Java Code Guru Ji (8920128728): Java ArrayList class

Java ArrayList class uses a dynamic array for storing the elements. It inherits AbstractList class and implements List interface.

The important points about Java ArrayList class are:

Java ArrayList class can contain duplicate elements.
Java ArrayList class maintains insertion order.
Java ArrayList class is non synchronized.
Java ArrayList allows random access because array works at the index basis.
In Java ArrayList class, manipulation is slow because a lot of shifting needs to occur if any element is removed from the array list.

Hierarchy of ArrayList class

As shown in the above diagram, Java ArrayList class extends AbstractList class which implements List interface. The List interface extends Collection and Iterable interfaces in hierarchical order.

ArrayList class declaration

Let's see the declaration for java.util.ArrayList class.

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, Serializable

Constructors of Java ArrayList

Constructor	Description
ArrayList()	It is used to build an empty array list.
ArrayList(Collection<? extends E> c)	It is used to build an array list that is initialized with the elements of the collection c.
ArrayList(int capacity)	It is used to build an array list that has the specified initial capacity.

Methods of Java ArrayList

Method	Description
void add(int index, E element)	It is used to insert the specified element at the specified position in a list.
boolean add(E e)	It is used to append the specified element at the end of a list.
boolean addAll(Collection<? extends E> c)	It is used to append all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator.
boolean addAll(int index, Collection<? extends E> c)	It is used to append all the elements in the specified collection, starting at the specified position of the list.
void clear()	It is used to remove all of the elements from this list.
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.
int lastIndexOf(Object o)	It is used to return the index in this list of the last occurrence of the specified element, or -1 if the list does not contain this element.
Object[] toArray()	It is used to return an array containing all of the elements in this list in the correct order.
<T> T[] toArray(T[] a)	It is used to return an array containing all of the elements in this list in the correct order.
Object clone()	It is used to return a shallow copy of an ArrayList.
boolean contains(Object o)	It returns true if the list contains the specified element
int indexOf(Object o)	It is used to return the index in this list of the first occurrence of the specified element, or -1 if the List does not contain this element.
E remove(int index)	It is used to remove the element present at the specified position in the list.
boolean remove(Object o)	It is used to remove the first occurrence of the specified element.
boolean removeAll(Collection<?> c)	It is used to remove all the elements from the list.
boolean removeIf(Predicate<? super E> filter)	It is used to remove all the elements from the list that satisfies the given predicate.
protected void removeRange(int fromIndex, int toIndex)	It is used to remove all the elements lies within the given range.
void replaceAll(UnaryOperator<E> operator)	It is used to replace all the elements from the list with the specified element.
void retainAll(Collection<?> c)	It is used to retain all the elements in the list that are present in the specified collection.
E set(int index, E element)	It is used to replace the specified element in the list, present at the specified position.
void sort(Comparator<? super E> c)	It is used to sort the elements of the list on the basis of specified comparator.
Spliterator<E> spliterator()	It is used to create spliterator over the elements in a list.
List<E> subList(int fromIndex, int toIndex)	It is used to fetch all the elements lies within the given range.
int size()	It is used to return the number of elements present in the list.
void trimToSize()	It is used to trim the capacity of this ArrayList instance to be the list's current size.

Java Non-generic Vs. Generic Collection

Java collection framework was non-generic before JDK 1.5. Since 1.5, it is generic.

Java new generic collection allows you to have only one type of object in a collection. Now it is type safe so typecasting is not required at runtime.

Let's see the old non-generic example of creating java collection.

ArrayList al=new ArrayList();//creating old non-generic arraylist

Let's see the new generic example of creating java collection.

ArrayList<String> al=new ArrayList<String>();//creating new generic arraylist

In a generic collection, we specify the type in angular braces. Now ArrayList is forced to have the only specified type of objects in it. If you try to add another type of object, it gives compile time error.

For more information on Java generics, click here Java Generics Tutorial.

Java ArrayList Example

import java.util.*;
class ArrayList1{
public static void main(String args[]){
ArrayList<String> list=new ArrayList<String>();//Creating arraylist
list.add("Ravi");//Adding object in arraylist
list.add("Vijay");
list.add("Ravi");
list.add("Ajay");
//Invoking arraylist object
System.out.println(list);
}
}
}

       [Ravi, Vijay, Ravi, Ajay]

Ways to iterate the elements of the collection in java

There are various ways to traverse the collection elements:

By Iterator interface.
By for-each loop.
By ListIterator interface.
By for loop.
By forEach() method.
By forEachRemaining() method.

Iterating Collection through Iterator interface

Let's see an example to traverse ArrayList elements using the Iterator interface.

import java.util.*;
class ArrayList2{
public static void main(String args[]){
ArrayList<String> list=new ArrayList<String>();//Creating arraylist
list.add("Ravi");//Adding object in arraylist
list.add("Vijay");
list.add("Ravi");
list.add("Ajay");
//Traversing list through Iterator
Iterator itr=list.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}

       Ravi
       Vijay
       Ravi
       Ajay

Iterating Collection through the for-each loop

Let's see an example to traverse the ArrayList elements using the for-each loop

import java.util.*;
class ArrayList3{
public static void main(String args[]){
ArrayList<String> al=new ArrayList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
//Traversing list through for-each loop
for(String obj:al)
System.out.println(obj);
}
}

       Ravi
       Vijay
       Ravi
       Ajay

Iterating Collection through remaining ways

Let's see an example to traverse the ArrayList elements through other ways

import java.util.*;
class ArrayList4{
public static void main(String args[]){
ArrayList<String> list=new ArrayList<String>();//Creating arraylist
list.add("Ravi");//Adding object in arraylist
list.add("Vijay");
list.add("Ravi");
list.add("Ajay");
System.out.println("Traversing list through List Iterator:");
//Here, element iterates in reverse order
ListIterator<String> list1=list.listIterator(list.size());
while(list1.hasPrevious())
{
String str=list1.previous();
System.out.println(str);
}
System.out.println("Traversing list through for loop:");
for(int i=0;i<list.size();i++)
{
System.out.println(list.get(i));
}
System.out.println("Traversing list through forEach() method:");
//The forEach() method is a new feature, introduced in Java 8.
list.forEach(a->{ //Here, we are using lambda expression
System.out.println(a);
});
System.out.println("Traversing list through forEachRemaining() method:");
Iterator<String> itr=list.iterator();
itr.forEachRemaining(a-> //Here, we are using lambda expression
{
System.out.println(a);
});
}
}

Traversing list through List Iterator:
Ajay
Ravi
Vijay
Ravi
Traversing list through for loop:
Ravi
Vijay
Ravi
Ajay
Traversing list through forEach() method:
Ravi
Vijay
Ravi
Ajay
Traversing list through forEachRemaining() method:
Ravi
Vijay
Ravi
Ajay

User-defined class objects in Java ArrayList

Let's see an example where we are storing Student class object in an array list.

class Student{
int rollno;
String name;
int age;
Student(int rollno,String name,int age){
this.rollno=rollno;
this.name=name;
this.age=age;
}
}

import java.util.*;
class ArrayList5{
public static void main(String args[]){
//Creating user-defined class objects
Student s1=new Student(101,"Sonoo",23);
Student s2=new Student(102,"Ravi",21);
Student s2=new Student(103,"Hanumat",25);
//creating arraylist
ArrayList<Student> al=new ArrayList<Student>();
al.add(s1);//adding Student class object
al.add(s2);
al.add(s3);
//Getting Iterator
Iterator itr=al.iterator();
//traversing elements of ArrayList object
while(itr.hasNext()){
Student st=(Student)itr.next();
System.out.println(st.rollno+" "+st.name+" "+st.age);
}
}
}

       101 Sonoo 23
       102 Ravi 21
       103 Hanumat 25

Java ArrayList Serialization and Deserialization Example

Let's see an example to serialize an ArrayList object and then deserialize it.

import java.io.*;
import java.util.*;
class ArrayList6 {
public static void main(String [] args)
{
ArrayList<String> al=new ArrayList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ajay");
try
{
//Serialization
FileOutputStream fos=new FileOutputStream("file");
ObjectOutputStream oos=new ObjectOutputStream(fos);
oos.writeObject(al);
fos.close();
oos.close();
//Deserialization
FileInputStream fis=new FileInputStream("file");
ObjectInputStream ois=new ObjectInputStream(fis);
ArrayList list=(ArrayList)ois.readObject();
System.out.println(list);
}catch(Exception e)
{
System.out.println(e);
}
}
}

       [Ravi, Vijay, Ajay]

Java ArrayList example to add elements

Here, we see different ways to add an element.

import java.util.*;
class ArrayList7{
public static void main(String args[]){
ArrayList<String> al=new ArrayList<String>();
System.out.println("Initial list of elements: "+al);
//Adding elements to the end of the list
al.add("Ravi");
al.add("Vijay");
al.add("Ajay");
System.out.println("After invoking add(E e) method: "+al);
//Adding an element at the specific position
al.add(1, "Gaurav");
System.out.println("After invoking add(int index, E element) method: "+al);
ArrayList<String> al2=new ArrayList<String>();
al2.add("Sonoo");
al2.add("Hanumat");
//Adding second list elements to the first list
al.addAll(al2);
System.out.println("After invoking addAll(Collection<? extends E> c) method: "+al);
ArrayList<String> al3=new ArrayList<String>();
al3.add("John");
al3.add("Rahul");
//Adding second list elements to the first list at specific position
al.addAll(1, al3);
System.out.println("After invoking addAll(int index, Collection<? extends E> c) method: "+al);
}
}

Initial list of elements: []
After invoking add(E e) method: [Ravi, Vijay, Ajay]
After invoking add(int index, E element) method: [Ravi, Gaurav, Vijay, Ajay]
After invoking addAll(Collection<? extends E> c) method: 
[Ravi, Gaurav, Vijay, Ajay, Sonoo, Hanumat]
After invoking addAll(int index, Collection<? extends E> c) method: 
[Ravi, John, Rahul, Gaurav, Vijay, Ajay, Sonoo, Hanumat]

Java ArrayList example to remove elements

Here, we see different ways to remove an element.

import java.util.*;
class ArrayList8 {
public static void main(String [] args)
{
ArrayList<String> al=new ArrayList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ajay");
al.add("Anuj");
al.add("Gaurav");
System.out.println("An initial list of elements: "+al);
//Removing specific element from arraylist
al.remove("Vijay");
System.out.println("After invoking remove(object) method: "+al);
//Removing element on the basis of specific position
al.remove(0);
System.out.println("After invoking remove(index) method: "+al);
//Creating another arraylist
ArrayList<String> al2=new ArrayList<String>();
al2.add("Ravi");
al2.add("Hanumat");
//Adding new elements to arraylist
al.addAll(al2);
System.out.println("Updated list : "+al);
//Removing all the new elements from arraylist
al.removeAll(al2);
System.out.println("After invoking removeAll() method: "+al);
//Removing elements on the basis of specified condition
al.removeIf(str -> str.contains("Ajay")); //Here, we are using Lambda expression
System.out.println("After invoking removeIf() method: "+al);
//Removing all the elements available in the list
al.clear();
System.out.println("After invoking clear() method: "+al);
}
}

An initial list of elements: [Ravi, Vijay, Ajay, Anuj, Gaurav]
After invoking remove(object) method: [Ravi, Ajay, Anuj, Gaurav]
After invoking remove(index) method: [Ajay, Anuj, Gaurav]
Updated list : [Ajay, Anuj, Gaurav, Ravi, Hanumat]
After invoking removeAll() method: [Ajay, Anuj, Gaurav]
After invoking removeIf() method: [Anuj, Gaurav]
After invoking clear() method: []

Java ArrayList example of retainAll() method

import java.util.*;
class ArrayList9{
public static void main(String args[]){
ArrayList<String> al=new ArrayList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ajay");
ArrayList<String> al2=new ArrayList<String>();
al2.add("Ravi");
al2.add("Hanumat");
al.retainAll(al2);
System.out.println("iterating the elements after retaining the elements of al2");
Iterator itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}

       iterating the elements after retaining the elements of al2
       Ravi

Java ArrayList example of isEmpty() method

import java.util.*;
class ArrayList10{
public static void main(String [] args)
{
ArrayList<String> al=new ArrayList<String>();
System.out.println("Is ArrayList Empty: "+al.isEmpty());
al.add("Ravi");
al.add("Vijay");
al.add("Ajay");
System.out.println("After Insertion");
System.out.println("Is ArrayList Empty: "+al.isEmpty());
}
}

Is ArrayList Empty: true
After Insertion
Is ArrayList Empty: false

Java ArrayList example of set() and get() method

import java.util.*;
class ArrayList11 {
public static void main(String [] args)
{
ArrayList<String> al=new ArrayList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ajay");
System.out.println("Before update: "+al.get(1));
//Updating an element at specific position
al.set(1,"Gaurav");
System.out.println("After update: "+al.get(1));
}
}

Before update: Vijay
After update: Gaurav

Java ArrayList Example: Book

Let's see an ArrayList example where we are adding books to list and printing all the books.

import java.util.*;
class Book {
int id;
String name,author,publisher;
int quantity;
public Book(int id, String name, String author, String publisher, int quantity) {
this.id = id;
this.name = name;
this.author = author;
this.publisher = publisher;
this.quantity = quantity;
}
}
public class ArrayListExample {
public static void main(String[] args) {
//Creating list of Books
List<Book> list=new ArrayList<Book>();
//Creating Books
Book b1=new Book(101,"Let us C","Yashwant Kanetkar","BPB",8);
Book b2=new Book(102,"Data Communications & Networking","Forouzan","Mc Graw Hill",4);
Book b3=new Book(103,"Operating System","Galvin","Wiley",6);
//Adding Books to list
list.add(b1);
list.add(b2);
list.add(b3);
//Traversing list
for(Book b:list){
System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity);
}
}
}

Output:

101 Let us C Yashwant Kanetkar BPB 8
102 Data Communications & Networking Forouzan Mc Graw Hill 4
103 Operating System Galvin Wiley 6

Java Code Guru Ji (8920128728)

Sunday, September 15, 2019

Java ArrayList class