Java ArrayList Collection

The ArrayList collection is the most common collection in a program, which belongs to the reference data type (Class). A variable-length array is encapsulated inside the ArrayList, and when the deposited element exceeds the lengthof the array,ArrayList allocates a larger array in memory to store the elements. the ArrayList collection can therefore be thought of as a variable-length array.

The creation format of the collection

Guide Package:import java.util.ArrayList;

Create objects: Exactly the same way as other normal reference data types, but specify the data types 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 > ();

L The elements stored in the collection can only be specified in <> parentheses in the data type element;

The data type in the < data type > to store element must be a reference data type and cannot be 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

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

Let's take a few examples to clarify how a collection is created:

L Storing elements of type string

arraylist<string> list = new arraylist<string> ();

L Store data of type int

arraylist<integer> list = new arraylist<integer> ();

L Store phone-type data

arraylist<phone> list = new arraylist<phone> ();

Common methods for collections

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

Method declaration	Function description
Boolean add(int index, Object obj)	Inserts the specified element, obj , into the specified position in the collection
Object REM o ve(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

Java ArrayList Collection