Java API ArrayList Example

Java API ArrayList Overview

In this tutorial, We'll learn about Java Collection API ArrayList.
ArrayList is a class which is widely used in real time applications. It is in package java.util and public class. This is added in java 1.2 version.

Class Name: ArrayList
First Version: 1.2
Super Class: AbstractList
Implemented interfaces: List, RandomAccess, Cloneable, Serializable
Pacakge: java.util.

Class Signature

public class ArrayList extends AbstractList implements List, RandomAccess, Cloneable, Serializable

Class - AbstractList

Interfaces - List, RandomAccess, Cloneable, Serializable

ArrayList Characteristics

1) Implemented based on resizable array.
2) Allows null values.
3) Allows duplicate values.
4) Provides random access, we can access any positioned element because works on index based.
5) Allows primitives, wrapper classes and user defined classes.
6) Maintains insertion order.
7) Non-Synchronized
8) Similar to Vector but Vector is synchronized.
9) It is a built in data structure in java.
10) Slower when inserts elements in middle because all are needs to shifted
11) Provides many utility methods support to get size, add elements, get or remove elements.

ArrayList Constructors

It has three constructors.

ArrayList() : Which is a default and Constructs an empty list with an initial capacity of ten.
ArrayList(Collection<? extends E> c) : Constructs a list containing the elements of the specified collection.
ArrayList(int initialCapacity) : Constructs an empty list with the specified initial capacity.

ArrayList Methods

boolean add(E e) : Appends the specified element to the end of this list.
void add(int index, E element) : Inserts the specified element at the specified position in this list.
boolean addAll(Collection c) : Appends all of the elements in the specified collection to the end of this list.
void clear() : Removes all of the elements from this list.
boolean contains(Object o) : Returns true if this list contains the specified element.
E get(int index) : Returns the element at the specified position in this list.
int indexOf(Object o) : Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
boolean isEmpty() : Returns true if this list contains no elements.
Iterator<E> iterator() : Returns an iterator over the elements in this list in proper sequence.
E remove(int index) : Removes the element at the specified position in this list.
boolean remove(Object o) : Removes the first occurrence of the specified element from this list, if it is present.
boolean removeAll(Collection c) : Removes from this list all of its elements that are contained in the specified collection.
int size() : Returns the number of elements in this list.


More about Boxing and Unboxing in java.

What is the default size of the ArrayList?

Default size is 10.

ArrayList Example

In this example, we will see

1) how to create object for ArrayList?
2) How to add elements?
3) How to print elements?

package com.java.w3schools.arraylist;
import java.util.ArrayList;
import java.util.List;
public class ArrayListExample {
    public static void main(String[] args) {
        // Creating ArrayList object.
        List fruits = new ArrayList<>();
        // Adding elements
        fruits.add("apple");
        fruits.add("Banana");
        fruits.add("Cherries");
        // printing elements
        for (String value : fruits) {
            System.out.println("fruit name : " + value);
        }
    }
}

Output:

fruit name : apple
fruit name : Banana
fruit name : Cherries

More about Iterating ArrayList using Enhanced For Loop.

Conclusion

In this tutorial, We've seen What is ArrayList and How to Create ArrayList Object.

What are the characteristics of ArrayList ?

Methods of ArrayList with basic example program.