ArrayList in Java

 

🧭 ArrayList in Java

In Java, an ArrayList is a dynamic array that can grow and shrink in size during program execution.

Unlike normal arrays (which have a fixed size), an ArrayList provides flexibility and powerful built-in methods to store, access, and manage data efficiently.

ArrayList is one of the most widely used classes in the Java Collections Framework.

🔹 What is an ArrayList?

An ArrayList in Java is a resizable array that can hold objects. It automatically increases its capacity when elements are added beyond its current size.

It belongs to the package:

java.util

ArrayList can store duplicate elements, maintains insertion order, and allows random access using indexes.

🔹 Syntax to Create an ArrayList

ArrayList<Type> listName = new ArrayList<Type>();

Example:

import java.util.ArrayList;

public class Example {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<Integer>();
    }
}

🔹 Key Features of ArrayList

✅ Dynamic size – Grows or shrinks automatically
✅ Maintains insertion order
✅ Allows duplicate elements
✅ Provides random access using indexes
✅ Not synchronized – faster but not thread-safe
✅ Part of Java Collections Framework

🔹 Adding Elements to an ArrayList

You can add elements using the add() method.

import java.util.ArrayList;

public class AddExample {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<String>();

        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");

        System.out.println("Fruits: " + fruits);
    }
}

Output:

Fruits: [Apple, Banana, Cherry]

🔹 Accessing Elements in an ArrayList

You can use the get(index) method to access elements.

System.out.println(fruits.get(1)); // prints Banana

Or loop through all elements:

for (int i = 0; i < fruits.size(); i++) {
    System.out.println(fruits.get(i));
}

🔹 Updating and Removing Elements

Update:

fruits.set(1, "Blueberry");
System.out.println(fruits);

Output:

[Apple, Blueberry, Cherry]

Remove:

fruits.remove(2);
System.out.println(fruits);

Output:

[Apple, Blueberry]

🔹 Example 1: Basic ArrayList Operations

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<Integer>();

        // Adding elements
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        numbers.add(40);

        System.out.println("Initial ArrayList: " + numbers);

        // Accessing elements
        System.out.println("First element: " + numbers.get(0));

        // Updating element
        numbers.set(2, 99);
        System.out.println("After update: " + numbers);

        // Removing element
        numbers.remove(1);
        System.out.println("After removal: " + numbers);
    }
}

Output:

Initial ArrayList: [10, 20, 30, 40]
First element: 10
After update: [10, 20, 99, 40]
After removal: [10, 99, 40]

🔹 Iterating Through an ArrayList

You can traverse an ArrayList using:

1️⃣ For Loop

for (int i = 0; i < numbers.size(); i++) {
    System.out.println(numbers.get(i));
}

2️⃣ Enhanced For Loop

for (int n : numbers) {
    System.out.println(n);
}

3️⃣ Iterator

import java.util.Iterator;

Iterator<Integer> it = numbers.iterator();
while (it.hasNext()) {
    System.out.println(it.next());
}

🔹 Common ArrayList Methods

MethodDescriptionExample
add(element)    Adds an element    list.add(10)
add(index, element)    Adds at a specific position    list.add(1, 25)
get(index)    Returns element    list.get(2)
set(index, element)    Replaces element    list.set(0, 99)
remove(index)    Removes element    list.remove(1)
clear()    Removes all elements    list.clear()
size()    Returns number of elements    list.size()
contains(value)    Checks if value exists    list.contains(30)
isEmpty()    Checks if list is empty    list.isEmpty()

🔹 Example 2: Using ArrayList Methods

import java.util.ArrayList;

public class ArrayListMethods {
    public static void main(String[] args) {
        ArrayList<String> animals = new ArrayList<String>();

        animals.add("Dog");
        animals.add("Cat");
        animals.add("Elephant");
        animals.add("Tiger");

        System.out.println("Animals: " + animals);
        System.out.println("First: " + animals.get(0));
        System.out.println("Contains Cat? " + animals.contains("Cat"));
        System.out.println("Size: " + animals.size());

        animals.remove("Cat");
        System.out.println("After removing Cat: " + animals);
    }
}

Output:

Animals: [Dog, Cat, Elephant, Tiger]
First: Dog
Contains Cat? true
Size: 4
After removing Cat: [Dog, Elephant, Tiger]

🔹 ArrayList vs Vector

FeatureArrayListVector
Synchronization        ❌ Not synchronized        ✅ Synchronized
Performance        ⚡ Faster        ⚙️ Slower
Growth rate        Increases by 50%        Doubles in size
Introduced in        JDK 1.2        JDK 1.0
Use case        Single-threaded programs        Multi-threaded programs

🔹 Example 3: Copy All Elements from One ArrayList to Another

import java.util.ArrayList;

public class CopyArrayList {
    public static void main(String[] args) {
        ArrayList<String> list1 = new ArrayList<String>();
        list1.add("Red");
        list1.add("Green");
        list1.add("Blue");

        ArrayList<String> list2 = new ArrayList<String>();
        list2.addAll(list1);

        System.out.println("List 1: " + list1);
        System.out.println("List 2: " + list2);
    }
}

Output:

List 1: [Red, Green, Blue]
List 2: [Red, Green, Blue]

🔹 Example 4: Sorting Elements in an ArrayList

import java.util.ArrayList;
import java.util.Collections;

public class SortArrayList {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<Integer>();

        numbers.add(45);
        numbers.add(10);
        numbers.add(67);
        numbers.add(32);

        System.out.println("Before Sorting: " + numbers);

        // Sorting in ascending order
        Collections.sort(numbers);
        System.out.println("After Sorting: " + numbers);
    }
}

Output:

Before Sorting: [45, 10, 67, 32]
After Sorting: [10, 32, 45, 67]

🔹 Example 5: Searching for an Element in an ArrayList

import java.util.ArrayList;
import java.util.Scanner;

public class SearchElement {
    public static void main(String[] args) {
        ArrayList<String> cities = new ArrayList<String>();
        Scanner sc = new Scanner(System.in);

        cities.add("Kochi");
        cities.add("Chennai");
        cities.add("Bangalore");
        cities.add("Delhi");

        System.out.println("Cities: " + cities);
        System.out.print("Enter a city to search: ");
        String name = sc.nextLine();

        if (cities.contains(name)) {
            System.out.println(name + " is present in the list!");
        } else {
            System.out.println(name + " is not found in the list!");
        }

        sc.close();
    }
}

Output:

Cities: [Kochi, Chennai, Bangalore, Delhi]
Enter a city to search: Bangalore
Bangalore is present in the list!

💡 Summary

ConceptDescription
ArrayList            Dynamic array in Java
Resizable            Grows automatically as elements are added
Not synchronized            Faster than Vector
Common methods       add(), get(), set(), remove(), size()
Belongs to       java.util package

🧾 Key Takeaway

The ArrayList is one of the most important and flexible data structures in Java.
It provides the efficiency of arrays combined with the dynamic behavior of linked structures — making it ideal for most modern Java applications.

Example Programs

 1️⃣ Create an ArrayList of 5 Numbers and Find Their Average

import java.util.ArrayList;

public class AverageArrayList {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<Integer>();

        // Adding 5 numbers
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        numbers.add(40);
        numbers.add(50);

        int sum = 0;

        // Calculate sum of all elements
        for (int n : numbers) {
            sum += n;
        }

        double average = (double) sum / numbers.size();

        System.out.println("Numbers: " + numbers);
        System.out.println("Average = " + average);
    }
}

Output:

Numbers: [10, 20, 30, 40, 50]
Average = 30.0

2️⃣ Write a Program to Remove Duplicate Elements from an ArrayList

import java.util.ArrayList;

public class RemoveDuplicates {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<Integer>();

        // Add elements (with duplicates)
        numbers.add(10);
        numbers.add(20);
        numbers.add(10);
        numbers.add(30);
        numbers.add(20);

        System.out.println("Original List: " + numbers);

        // Create a new list to store unique elements
        ArrayList<Integer> unique = new ArrayList<Integer>();

        for (int n : numbers) {
            if (!unique.contains(n)) {
                unique.add(n);
            }
        }

        System.out.println("List after removing duplicates: " + unique);
    }
}

Output:

Original List: [10, 20, 10, 30, 20]
List after removing duplicates: [10, 20, 30]

3️⃣ Write a Program to Reverse an ArrayList

import java.util.ArrayList;
import java.util.Collections;

public class ReverseArrayList {
    public static void main(String[] args) {
        ArrayList<String> colors = new ArrayList<String>();

        colors.add("Red");
        colors.add("Green");
        colors.add("Blue");
        colors.add("Yellow");

        System.out.println("Original List: " + colors);

        // Reverse the ArrayList
        Collections.reverse(colors);

        System.out.println("Reversed List: " + colors);
    }
}

Output:

Original List: [Red, Green, Blue, Yellow]
Reversed List: [Yellow, Blue, Green, Red]

 4️⃣ Create an ArrayList of Strings and Find the Longest String

import java.util.ArrayList;

public class LongestString {
    public static void main(String[] args) {
        ArrayList<String> words = new ArrayList<String>();

        words.add("Apple");
        words.add("Banana");
        words.add("Cherry");
        words.add("Pineapple");
        words.add("Mango");

        System.out.println("Words: " + words);

        String longest = words.get(0);

        for (String w : words) {
            if (w.length() > longest.length()) {
                longest = w;
            }
        }

        System.out.println("Longest word: " + longest);
    }
}

Output:

Words: [Apple, Banana, Cherry, Pineapple, Mango]
Longest word: Pineapple

5️⃣ Write a Program to Merge Two ArrayLists and Display the Result

import java.util.ArrayList;

public class MergeArrayLists {
    public static void main(String[] args) {
        ArrayList<String> list1 = new ArrayList<String>();
        list1.add("A");
        list1.add("B");
        list1.add("C");

        ArrayList<String> list2 = new ArrayList<String>();
        list2.add("D");
        list2.add("E");
        list2.add("F");

        System.out.println("List 1: " + list1);
        System.out.println("List 2: " + list2);

        // Merge both lists
        ArrayList<String> mergedList = new ArrayList<String>();
        mergedList.addAll(list1);
        mergedList.addAll(list2);

        System.out.println("Merged List: " + mergedList);
    }
}

Output:

List 1: [A, B, C]
List 2: [D, E, F]
Merged List: [A, B, C, D, E, F]


Comments

Post a Comment

Popular posts from this blog

Object Oriented Programming PBCST304 KTU BTech CS Semester 3 2024 Scheme - Dr Binu V P

 About Me Course Details and Syllabus This course is a Project Based Learning  ( PBL) Course - know more PBCST304 Object Oriented Programming Model Question Paper and Answers Programs to Try Module-1  Introduction to Java Introduction - basic Java Program Java Compiler and Java Virtual Machine Java Command line and IDE Primitive data types and wrapper classes-autoboxing and unboxing Type casting Operators in Java Operator Precedence Control Statements in Java Example Programs using control statements Arrays in Java Strings in Java Vectors in Java ArrayList in Java Functions in Java Recursive Functions in Java Command Line arguments and Variable length arguments OOPs concept Procedural and Object Oriented Programming Paradigms Classes , objects and constructor in Java Access Modifiers in Java this keyword in Java Data Abstraction and Encapsulation Inheritance and Polymorphism Module-2 Method overloading in Java Object as parameters and Returning Objects Static members Fina...
Read more

Introduction to Java Programming

  🔰 Introduction to Java Programming Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle Corporation ). It is widely used for building applications across platforms — from desktop to mobile to enterprise systems. ✨ Key Features of Java: Platform Independent : "Write once, run anywhere" — Java code runs on any device with the Java Virtual Machine (JVM). Object-Oriented : Everything in Java is an object; this promotes reusability and modularity. Simple and Familiar : Syntax is similar to C/C++, making it easier for students with prior programming exposure. Secure : Java includes built-in security features like bytecode verification. Robust : Strong memory management and exception handling. Multithreaded : Supports concurrent execution of two or more threads. ✅ Structure of a Java Program public class HelloWorld { public static void main (String[] args) { System.out.println( ...
Read more

Inheritance and Polymorphism

Let's dive deep into Inheritance and Polymorphism , two fundamental pillars of Object-Oriented Programming (OOP) in Java. 🔷 INHERITANCE in Java 📌 Definition: Inheritance is the mechanism in Java by which one class acquires the properties and behaviors (fields and methods) of another class. The class that inherits is called the subclass (or child class). The class from which it inherits is the superclass (or parent class). ✅ Syntax: class SuperClass { // fields and methods } class SubClass extends SuperClass { // additional fields and methods }  Example: class Animal { void eat () { System.out.println( "This animal eats food." ); } } class Dog extends Animal { void bark () { System.out.println( "The dog barks." ); } } public class Main { public static void main (String[] args) { Dog d = new Dog (); d.eat(); // Inherited method d.bark(); ...
Read more