Java Collection knowledge sorting, java Collection knowledge

Java Collection knowledge sorting, java Collection knowledge

 

 

	HashMap	HashTable
Inheritance Method	extends AbstractMap implements Map	extends Dictionary implements Map
Thread Security	No	Yes (all methods are modified by synchronized)
Relative Efficiency	High	Low
Null keys and values are allowed.	Yes	No
Methods for determining inclusion	Containsvalue and containsKey	Contains
Default hash array size	11	16
Add hash Array	Old * 2 + 1	2 index increase

 

1 List <String> list = new ArrayList <String> (); 2 3 String preString = "aa"; 4 for (int j = 0; j <100000000; j ++) {5 list. add (preString); 6} 7 8 // method 1 (fastest, List exclusive) 9 for (int I = 0, len = list. size (); I <len; I ++) {10 list. get (I); 11} 12 13 // method 2 (for each-most time-consuming) 14 for (String tmp: list) {15} 16 17 // method 3 (same as method 2 and 4, applicable to all classes that implement the Iterable interface, common ones include Queue, Set, Collection, List) 18 Iterator <String> iter = list. iterator (); 19 while (iter. hasNext () {20 String str = iter. next (); 21} 22 23 // method 424 for (Iterator <String> it2 = list. iterator (); it2.hasNext ();) {25 String str = it2.next (); 26}

 

2. map Traversal

 

1 HashMap <Integer, String> map = new HashMap <> (); 2 String v = "value"; 3 for (int I = 0; I <10000000; I ++) {4 map. put (I, v); 5} 6 7 // method 1, 8 Iterator <Map. entry <Integer, String> it1 = map. entrySet (). iterator (); 9 while (it1.hasNext () {10 Map. entry <Integer, String> entry = it1.next (); 11 int key = entry. getKey (); 12 String value = entry. getValue (); 13} 14 15 // method 2 gets the iterator of the map key set, 7 times the time consumed by method 1. 16 Iterator <Integer> it2 = map. keySet (). iterator (); 17 while (it2.hasNext () {18 int key = it2.next (); 19 String value = map. get (key); 20} 21

 

The Traversal method of set and map is similar.