Understanding Low-Level Design Principles in Java—Part 1
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Chapter 1: Key Principles of Low-Level Design
Low-level design (LLD) is crucial for crafting robust software systems. This chapter delves into essential concepts, illustrated with practical Java examples.
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Section 1.1: Modularity
Definition: Modularity is the design principle of separating a system into distinct modules that can function independently yet interact smoothly.
Example: Imagine a simple Java application for processing orders and payments. We can divide this application into two modules: OrderProcessor and PaymentProcessor.
// Module 1: Order Processing
public class OrderProcessor {
public void processOrder(String orderId) {
System.out.println("Processing order: " + orderId);
// Logic for processing orders
}
}
// Module 2: Payment Processing
public class PaymentProcessor {
public void processPayment(String orderId, double amount) {
System.out.println("Processing payment for order: " + orderId + " of amount $" + amount);
// Logic for processing payments
}
}
// Main class to utilize the modules
public class Main {
public static void main(String[] args) {
OrderProcessor orderProcessor = new OrderProcessor();
PaymentProcessor paymentProcessor = new PaymentProcessor();
String orderId = "ORD123";
double amount = 100.0;
orderProcessor.processOrder(orderId);
paymentProcessor.processPayment(orderId, amount);
}
}
Section 1.2: Functional Decomposition
Definition: Functional decomposition is the method of breaking down a complex task into smaller, manageable functions that are easier to comprehend.
Example: Let's simplify the process of sending an email into smaller functions within an EmailSender class.
public class EmailSender {
public void sendEmail(String to, String subject, String body) {
connectToServer();
authenticate();
createEmail(to, subject, body);
send();
disconnect();
}
private void connectToServer() {
System.out.println("Connecting to email server...");}
private void authenticate() {
System.out.println("Authenticating...");}
private void createEmail(String to, String subject, String body) {
System.out.println("Creating email to: " + to + " with subject: " + subject);}
private void send() {
System.out.println("Sending email...");}
private void disconnect() {
System.out.println("Disconnecting from server...");}
}
Section 1.3: Data Structures
Definition: Data structures are methods for organizing and storing data efficiently, allowing for easy access and modification.
Example: Here's how to implement a basic stack using an array in Java.
public class Stack {
private int[] elements;
private int size;
private int capacity;
public Stack(int capacity) {
this.capacity = capacity;
elements = new int[capacity];
size = 0;
}
public void push(int element) {
if (size == capacity) {
throw new IllegalStateException("Stack is full");}
elements[size++] = element;
}
public int pop() {
if (size == 0) {
throw new IllegalStateException("Stack is empty");}
return elements[--size];
}
public int peek() {
if (size == 0) {
throw new IllegalStateException("Stack is empty");}
return elements[size - 1];
}
}
Section 1.4: Interfaces
Definition: Interfaces in Java outline a contract defining the actions a class must perform, without dictating how these actions are carried out.
Example: Below is the definition and implementation of a Drivable interface for vehicles.
public interface Drivable {
void drive();
}
public class Car implements Drivable {
public void drive() {
System.out.println("Car is driving.");}
}
public class Bicycle implements Drivable {
public void drive() {
System.out.println("Bicycle is being pedaled.");}
}
Section 1.5: API Design
Definition: API design involves specifying methods that allow other developers to utilize your software's capabilities.
Example: Here’s a straightforward API for a calculator.
public class Calculator {
// API to add two numbers
public int add(int a, int b) {
return a + b;}
// API to subtract two numbers
public int subtract(int a, int b) {
return a - b;}
// API to multiply two numbers
public int multiply(int a, int b) {
return a * b;}
// API to divide two numbers
public double divide(double a, double b) {
if (b == 0) {
throw new IllegalArgumentException("Divider cannot be zero.");}
return a / b;
}
}
Each of these examples demonstrates fundamental low-level design concepts through straightforward Java code, making it suitable for beginners eager to learn software design principles.
Chapter 2: Additional Resources
To deepen your understanding of low-level design, consider these informative videos:
This video, titled "LLD RoadMap | What to study for Low Level System Design Interviews," provides a comprehensive guide on what topics to focus on for low-level design interviews.
In this video, "Design a Vending Machine | LLD Interview Question | State Design Patterns | OOPS | Java," you will learn about applying state design patterns to solve practical interview questions.