Difference between Anonymous Inner Class and Lambda Expression : A Comprehensive Guide 2208

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Difference between Anonymous Inner Class and Lambda Expression


In the dynamic realm of Java programming, two powerful constructs, Anonymous Inner Classes, and Lambda Expressions, stand out for their ability to enhance code flexibility. Both serve the purpose of implementing functional interfaces, but they differ significantly in their syntax, use cases, and behavior. Let’s delve into a detailed comparison to uncover the distinctions between these two essential features.

Anonymous Inner Class: A Closer Look

Definition and Purpose: An Anonymous Inner Class is essentially an inner class without a name, instantiated at the point of creation. It shines when you need a one-time-use class, particularly when overloading methods of a class or interface is necessary without the need to create a dedicated subclass.

Use Cases:

  • Creating implementation classes for listener interfaces, often employed in graphics programming.
  • Instantiating an object with added functionalities, especially when subclassing seems impractical.


Test t = new Test() {
   // Data members and methods
   public void test_method() {
      // Implementation


interface Age {
    int x = 21;
    void getAge();

class AnonymousDemo {
    public static void main(String[] args) {
        Age obj = new Age() {
            public void getAge() {
                System.out.print("Age is " + x);


Age is 21


  1. Can extend abstract and concrete classes.
  2. Allows the implementation of interfaces with any number of abstract methods.
  3. Can declare instance variables.

Memory and Compilation:

  • Generates a separate .class file at compile time.
  • Memory allocation occurs on-demand when creating an object.

Lambda Expressions: Embracing Conciseness

Definition and Purpose: Lambda Expressions, introduced in Java 8, are concise and expressive representations of instances of functional interfaces. They facilitate treating functionality as a method argument and bring a functional programming paradigm to Java.

Use Cases:

  • Implement a functional interface using a single abstract method.
  • Simplifying code, especially in scenarios involving event listeners.


FuncInterface fobj = (int x) -> System.out.println(2 * x);


interface FuncInterface {
    void abstractFun(int x);

    default void normalFun() {

class Test {
    public static void main(String args[]) {
        FuncInterface fobj = (int x) -> System.out.println(2 * x);




  1. Cannot extend abstract or concrete classes.
  2. Limited to implementing interfaces with a single abstract method.
  3. Does not allow the declaration of instance variables; variables act as local variables.

Memory and Compilation:

  • No separate .class file generated at compile time.
  • Resides in the permanent memory of the JVM.

Table of Difference:

FeatureAnonymous Inner ClassLambda Expression
NatureClass without a nameMethod without a name (anonymous function)
InheritanceCan extend abstract and concrete classesCannot extend abstract or concrete classes
Interface ImplementationCan implement an interface with any methodsCan implement an interface with a single method
Variable DeclarationAllows declaration of instance variablesNo instance variable declaration allowed
InstantiationCan be instantiatedCannot be instantiated
“this” ReferenceRefers to the current anonymous class objectRefers to the current outer class object
Handling MethodsSuitable for handling multiple methodsBest choice for handling a single interface method
Compilation OutputGenerates a separate .class fileNo separate .class file generated
Memory AllocationOn-demand when creating an objectResides in permanent memory of the JVM
Table of Difference


In the vast landscape of Java programming, choosing between Anonymous Inner Classes and Lambda Expressions depends on the specific requirements of your code. While Anonymous Inner Classes offer flexibility and versatility, Lambda Expressions bring concise and expressive code to the forefront. Understanding the nuances between these constructs empowers developers to make informed decisions, ultimately enhancing the quality and readability of their code.

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