SOLID I - Finding and fixing SRP violations

[kanmaytacker]

What?
Find SRP violations in this package and refactor it to adhere to SRP.

Why?
Better understanding of SRP.
SRP helps with maintainability and extensibility of an application.

How?

• Consider moving methods to separate classes
• Abstract classes vs interface
• Add a submission link in the discussion below.

[PrakashGatiyala]

There is problem with printInvoice method. It is printing four different types of stuff namely book details, discount rate, tax rate and total.
All these 4 details should have separate method for printing details. printInvoice method is monster/God method.

 public void printInvoice() {
//        System.out.println(quantity + "x " + book.getName() + " " + book.getPrice() + "$");
//        System.out.println("Discount Rate: " + discountRate);
//        System.out.println("Tax Rate: " + taxRate);
//        System.out.println("Total: " + total);
        printBookDetails();
        printDiscountRate();
        printTaxRate();
        printTotal();
    }

---

Complete Code

package com.scaler.lld.questions;

import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import lombok.Getter;

@Getter
@AllArgsConstructor
public class Invoice {
    private Book book;
    private Integer quantity;
    private Double discountRate;
    private Double taxRate;

    @Getter(AccessLevel.NONE)
    private double total; // Will not generate a getter

    public Double getTotal() {
        double price = ((book.getPrice() - book.getPrice() * discountRate) * this.quantity);
        return price * (1 + taxRate);
    }

    public void printInvoice() {
//        System.out.println(quantity + "x " + book.getName() + " " + book.getPrice() + "$");
//        System.out.println("Discount Rate: " + discountRate);
//        System.out.println("Tax Rate: " + taxRate);
//        System.out.println("Total: " + total);
        printBookDetails();
        printDiscountRate();
        printTaxRate();
        printTotal();
    }
    public void printBookDetails(){
        System.out.println(quantity + "x " + book.getName() + " " + book.getPrice() + "$");
    }
    public void printDiscountRate(){
        System.out.println("Discount Rate: " + discountRate);
    }
    public void printTaxRate(){
        System.out.println("Tax Rate: " + taxRate);
    }
    public void printTotal(){
        System.out.println("Total: " + total);
    }

    public void saveToFile(String filename) {
        // Creates a file with given name and writes the invoice
    }

}