Stop writing code inside main method
Stop writing code inside main method
November 29, 2020
Introduction
Greetings to everyone who reads this post! Due to my work, I often run into novice programmers and look at their code. Sometimes it is beautiful, sometimes not, but I understand that a person learns, and the further he masters the best practices and technologies, the better his code becomes. But I would still like to pay some attention to such a simple task that almost all novice programmers face — writing a calculator.
Here’s what novice programmers write:
Calculator.java
import java.util.Scanner;
public class Calculator {
public static void main(String[] args) {
int sum = 0;
int number1 = 0, number2 = 0;
boolean correct = true;
char operation1;
Scanner sc = new Scanner(System.in);
System.out.println("Enter first number:");
while (!sc.hasNextInt()) {
System.out.println("Sorry, it is not a digit. Try again, please");
sc.next();
}
number1 = sc.nextInt();
System.out.println("Thanks! You entered number: " + number1);
System.out.println("Enter a number:");
while (!sc.hasNextInt()) {
System.out.println("It is not a digit. Try again");
sc.next();
}
number2 = sc.nextInt();
System.out.println("Thanks! It is a digit " + number2);
do {
correct = true;
System.out.println("What would you like to do? + - / *");
operation1 = sc.next().charAt(0);
switch (operation1) {
case '+':
sum = number1 + number2;
System.out.println("Sum of this two equals to " + sum);
break;
case '-':
sum = number1 - number2;
System.out.println("The difference between equals to: " + sum);
break;
case '/':
if (number2 != 0) {
sum = number1 / number2;
System.out.println("Divied equals to: " + sum);
} else {
System.out.println("Divided by zero is not allowed.");
correct = false;
}
break;
case '*':
sum = number1 * number2;
System.out.println("Multiplication of this two: " + sum);
break;
default:
System.out.println("Unknow operation");
correct = false;
break;
}
} while (correct != true);
}
}What problems do you see in this code? I see the following problems
- Everything is written in the main method, and certainly represents more than 10 lines
- There are no tests for this code, that is, there is no confidence that it will work correctly
- Structural programming style — the switch statement encourages this
- Using the Scanner, but it can be forgiven because it has convenient methods for getting numbers right away.