Java Collection-Collection-list-set-map-iterator learning Notes

1. Collection Interface

A collection can be understood as a dynamic array of objects, two meanings:

1), Dynamic: Objects in the set can be arbitrarily expanded and truncated;

2), the collection can hold arbitrary objects.

the collection has a higher performance than an array, and it is easier to extend and modify the data.

Common Subinterfaces for collection: List, Set, Queue.

2. List interface

The list collection can hold arbitrary objects, and objects in the collection can be duplicated.

List of common implementation classes: ArrayList, Vector.

Comparison of ArrayList with vectors:

Performance: ArrayList adopts asynchronous processing mode, high performance, vector synchronous processing, low performance;

Linear security aspect: ArrayList is non-thread safe, vector is thread safe.

"ArrayList instance"

<span style= "FONT-SIZE:14PX;" >import Java.util.arraylist;import Java.util.list;public class ListDemo1 {public static void main (string[] args) { list<string> lists = Null;lists = new arraylist<string> (); Lists.add ("Hello"); Lists.add ("World"); Lists.add ("Hello"); Allow objects in list to repeat for (int i=0; i< lists.size (); i++) {System.out.println (Lists.get (i));} System.out.println ("delete operation ...."); Lists.remove (2); for (int i = 0; I < lists.size (); i++) {System.out.println (Lists.get (i));} if (Lists.isempty ()) {System.out.println ("collection is empty ..."); else {System.out.println ("the collection is not empty ..."); if (Lists.contains ("World")) {System.out.println ("contains world" in the collection); System.out.println ("World where" is: "+ Lists.indexof (" World "));} else {System.out.println ("the collection does not contain world");} list<string> lists2 = new arraylist<string> () Lists2.add ("World"); Lists2.add ("Hello"); if (Lists.equals ( LISTS2) {//list is compared with the order in which elements are deposited System.out.println ("lists equals Lists2");} else {System.out.println ("lists and lists2 not Equal");} }}</span>

"Vector instance"

<span style= "FONT-SIZE:14PX;" >import Java.util.list;import Java.util.vector;public class VectorDemo1 {public static void main (string[] args) {List <String> lists = Null;lists = new Vector<string> (), Lists.add ("Hello"), Lists.add ("World"), for (int i = 0; I < ; Lists.size (); i++) {System.out.println (Lists.get (i))}}} </span>

3. Set interface

A repeating element cannot be placed in the set collection.

set sets are automatically sorted;

Set common implementation class: Hashset,treeset.

"HashSet instance"

Import Java.util.hashset;import Java.util.iterator;import Java.util.set;public class SetDemo1 {public static void main ( String[] args) {set<string> sets = Null;sets = new hashset<string> (); Sets.add ("D"); Sets.add ("A"); Sets.add ( "C"); Sets.add ("B"); Sets.add ("E");iterator<string> its = Sets.iterator (), while (Its.hasnext ()) {/* Iteration output */ System.out.println (Its.next ());} set<string> sets2 = null;sets2 = new hashset<string> (); Sets2.add ("E"); Sets2.add ("D"); Sets2.add ("A"); Sets2.add ("C"); Sets2.add ("B"); the If (Sets.equals (sets2)) {//Set comparison is independent of the order in which the elements are deposited System.out.println ("sets equals sets2!");} else {System.out.println ("Sets is not equal to sets2!");}}}

4. Iterator Interfaceiterator is the standard operation of the collection output.

Iterator is a collection of specialized iterative output interfaces that iterate over the elements to determine whether they have content or, if anything, take the content out.

For a concrete example, see the example above.

5. Map Interface

Map is saved in key/value form.

The common implementation class for map: Hashmap,hashtable.

Key duplication is not allowed.

"HashMap instance"

Import Java.util.collection;import java.util.hashmap;import Java.util.iterator;import Java.util.Map;import Java.util.set;public class MapDemo1 {public static void main (string[] args) {map<string, string> Map = new HASHMAP&L T String,string> (); Map.put ("Key1", "Hello"), Map.put ("Key2", "World"), Map.put ("Key3", "HI"); String s = map.get ("Key2"); Through key, get value; System.out.println (s); set<string> sets = Map.keyset (); Get all key;iterator<string> Iteskey = Sets.iterator (), while (Iteskey.hasnext ()) {System.out.println ( Iteskey.next ());} collection<string> cols = Map.values (); Get all the value; iterator<string> itesval = Cols.iterator (); while (Itesval.hasnext ()) {System.out.println (Itesval.next ());} if (Map.containskey ("Key1")) {System.out.println ("key exists");} if (Map.containsvalue ("World")) {System.out.println ("value exists");} Map.Remove ("Key1"); Remove the specified key}}

Java Collection-Collection-list-set-map-iterator learning Notes