Java Basic Syntax--arraylist collection

1.1 creation of collections

To create a common format for a collection:

Guide Package:import java.util.ArrayList;

To create an object: is identical to other common reference data types, but specifies the type of data stored in the container: arraylist< The data type of the element to be stored > variable name = new arraylist< The data type of the element to store > ();

the elements stored in the collection can only be The data type element specified in the <> brackets; the data type in the "< data type to store element >" must be a reference data type, not a basic data type;

The following is a representation of the reference data type for the 8 basic data Types :

Basic data types	The corresponding reference data type representation
Byte	Byte
Short	Short
I NT	Integer
Long	Long
Float	Float
Double	Double
Char	Character
Boolean	Boolean

1.2 common methods in collections

the ArrayList collection provides some common methods:

function Description

method declaration
Boo Lean Add ( object obj "	will specify the element obj Append to the end of the collection
Object get ( int index )	Returns the element at the specified position in the collection
int size ()	Returns the number of elements in the collection

Importjava.util.ArrayList; Public classArrayListDemo01 { Public Static voidMain (string[] args) {//Create ArrayList Collectionarraylist<string> list =NewArraylist<string>(); //adding elements to the collectionList.add ("STU1"); List.add ("STU2"); List.add ("Stu3"); List.add ("Stu4"); //gets the number of elements in the collectionSystem.out.println ("Length of the collection:" +list.size ()); //Remove and print the element at the specified positionSystem.out.println ("The 1th element is:" + list.get (0)); System.out.println ("The 2nd element is:" + list.get (1)); System.out.println ("The 3rd element is:" + list.get (2)); System.out.println ("The 4th element is:" + list.get (3)); }}

emphasize one point, The ArrayList collection is equivalent to a variable-length array, so access to the elements in the collection is indexed, the first element is stored at index 0 , and the second element is stored in index 1 position, and so on.

ArrayList Collection provides some common methods to complement;

Method declaration	Function description
Boolean add(int index, Object obj)	Inserts the specified element, obj , into the specified position in the collection
Object remve(int index)	Removes the element at the specified index from the collection , returning the element
void Clear()	Empties all elements in the collection
Object Set(int index, object obj)	replaces the element at the specified position in the collection with the specified element, obj

Boolean Add (int index, Object obj)

function: Specify the index position in the collection, add a new element, obj

function Description: Assume that the collection list has elements ["Java", "ee"], when using Add (1, "Javaweb"), the elements in the collection list are ["Java", "Javaweb", "Java ee"].

Object Set (int index, object obj)

function: replaces the element at the specified index position in the collection with the specified element, obj

function Description: Assume that the collection list has elements ["Java", "ee"], when using Set (0, "Javaweb"), the elements in the collection list are ["Javaweb", "Java ee"].

Object remve (int index)

function: Removes the element at the specified index from the collection, returning the element

function Description: Assume that the collection list has elements ["Java", "ee"], when you use Remove (0), the elements in the collection list are ["Java ee"], and the return value is "JavaScript".

void Clear ()

Function: Empties all elements in the collection

function Description: Assume that the collection list has elements ["Java", "EE"], and when clear () is used, the elements in the collection list are empty [].

1.3 traversal of a collection

The traversal of a collection is much like the traversal of an array, and is indexed by the way the collection is traversed as follows :

 Packagecn.itcastdemo02;Importjava.util.ArrayList;//traversal of a collection Public classArraylist { Public Static voidMain (string[] args) {ArrayList<Integer> list =NewArraylist<integer>(); List.add (23); List.add (1); List.add (43); List.add (25); List.add (55); List.add (28);  for(inti = 0;i<list.size (); i++) {System.out.println (List.get (i)); }}}

Java Basic Syntax--arraylist collection