Java Tutorial

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Java Loops

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Java Sorting

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Java OOPs Concepts

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Java Strings

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Java Exceptions

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Multithreading

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AWT

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Swing in Java

Java Collections

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Java Generics

Generics in Java

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Java JDBC

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How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to achieve abstraction in Java How to call static method in Java

Java 8 Features

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Java 9 Features

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Hibernate Tutorial

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Jenkins Tutorial

Java Math Methods

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Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

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Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java

ArrayList Program in Java

ArrayList Program in Java: In Java, ArrayList is a class that belongs to java.util package. It is the dynamic list that grows or shrinks at run-time as per the requirements. Because of its dynamic nature, an ArrayList is preferred over a primitive array. In other words, an ArrayList is the resizable array. The ArrayList class implements the List interface and inherits the AbstractList class.

Key Features of an ArrayList

The key features of an ArrayList are:

  • Duplicate elements are allowed in the ArrayList.
  • ArrayList maintains the insertion order of elements added to it.
  • ArrayList is not synchronized.
  • Like a primitive array, elements can be accessed randomly based on their index.

If we want to create an ArrayList, we need to create an instance of the ArrayList class.

ArrrayList<type> identifier = new ArrayList<type>();

In the above statement, identifier is the reference variable. Its name can be changed as per one’s choice. type in the angular brackets ensures what kind of array list is going to be created. For the creation of an integer list, Integer should be used inside the angular brackets. For the creation of a string list, String should be used, and so on.

FileName: ArrayListExample.java

 // Importing class ArrayList
import java.util.ArrayList;
public class ArrayListExample
{
// driver method
public static void main(String argvs[])
{
    // creating an array list of integer type
    ArrayList<Integer> al = new ArrayList<Integer>();
    // adding elements to the list
    al.add(1);
    al.add(-9);
    al.add(45);
    al.add(443);
    al.add(4);
    // calculating the size of the list
    int size = al.size();
    if(size > 0)
    {
        // displaying the size and the elements of the list
        System.out.println("Size of the array list is: " + size );
        System.out.println(al );
    }
}
} 

Output:

 Size of the array list is: 5
[1, -9, 45, 443, 4] 

Explanation: In the code, we have created an empty list. The add() method appends an element to the list. Thus, the add() method increases the size of the list by one. Eventually, we are printing the list on the console.

Iterating an ArrayList

There are many ways to iterate over an ArrayList.  A few of them are:

  • Using for-loop
  • Using an iterator

Let’s start with the for-loop.

Using For-Loop

Consider the following program.

FileName: ArrayListExample1.java

 // Importing class ArrayList
import java.util.ArrayList;
public class ArrayListExample1
{
// driver method
public static void main(String argvs[])
{
    // creating an array list of integer type
    ArrayList<Integer> al = new ArrayList<Integer>();
    // adding elements to the list
    al.add(1);
    al.add(-9);
    al.add(45);
    al.add(443);
    al.add(4);
    // calculating the size of the list
    int size = al.size();
    System.out.println("Elements of the array list are: " );
    // Iterating on every elements of the list
    for(int i = 0; i < size; i++)
    {
       System.out.println(al.get(i) );
    }
}
} 

Output:

 Elements of the array list are:
1
-9
45
443
4 

Explanation: After adding the elements to the list, we are calculating the size of the list. Then, using a Java for-loop, we are iterating over the elements of the lists. The get() method is used to access the elements of the list. It returns the element present at the given index. Thus, get(0) returns the element present at the index 0.  get(1) is responsible for accessing the element present at the index 1, and so on.

Using an Iterator

Consider the following program.

FileName: ArrayListExample2.java

 // Importing the class ArrayList
import java.util.ArrayList;
// Importing the class Iterator
import java.util.Iterator;
public class ArrayListExample2
{
// driver method
public static void main(String argvs[])
{
    // creating an array list of integer type
    ArrayList<Integer> al = new ArrayList<Integer>();
    // adding elements to the list
    al.add(1);
    al.add(-9);
    al.add(45);
    al.add(443);
    al.add(4);
    // calculating the size of the list
    int size = al.size();
    System.out.println("Elements of the array list are: " );
    // Creating an iterator for the list al
    Iterator itr = al.iterator();
    //check if the list has elements 
    while(itr.hasNext() )
    {  
        //printing the element and move to the next
        System.out.println(itr.next()); 
    }
}
}              

Output:

 Elements of the array list are:
1
-9
45
443
4 

Explanation: Instead of a for-loop, we have used an iterator to iterate the elements of the ArrayList. The hasNext() method checks elements are present in the list or not. If elements are presented in the ArrayList, it returns true, else returns false. The next() method returns the next element that is getting printed on the console.

Removing Elements from an ArrayList

To remove the elements from an ArrayList, the remove() method is used. Observe the following program.

FileName: ArrayListExample3.java

 // Importing the class ArrayList
import java.util.ArrayList;
// Importing the class Iterator
import java.util.Iterator;
public class ArrayListExample3
{
// driver method
public static void main(String argvs[])
{
    // creating an array list of integer type
    ArrayList<Integer> al = new ArrayList<Integer>();
    // adding elements to the list
    al.add(7);
    al.add(8);
    al.add(9);
    al.add(17);
    al.add(25);
    // removing the element present at the index 2
    al.remove(2);
    System.out.println("Elements of the array list are: " );
    // Creating an iterator for the list al
    Iterator itr = al.iterator();
    //check if iterator has the elements 
    while(itr.hasNext() )
    {  
        //printing the element and move to the next
        System.out.println(itr.next()); 
    }
}
} 

Output:

 Elements of the array list are:
7
8
17
25 

Explanation: Before the deletion of elements, the array list looked like the following.

ArrayList Program In Java

When the element at the 2nd index is deleted, the elements that followed element 9 get shifted towards the left by one place.

ArrayList Program In Java

Thus, the removal of an element from an array list is a lengthy process because shifting of elements from their original position takes time.



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