Java Collection Knowledge Collation

1. Java Collection Class diagram

1. The difference between HashMap and Hashtable

	HashMap	HashTable
How to Inherit	Extends Abstractmap implements Map	Extends Dictionary implements Map
Thread Safety	Is	Whether
Efficiency relative ratio	High	Low
Allow null keys and values	Is	Whether
Determine which methods are included	Containsvalue and ContainsKey	Contains
Hash array Default Size	11,	16,
Hash array Increment mode	Old*2+1	2 Increase in Index

1. The traversal of the list

1list<string> list =NewArraylist<string>();2 3String prestring = "AA";4          for(intj = 0; J < 100000000; J + +) {5 List.add (prestring);6         }7 8         //Method 1 (fastest, list specific)9          for(inti = 0, Len = list.size (); i < Len; i++) {Ten List.get (i); One         } A  -         //Method 2 (for each-is the most time consuming) -          for(String tmp:list) { the         } -  -         //Method 3 (as with method 2,4, applies to all classes that implement the Iterable interface, which are common: queue,set,collection,list) -Iterator<string> iter =list.iterator (); +          while(Iter.hasnext ()) { -String str =Iter.next (); +         } A      at         //Method 4 -          for(Iterator<string> it2 =list.iterator (); It2.hasnext ();) { -String str =It2.next (); -}

Traversal of 2.map

1Hashmap<integer, string> map =NewHashmap<>();2String v = "value";3          for(inti=0;i<10000000;i++){4 Map.put (i, v);5         }6         7         //Method 1,8Iterator<map.entry<integer, string>> it1=Map.entryset (). iterator ();9          while(It1.hasnext ()) {TenMap.entry<integer, string> Entry =It1.next (); One             intKey =Entry.getkey (); AString value =Entry.getvalue (); -         } -      the         //Method 2 Gets the iterator for the key collection of map, which is 7 times times the time of Method 1.  -Iterator<integer> it2 =Map.keyset (). iterator (); -          while(It2.hasnext ()) { -             intKey =It2.next (); +String value =Map.get (key); -         } +     

Set and map traverse in a similar way, it is not here to wordy.

Java Collection Knowledge Collation