Java Programming - Lecture 39

Java Programming

Lecture 39: Lambda Expressions and Functional Interfaces

GTU Diploma in Computer Engineering

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Learning Objectives

After this lecture, you will be able to:

  • Understand functional programming concepts in Java
  • Write and use lambda expressions effectively
  • Work with built-in functional interfaces
  • Create custom functional interfaces
  • Use method references and constructor references
  • Apply functional programming patterns
  • Understand the benefits of functional style programming

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Lecture Overview

  1. Introduction to Functional Programming
  2. Lambda Expression Syntax
  3. Functional Interfaces
  4. Built-in Functional Interfaces
  5. Method References
  6. Custom Functional Interfaces
  7. Functional Programming Patterns
  8. Best Practices
  9. Hands-on Exercises

What is Functional Programming?

Functional programming is a programming paradigm that treats computation as evaluation of mathematical functions.

Key Concepts

  1. Functions as First-Class Objects: Functions can be assigned to variables, passed as parameters
  2. Immutability: Data doesn't change after creation
  3. Pure Functions: Functions with no side effects
  4. Higher-Order Functions: Functions that take or return other functions

Java 8 and Functional Programming

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Introduction to Lambda Expressions

Lambda expressions provide a concise way to represent anonymous functions.

Syntax

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Comparison with Anonymous Classes

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Lambda Expression Examples

Basic Examples

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Functional Interfaces

A functional interface has exactly one abstract method (SAM - Single Abstract Method).

@FunctionalInterface Annotation

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Using Functional Interfaces

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Built-in Functional Interfaces

Java 8 provides many built-in functional interfaces in java.util.function package.

Predicate<T>

Tests a condition and returns boolean.

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Function<T, R>

Represents a function that takes one argument and returns a result.

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Consumer<T> and Supplier<T>

Consumer<T> - Consumes input, returns nothing

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Supplier<T> - Supplies a value

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Method References

Method references provide a way to refer to methods without executing them.

Types of Method References

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Constructor References

Constructor references are a special form of method references.

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Custom Functional Interfaces

Creating your own functional interfaces for specific use cases.

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Using Custom Functional Interfaces

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Functional Programming Patterns

Higher-Order Functions

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Currying and Partial Application

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Functional Composition

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Best Practices

1. Keep Lambdas Simple and Readable

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2. Prefer Method References When Appropriate

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3. Use Appropriate Functional Interfaces

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Performance Considerations

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Hands-on Exercise 1: Event Processing System

Create a functional event processing system with the following requirements:

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Test your implementation with different event types and processors.

Hands-on Exercise 2: Functional Calculator

Implement a calculator using functional programming concepts:

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Include error handling and support for custom operations.

Hands-on Exercise 3: Data Processing Pipeline

Create a functional data processing pipeline:

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Test with various data transformations and operations.

Exercise Solutions: Event Processing System

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Summary

Key Concepts Covered

  1. Functional Programming: Treating functions as first-class objects
  2. Lambda Expressions: Concise syntax for anonymous functions
  3. Functional Interfaces: Interfaces with single abstract method
  4. Built-in Interfaces: Predicate, Function, Consumer, Supplier
  5. Method References: Referencing methods without executing them
  6. Constructor References: Referencing constructors as functions
  7. Function Composition: Combining functions to create complex operations

Benefits of Functional Programming

  • Conciseness: Less boilerplate code
  • Readability: More expressive code
  • Reusability: Functions can be composed and reused
  • Testability: Pure functions are easier to test
  • Parallelization: Functional code is often easier to parallelize

When to Use Functional Programming

  • Data processing and transformations
  • Event handling and filtering
  • Collections operations
  • Configuration and setup code
  • Validation and business rules

Next Lecture Preview

Lecture 40: Stream API

  • Introduction to Java Streams
  • Creating and Operating on Streams
  • Intermediate and Terminal Operations
  • Parallel Streams
  • Collectors and Custom Collectors
  • Stream Performance and Best Practices

Preparation

  • Practice with lambda expressions and functional interfaces
  • Review collections framework
  • Understand the concept of lazy evaluation

Thank You!

Questions and Discussion

  • How do lambda expressions improve code readability?
  • When would you choose lambda expressions over anonymous classes?
  • What are the performance implications of functional programming?

Resources for Further Learning

  • Oracle Java Lambda Tutorial
  • Functional Programming in Java by Venkat Subramaniam
  • Practice functional programming with different use cases

Next: Stream API and Functional Data Processing