Common operations for list collections in Java

Directory:

1. List to add, get, delete elements;
2. Whether the list contains an element;
3. The value of the element is changed (replaced) by the index in the list;
4. The index of the view (judging) element in the list;
5. Judging by the index position of the element;
6. Regenerate a new list (intercept collection) using the index position in the list;
7. Compares all the elements in the two list;
8. Determines whether the list is empty;
9. Returns the Iterator collection object;
10. Converts a collection to a string;
11. Converts a collection into an array;
12. collection type conversion;
13. to repeat;

Note: The code in the content is associative.

1.list Add, get, delete element;

The Add method is:. Add (E); Get method is:. Get (index); Delete method:. Remove (index); Delete by index; remove (Object o); Delete by element content;

List<string> person=new arraylist<> ();p Erson.add ("Jackie");//index is 0//.add (e) person.add ("Peter");// Index is 1person.add ("Annie");//Index is 2person.add ("Martin");//Index is 3person.add ("marry");//Index is 4person.remove (3);//.remove ( Index) Person.remove ("Marry"),//.remove (Object o) String per= "";p er=person.get (1); System.out.println (per); . Get (index) for (int i = 0; i < person.size (); i++) {System.out.println (Person.get (i));//.get (Index)}

Whether an element is included in the 2.list;

Method:. Contains (Object o); returns True or False

List<string> fruits=new arraylist<> () fruits.add ("Apple"); Fruits.add ("banana"); Fruits.add ("peach");// For loop traversal listfor (int i = 0; i < fruits.size (); i++) {System.out.println (Fruits.get (i));} String applestring= "Apple",//true or FalseSystem.out.println ("Fruits contains apple:" +fruits.contains (applestring)); if ( Fruits.contains (applestring)) {System.out.println ("I like to eat apples");} else {System.out.println ("I'm not Happy");}

The value of the element is changed (replaced) in 3.list according to the index;

Note. Set (index, Element); and. Add (index, Element); the difference;

String a= "White Dragon Horse", b= "Sand Monk", c= "eight commandments", d= "Tang priest", e= "Wukong"; List<string> people=new arraylist<> ();p Eople.add (a);p Eople.add (b);p Eople.add (c);p eople.set (0, d);//. Set (index, Element),//to place D Tang to the list index 0, replace a white Dragon horse People.add (1, e),//.add (index, Element),//To place e Wukong in the list index 1 position, The original position of the B-sand monk moves back one//enhanced for Loop traversal listfor (String str:people) {System.out.println (str);}

The index of the viewing (judging) element in 4.list;　

Note: The difference between indexOf (); and lastIndexOf ();

List<string> names=new arraylist<> () names.add ("Liu Bei");//Index is 0names.add ("Guan Yu");//Index is 1names.add ("Zhang Fei");// The index is 2names.add ("Liu Bei");//Index is 3names.add ("Zhang Fei");//Index is 4SYSTEM.OUT.PRINTLN (Names.indexof ("Liu Bei")); System.out.println (Names.lastindexof ("Liu Bei")); System.out.println (Names.indexof ("Zhang Fei")); System.out.println (Names.lastindexof ("Zhang Fei"));

5. Judging by the index position of the element;

if (Names.indexof ("Liu Bei") ==0) {System.out.println ("Liu Bei Here");} else if (Names.lastindexof ("Liu Bei") ==3) {System.out.println ("Liu Bei Is There");} else {System.out.println ("Where is Liu Bei?") ");}

6. Regenerate a new list (intercept collection) using the index position in the list;

Methods:. Sublist (FromIndex, Toindex);. Size (); The method gets the number of elements in the list and

List<string> phone=new arraylist<> ();p hone.add ("Samsung");//Index for 0phone.add ("Apple");//Index for 1phone.add ("Hammer");// Index is 2phone.add ("Huawei");//Index is 3phone.add ("millet");//index is 4//the original list is traversed for (String Pho:phone) {System.out.println (pho);} Generate new Listphone=phone.sublist (1, 4);//.sublist (FromIndex, Toindex)//Use the object of index 1-4 to regenerate a list, but not the element with index 4, 4-1=3for ( int i = 0; I < phone.size (); i++) {//Phone.size () The method gets the number of elements in the list and the System.out.println ("The new list contains the element is" +phone.get (i));}

7. Compare all the elements in the two list;

The Equals method of two equal objects must be true, but two hashcode equal objects are not necessarily equal objects

1.
if (person.equals (fruits)) {System.out.println ("All elements in two list are the same");} else {System.out.println ("all elements in the two list are not the same");} 2.if (Person.hashcode () ==fruits.hashcode ()) {System.out.println ("We are the same");} else {System.out.println ("We are not the same");}

8. Determine if the list is empty;

NULL returns TRUE, non-null returns false

if (Person.isempty ()) {System.out.println ("Empty");} else {System.out.println ("not Empty");}

9. Returns the Iterator collection object;

System.out.println ("Return iterator Collection object:" +person.iterator ());

1+0. Converting a collection to a string;

String listring= ""; listring=person.tostring (); System.out.println ("Converts the collection to a string:" +listring);

11. Convert the set to an array;

System.out.println ("Convert collection to array:" +person.toarray ());

12. Set type conversion;

1. Default Type list<object> listsstrings=new arraylist<> (); for (int i = 0; i < person.size (); i++) {Listsstrings.add (Person.get (i));}　　2. Specified type list<stringbuffer> lst=new arraylist<> (); for (string String:person) {Lst.add (StringBuffer (String));}

13. To repeat;

List<string> lst1=new arraylist<> () lst1.add ("AA"); Lst1.add ("DD"); Lst1.add ("ss"); Lst1.add ("AA"); Lst1.add ("ss");                   Method 1.for (int i = 0; I <lst1.size ()-1; i++) {for (int j = lst1.size ()-1; J >i; j--) {if (Lst1.get (j). Equals (LST1.G ET (i))) {Lst1.remove (j);}}} System.out.println (lst1);                   Method 2.list<string> lst2=new arraylist<> (); for (String S:lst1) {if (Collections.frequency (Lst2, s) <1) { Lst2.add (s);}} System.out.println (LST2);

Complete code is included:

Package Mytest01;import Java.util.arraylist;import Java.util.list;public class ListTest01 {public static void main ( String[] args) {//list Add, get, delete element list<string> person=new arraylist<> ();p Erson.add ("Jackie");//index is 0//. Add (E) Person.add ("Peter");//Index is 1person.add ("Annie");//Index is 2person.add ("Martin");//Index is 3person.add ("marry");// The index is 4person.remove (3),//.remove (index) person.remove ("Marry"),//.remove (Object o) String per= "";p er=person.get (1); System.out.println (per); . Get (index) for (int i = 0; i < person.size (); i++) {System.out.println (Person.get (i));//.get (index)}// The list always contains an element list<string> fruits=new arraylist<> () fruits.add ("Apple"); Fruits.add ("banana"); Fruits.add ("Peach") );//for loop traversal listfor (int i = 0; i < fruits.size (); i++) {System.out.println (Fruits.get (i));} String applestring= "Apple",//true or FalseSystem.out.println ("Fruits contains apple:" +fruits.contains (applestring)); if ( Fruits.contains (applestring)) {System.out.println ("I like to eat apples");} else {System.out.println ("I'm not Happy");} The list is based on the cableChange the element value (replace) String a= "White Dragon Horse", b= "Sand Monk", c= "eight commandments", d= "Tang priest", e= "Wukong"; List<string> people=new arraylist<> ();p Eople.add (a);p Eople.add (b);p Eople.add (c);p eople.set (0, d);//. Set (index, Element)//position D Tang to list index 0, replace a white Dragon horse People.add (1, e),//.add (index, Element),//Put e Wukong into the list index 1 position, The original position of the B-sand monk moves back one//enhanced for Loop traversal listfor (String str:people) {System.out.println (str);} The index of the view (judging) element in list list<string> names=new arraylist<> (); Names.add ("Liu Bei");//Index is 0names.add ("Guan Yu");// The index is 1names.add ("Zhang Fei");//Index is 2names.add ("Liu Bei");//Index is 3names.add ("Zhang Fei");//Index is 4SYSTEM.OUT.PRINTLN (Names.indexof ("Liu Bei")); System.out.println (Names.lastindexof ("Liu Bei")); System.out.println (Names.indexof ("Zhang Fei")); System.out.println (Names.lastindexof ("Zhang Fei"));//Depending on the index position of the element if (Names.indexof ("Liu Bei") ==0) {System.out.println (" Liu Bei is Here ");} else if (Names.lastindexof ("Liu Bei") ==3) {System.out.println ("Liu Bei Is There");} else {System.out.println ("Where is Liu Bei?") ");} Regenerate a new list (intercept collection) using the index position in the list list<string> phone=new arraylist<> ();p hone.add ("Samsung");//index is 0phone.add ( "Apple");//IndexIs 1phone.add ("Hammer");//Index is 2phone.add ("Huawei"),//Index is 3phone.add ("millet"),//index is 4//the original list to traverse for (String Pho:phone) { System.out.println (pho);} Generate new Listphone=phone.sublist (1, 4);//.sublist (FromIndex, Toindex)//Use the object of index 1-4 to regenerate a list, but not the element with index 4, 4-1=3for ( int i = 0; I < phone.size (); i++) {//Phone.size () The method gets the number of elements in the list and the System.out.println ("The new list contains the element is" +phone.get (i));} Compare the Equals method of all elements in two list//two equal objects must be true, but two hashcode equal objects are not necessarily equal objects if (person.equals (fruits)) {System.out.println ("All elements in the two list are the same");} else {System.out.println ("all elements in the two list are not the same");} if (Person.hashcode () ==fruits.hashcode ()) {System.out.println ("We are the same");} else {System.out.println ("We are not the same");} Returns true if the list is empty//empty, and returns Falseif (Person.isempty ()) {System.out.println ("empty") if not null;} else {System.out.println ("not Empty");} Returns the Iterator collection object System.out.println ("Returns iterator Collection object:" +person.iterator ());//Converts the collection to string listring= ""; listring= Person.tostring (); System.out.println ("Convert collection to String:" +listring);//Convert collection to an array, default type System.out.println ("Convert collection to array:" +person.toarray ());//// Turn the collectionChange to the specified type (friendly handling)//1. Default Type list<object> listsstrings=new arraylist<> (); for (int i = 0; i < person.size (); i++) { Listsstrings.add (Person.get (i)); 2. Specify the type list<stringbuffer> lst=new arraylist<> (); for (String String:person) {Lst.add (StringBuffer ( string));}} private static StringBuffer StringBuffer (String string) {return null;}}

Common operations for list collections in Java