Lecture on Lambda Expressions

Overview

• Lambda Expressions: A feature to simplify the code of anonymous inner classes, introduced in Java.

Functional Interface

• Concept: Interfaces with only one abstract method.
• Example: Interface A with method show(). interface A { void show(); }

Traditional Anonymous Inner Class

• Instantiation: Normally, you instantiate a class implementing an interface with an anonymous inner class. A obj = new A() { public void show() { // method implementation } };

Using Lambda Expressions

• Simplification: Reduce the verbosity of anonymous inner classes.
• Syntax: Replaces the need to declare the method and the unnecessary overhead. A obj = () -> { // method implementation };
  • Arrow Token (->): Key part of Lambda syntax.

Reduction and Syntactic Sugar

• Without Curly Braces: If the method contains only one statement. A obj = () -> System.out.println("Show method");
• Benefits: Cleaner and shorter code.

Lambda Expressions with Parameters

• Method with Parameters: If show accepts an integer parameter. interface A { void show(int i); }
  • Anonymous Inner Class: A obj = new A() { public void show(int i) { System.out.println("Value: " + i); } };
  • Lambda Expression: Simplified version accepting a parameter. A obj = (int i) -> System.out.println("Value: " + i);

Removing Variable Type and Parentheses

• Type Inference: Java infers the type from the interface declaration. A obj = (i) -> System.out.println("Value: " + i);
• Single Parameter Simplification: Parentheses can be omitted when there's only one parameter. A obj = i -> System.out.println("Value: " + i);

Compilation and Class Files

• Class File Management: Lambda expressions reduce the number of generated class files but may increase the size of the .java file.

Next Steps

• Return Types and Multiple Parameters: To be covered in the next video.