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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:

Learn java - java tutorial - arraylist - java examples - java programs

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

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

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

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 collection. Now it is type safe so typecasting is not required at run time. 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  

import java.util.*;  
public class TestCollection1{  
 public static void main(String args[]){  
  ArrayList<String> list=new ArrayList<String>();//Creating arraylist  
  list.add("Raji");//Adding object in arraylist  
  list.add("Vijay");  
  list.add("Raju");  
  list.add("Ajith");  
  //Traversing list through Iterator  
  Iterator itr=list.iterator();  
  while(itr.hasNext()){  
   System.out.println(itr.next());  
  }  
 }  
}  

 Raji
 Vijay
       Raju
       Ajith

There are two ways to traverse collection elements:

In the above example, we have seen traversing ArrayList by Iterator. Let's see the example to traverse ArrayList elements using for-each loop

import java.util.*;  
public class TestCollection2{  
 public static void main(String args[]){  
  ArrayList<String> al=new ArrayList<String>();  
  al.add("Raji");  
  al.add("Vijay");  
  al.add("Raju");  
  al.add("Ajith");  
  for(String obj:al)  
    System.out.println(obj);  
 }  
}  

  Raji
 Vijay
       Raju
       Ajith

Let's see an example where we are storing Student class object in 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.*;  
public public class TestCollection3{  
 public static void main(String args[]){  
  //Creating user-defined class objects  
  Student s1=new Student(101,"Sonu",23);  
  Student s2=new Student(102,"Raja",21);  
  Student s2=new Student(103,"anu",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 Sonu 23
       102 Raja 21
       103 anu 25

import java.util.*;  
public class TestCollection4{  
 public static void main(String args[]){  
  ArrayList<String> al=new ArrayList<String>();  
  al.add("Ravi");  
  al.add("jay");  
  al.add("Ajay");  
  ArrayList<String> al2=new ArrayList<String>();  
  al2.add("Sonu");  
  al2.add("anu");  
  al.addAll(al2);//adding second list in first list  
  Iterator itr=al.iterator();  
  while(itr.hasNext()){  
   System.out.println(itr.next());  
  }  
 }  
}  

Ravi
       jay
       Ajay
       Sonu
       anu

import java.util.*;  
public class TestCollection5{  
 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("Raji");  
  al2.add("anu");  
  al.removeAll(al2);  
  System.out.println("iterating the elements after removing the elements of al2...");  
  Iterator itr=al.iterator();  
  while(itr.hasNext()){  
   System.out.println(itr.next());  
  }  
  
  }  
}  

iterating the elements after removing the elements of al2...
       Vijay
       Ajay

import java.util.*;  
public class TestCollection6{  
 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("Raji");  
  al2.add("anu");  
  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...
       Raji

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

import java.util.*;  
public 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","BPB",8);  
    Book b2=new Book(102,"Data Communications ","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);  
    }  
}  
}  

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