A collection is a container. Collections and arrays are different: only for storing objects, the collection length is variable, the array can only exist the same type of object, the collection may save any object. Collection |--list: Elements are ordered, elements can be duplicated because the set reminds of an indexed |--arraylist: the underlying data structure uses an array, the query is fast, and the deletion is slightly slower. is not synchronized, easy to out of security risks. Single-threaded, high efficiency. |--linkedlist: The underlying data structure uses the linked list data structure, the query speed is slow, adding and deleting fast |--vetor: The bottom is the array data structure. Victor is synchronous, progress is not |--set: element No, non-repeatable, no index |--hashset: the underlying data structure is a hash table. |--treeset
Collection collection is an interface that contains references to objects that are stored in a collection of ArrayList and LinkedList and vectors three main classes. The main methods are introduced: Take ArrayList as an example import java.util.*;p ublic class Test { public static void Main (String adgs[]) { ArrayList al = new ArrayList (); ArrayList al2 = new ArrayList (); al2.add ("PPP"); Al2.add ("KKK"); nbsp; //1, add element Al.add ("JAVA1"); al.add ("Java2"); al.add ("Java3"); Al.add (" Java4 "); //2, get length SOP (" Size: "+al.size ()); //3, print set SOP (AL); //4, Delete elements Al.remove ("java2"); Use the object's equals to determine if the same SOP (AL); //5, empty collection al.clear (); SOP (AL); Al.add (" JAVA1 "); al.add (" Java2 "); al.add (" Java3 "); al.add (" java4 "); //6, judging elements SOP (" Whether the JAVA1 exists "+al.contains (" JAVA1 ")); //equals //7, add collection addall al.addall (AL2); sop (AL); //8, intersect, store in Al Al.clear (); al2.clear (); al.add ("JAVA1"); Al.add ("Java2"); al.add ("Java3"); al.add ("java4"); Al2.add ("PPP"); Al2.add ("KKK"); Al2.add ("Java3"); al2.add ("java4"); Al.retainall (AL2); sop (AL); //9, differential set al/al2 Al.removeall (Al2); //10,containsall () returns TRUE or false } public static void SOP (Object O) { System.out.println (o); }}
iterator class: InteratorRemove and manipulate elements: unifies the way the collection elements are taken out. Use procedure: Get object Interator it = Collection.iterator (); Method Object It.next ()//Remove Element Boolean it.hasnext ()//Determine if there are elements to remove import ja va.util.*;p Ublic class Test {public static void main (String adgs[]) {ArrayList Al = new ArrayList (); 1, add Element Al.add ("JAVA1"); Al.add ("Java2"); Al.add ("Java3"); Al.add ("Java4"); /* Iterator it = al.iterator ();//Gets the iterator that is used to remove the element in the collection while (It.hasnext ()) SOP (It.next ()); */for (Iterator it = Al.iterator (); It.hasnext ();)//This notation saves memory sop (It.next ());} public static void sop (Object o) {Sys Tem.out.println (o); }}
List
List-specific common methods: The method that can operate the angle is added add (index,element) addall (index,collection) Delete (index) change set (Index,element)//el E: element Check get (index) sublist (from,to) Listiterator ()
ArrayListImport java.util.*;p Ublic class Test {public static void main (String adgs[]) {ArrayList Al = new ArrayList (); add Element Al.add ("Java01"); Al.add ("Java02"); Al.add ("java03"); SOP ("meta-set" +al); Al.add (1, "java09"); SOP (AL); Deletes the specified position element Al.remove (2); SOP (AL); Modify the element Al.set (1, "JJJ"); SOP (AL); Check SOP ("1:" +al.get (1)); Gets all the elements. for (int x=0;x<al.size (); x + +) SOP ("Al ()" +al.get (x)); Get the position of the object via IndexOf SOP (Al.indexof ("java03")); List sub = al.sublist (1, 3); SOP (sub); } public static void sop (Object o) {System.out.println (o);}}
List iteratorsImport java.util.*;p Ublic class Test {public static void main (String adgs[]) {ArrayList Al = new ArrayList (); Al.add ("Java01"); Al.add ("Java02"); Al.add ("java03"); Iterator it = Al.iterator (); while (It.hasnext ()) {Object obj = It.next (); if (Obj.equals ("JAVA02")) It.remove (); The JAVA02 is removed from the collection. However, the Al.add () operation is not supported//the exception SOP (obj) is thrown; } SOP (AL); } public static void sop (Object o) {System.out.println (o);}} So there's the list iterator:
LinkedList
Unique method: AddFirst (obj);//Add objaddlast (obj) at the very beginning of ll; GetFirst (); , tail getlast (); Removefirst ();//Gets the element, but the element is deleted. If there are no elements, an exception occurs. Removelast ();
ArrayList Practice
The core of removing duplicate objects is to override the Equals method of the object to note the application of type-conversion polymorphism.
Set
set Interface: The element is not required and cannot be duplicated. The function of set is to establish the object when the collection is consistent with the HashSet
JAVA 13 (Collection Framework)
