A regular Java array has a major downside: it can’t be resized. Sometimes you need an array that can dynamically change its size during runtime, and this is what ArrayList is for.

First, add ArrayList to your imports:

import java.util.ArrayList;

This is a generic declaration of an ArrayList:

ArrayList array = new ArrayList();

Where T is the desired type of the objects stored in the array, e.g. String. In the moment of declaration, the array stores no elements. The add() method, taking one T as a parameter, inserts a new element to the array’s tail.

ArrayList fruit = new ArrayList();

fruit.add(‘Apple’);

fruit.add(‘Orange’);

fruit.add(‘Banana’);

// [‘Apple’, ‘Orange’, ‘Banana’]

To interact with existing elements, get() and set() methods are used instead of the array operator []. Both methods expect a valid index, between 0 and n-1, where n is the current length of the ArrayList.

System.out.println(fruit.get(0)); // ‘Apple’

fruit.set(0, ‘Pear’);

System.out.println(fruit.get(0)); // ‘Pear’

Since the length of the array is dynamic, size() method is handy. For example, the following code iterates through every element:

for(int i = 0; i < fruit.size(); i++) {

    fruit.set(i, fruit.get(i) + ‘s’);

}

// [‘Pears’, ‘Oranges’, ‘Bananas’]

To find an element, use indexOf(). If no element is found, indexOf() returns -1.

int pos = fruit.indexOf(‘Bananas’);

// pos == 2

pos = fruit.indexOf(‘Carrots’);

// pos == -1

Lastly, remove() removes a specific element, and clear() empties the entire ArrayList:

fruit.remove(1);

// [‘Pears’, ‘Bananas’]

fruit.clear();

// []

The ArrayList can be copied to a regular array if needed. The copy is independent from the original ArrayList

String array[] = new String[fruit.size()];

array = fruit.toArray(array);

A full example:

import java.util.ArrayList;

public class ArrayListExample {

    public static void main(String[] args) {

        // Declaration

        ArrayList fruit = new ArrayList();

        // add()

        fruit.add(‘Apple’);

        fruit.add(‘Orange’);

        fruit.add(‘Banana’);

        System.out.println(fruit);

        // get() and set()

        System.out.println(fruit.get(0));

                fruit.set(0, ‘Pear’);

                System.out.println(fruit.get(0));

                // size()

                for(int i = 0; i < fruit.size(); i++) {

                    fruit.set(i, fruit.get(i) + ‘s’);

                }

                System.out.println(fruit);

                // indexOf()

                int pos = fruit.indexOf(‘Bananas’);

                System.out.println(‘Position of Bananas is ‘ + pos);

                pos = fruit.indexOf(‘Carrots’);

                System.out.println(‘Position of Carrots is ‘ + pos);

                // remove()

                fruit.remove(1);

                System.out.println(fruit);

                // clear()

                fruit.clear();

                System.out.println(fruit);

                // toArray()

                fruit.add(‘Lemon’);

        fruit.add(‘Raspberry’);

                String array[] = new String[fruit.size()];

                array = fruit.toArray(array);

                fruit.set(0, ‘Strawberry’);

                System.out.println(array[0]);

                System.out.println(fruit.get(0));

    }

}

How to Use ArrayList In Java

What is Arraylist in Java?

Array is a simple data structure that we use to store information about anything in programming languages, also ArrayList is class or data structure in Java that implement with List Interface and it based on Array data structure. It is very useful because of its functionality and flexibility in java. Developers preferred ArrayList Data Structure over Array because of its good functionalities. ArrayList provides all of its operations on it, add, delete etc.

How To Use ArrayList In Java with Example

            Java is giving us a facility for creating an array so first we want to import or add the java utility class that import all necessarily packages of java with our class. After that simple we declare an ArrayList. ArrayList may be String, int, Char, means primitive data types or may be user define objects. We can use ArrayList of Objects. Just we need to clarify when we declared the ArrayList. In the given example in we declare an arraylist of String type. Example is given below.

import java.util. * ;  

class ArrayList1 {  

    public static void main( String args [ ] ) {   

ArrayList < String > myList=new ArrayList< String >();  //Creating arraylist    

            list.add(‘Mr.’);

list.add(‘john’); //Adding object in arraylist    

            list.add(‘william’);    

            list.add(‘son’);    

                

            //Invoking arraylist object   

            System.out.println(myList);  

     }  

 }  

How To Use ArrayList In Java with Objects

We can use arraylist with objects.

ArrayList mylist = new ArrayList< Class Name >( ); //Creating an object array List 

Or  with an example

ArrayList < Matrices > mylist = new ArrayList < Matrices > ( ) ;

mylist.add( new Matrices( 1 , 1 , 10 ) ) ;

mylist.add( new Matrices ( 1 , 2 , 20 ) ) ;

Methods of Java ArrayList

ArrayList in java give us lot of facilities or functions those very helpful for using the array list. Some important and most useful functions and there description is given below.

There are also lot of build in functions available in java ArrayList you can see java documentation.

How To Use Arraylist In Java

Arraylist in java is a dynamic resizable array. It is present in the java.util package and is part of a collection framework, It implements the List Interface. We can store dynamically sized collection of elements in an Arraylist.

The main difference between Array and Arraylist in Java is that Arrays are fixed in size and cannot be increased. Whereas Arraylist can grow automatically when new elements are added.

Arraylist in Java are similar to vectors in C++.

Create a Arraylist

Insert Items into Arraylist

Get item at index

Change an item

Size of Arraylist

Loop Through each item

Sort the Arraylist

We will first need to import Collections class using

Delete an item

Check if Arraylist contains an item

Get index of element in Arraylist

Where do we use ArrayList in Java?

ArrayList in Java is used to store dynamically sized collection of elements. Contrary to Arrays that are fixed in size, an ArrayList grows its size automatically when new elements are added to it. ArrayList is part of Java’s collection framework and implements Java’s List interface.

What is ArrayList in Java with example?

Arraylist class implements List interface and it is based on an Array data structure. ArrayList is a resizable-array implementation of the List interface. It implements all optional list operations, and permits all elements, including null .

How do you create an ArrayList?

In Java, we can create ArrayList by creating this simple statement: ArrayList<String> arlist = new ArrayList<String>( ); In above syntax, list is of “String” type, so the elements are that going to be added to this list will be string type. The type decide which type of elements list will have.

How do you create an initial value in ArrayList?

Below are the various methods to initialize an ArrayList in Java:
  1. Initialization with add() Syntax: ArrayList<Type> str = new ArrayList<Type>(); str.add(“Geeks”); str.add(“for”); str.add(“Geeks”);
  2. Initialization using asList()
  3. Initialization using List.of() method.
  4. Initialization using another Collection.

What are the methods in ArrayList?

Methods of ArrayList
Method Description
void ensureCapacity(int requiredCapacity) It is used to enhance the capacity of an ArrayList instance.
E get(int index) It is used to fetch the element from the particular position of the list.
boolean isEmpty() It returns true if the list is empty, otherwise false.
Iterator()

Does ArrayList have size?

The size of an ArrayList can be obtained by using the java. size() method as it returns the number of elements in the ArrayList i.e. the size.

How do you call an ArrayList method?

So, first, make ArrayList as an instance variable to the PetList class so that it can be accessible through an object even outside the constructor. Then, you can provide an eatAll() method which iterates the ArrayList<Pet> and call the eat() method on all pet objects.

Does an ArrayList have a set size?

Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. As elements are added to an ArrayList, its capacity grows automatically. Also, for an ArrayList, size can not be set while initializing.

Can ArrayList increase size Java?

ArrayList is a resizable array implementation of the List interface i.e. ArrayList grows dynamically as the elements are added to it. But the size of the array can not be increased dynamically. So, what happens internally is, a new Array is created and the old array is copied into the new array.

What is difference between capacity and size of ArrayList?

An ArrayList object has a capacity and a size. The capacity is the total number of cells. The size is the number of cells that have data in them. Cells 0 up through size-1 have data in them.

What is the limit of ArrayList in Java?

2 Answers. ArrayList in Java has a get(int index) method. int is a signed 32 bit value, with a maximum value of 2,147,483,647. That is the largest possible value that can be accessed in an ArrayList .

What is the maximum size of an ArrayList?

The size limit of ArrayList is Integer. MAX_VALUE since it’s backed by an ordinary array.

What happens when ArrayList is full?

Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically.

Does ArrayList use a lot of memory?

So an ArrayList initialized with the default constructor, with only one element added, wastes either 36 or 72 bytes. In fact, an empty ArrayList wastes memory too, because it doesn’t carry any workload, yet the size of an ArrayList object itself is non-zero and bigger than you probably think.

How is ArrayList stored in memory?

The elements of an ArrayList are stored in a chunk of contiguous memory. When that memory becomes full, a larger chunk of contiguous memory has to be allocated (usually twice the size) and the existing elements are copied into this new chunk. We call this chunk the capacity of the ArrayList object.

How do you declare the size of an ArrayList?

Java. util. ArrayList. size() Method
  1. Description. The java. util.
  2. Declaration. Following is the declaration for java.util.ArrayList.size() method public int size()
  3. Parameters. NA.
  4. Return Value. This method returns the number of elements in this list.
  5. Exception. NA.
  6. Example. The following example shows the usage of java. util.

Is ArrayList thread safe?

Any method that touches the Vector ‘s contents is thread safe. ArrayList , on the other hand, is unsynchronized, making them, therefore, not thread safe. With that difference in mind, using synchronization will incur a performance hit. So if you don’t need a thread–safe collection, use the ArrayList .

How do you make an ArrayList thread safe?

A thread–safe variant of ArrayList in which all mutative operations (e.g. add, set, remove..) are implemented by creating a separate copy of underlying array. It achieves thread–safety by creating a separate copy of List which is a is different way than vector or other collections use to provide thread–safety.