of enhanced for is that it can only be traversed and cannot be manipulated during traversal.

Enhanced for format
For (type reference: Container) {
}
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About iterating over a collection.
List
1.Iterator
2. Enhanced for
3. General for
4.ListIterator
Set
1. Enhanced for
2.Iterator
Map
1.keySet---Get a set view of all keys
2.entryset--get the set view of Key-value

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Iterating over a list

 PackageCn.itcast.fordemo;Importjava.util.ArrayList;ImportJava.util.Iterator;Importjava.util.List;ImportJava.util.ListIterator;ImportJava.util.Random;Importorg.junit.Test;//code is required//iterating over a list Public classDemo1 {//1. Using a traditional iterator@Test Public voiddemo1 () {List<Integer> list =NewArraylist<integer>();  for(inti = 0; I < 10; i++) {List.add (NewRandom (). Nextint (100)); }        //For (iterator<integer> it = List.iterator (); It.hasnext ();) {        //System.out.println (It.next ()); // }Iterator<Integer> it =List.iterator ();  while(It.hasnext ()) {System.out.println (It.next ()); }    }    //2.----Benefits of using Listiterator: 1. You can traverse 2 down or up. The add set operation can be performed during traversal .@Test Public voidDemo2 () {List<Integer> list =NewArraylist<integer>();  for(inti = 0; I < 10; i++) {List.add (NewRandom (). Nextint (100)); } listiterator<Integer> it =List.listiterator ();  while(It.hasnext ()) {System.out.println (It.next ()); }    }    //3. Use normal for size get@Test Public voidDemo3 () {List<Integer> list =NewArraylist<integer>();  for(inti = 0; I < 10; i++) {List.add (NewRandom (). Nextint (100)); }         for(inti = 0; I < list.size (); i++) {System.out.println (List.get (i)); }    }    //4. Enhanced for@Test Public voidDemo4 () {List<Integer> list =NewArraylist<integer>();  for(inti = 0; I < 10; i++) {List.add (NewRandom (). Nextint (100)); }         for(intn:list)        {System.out.println (n); }    }}

Iterating over a set set

 PackageCn.itcast.fordemo;ImportJava.util.HashSet;ImportJava.util.Iterator;ImportJava.util.Set;Importorg.junit.Test;//iterating over a set set Public classDemo2 {//iterators@Test Public voiddemo1 () {Set<String> set =NewHashset<string> ();//use hashcode with equals to maintain uniqueness.Set.add ("Def"); Set.add ("123"); Set.add ("ABC");  for(Iterator<string> it =set.iterator (); It.hasnext ();)        {System.out.println (It.next ()); }    }        //Enhanced for@Test Public voidDemo2 () {Set<String> set =NewHashset<string> ();//use hashcode with equals to maintain uniqueness.Set.add ("Def"); Set.add ("123"); Set.add ("ABC");  for(String s:set) {System.out.println (s); }    }}

Map traversal

 PackageCn.itcast.fordemo;ImportJava.util.HashMap;ImportJava.util.Map;ImportJava.util.Set;Importorg.junit.Test;//Map Traversal Public classDemo3 {//using keyset@Test Public voiddemo1 () {Map<string, string> map =NewHashmap<string, string>(); Map.put ("First", "AAAA"); Map.put ("Second", "BBBB"); Set<String> keys = Map.keyset ();//It's first,second in keys.         for(String key:keys) {System.out.println ("Key:" + key + "VALUE:" +Map.get (key)); }    }    //using EntrySet@Test Public voidDemo2 () {Map<string, string> map =NewHashmap<string, string>(); Map.put ("First", "AAAA"); Map.put ("Second", "BBBB"); Set<map.entry<string, string>> set =Map.entryset ();  for(Map.entry<string, string>Entry:set) {System.out.println (Entry.getkey ()+ "   " +Entry.getvalue ()); }    }}

Arrays can also be traversed using enhanced for

 Package Cn.itcast.fordemo; Import org.junit.Test;  Public class Demo4 {    @Test    //  arrays can also traverse public void using enhanced for     Demo () {        int[] arr={1,2,3,4,5};                  for (int  n:arr) {            System.out.println (n);     }}}

JDK5.0 new feature-Enhanced for loop