Maths test program

Naming and Problem Decomposition

• Class names should be nouns; method names should be verbs. If you have a method named as a noun like sumGenerator(), that’s a red flag.
• Each method should do one thing only; its name should reflect its purpose. If you have a method named answerGetter_score(), that’s a red flag. Is it getting an answer and keeping score? It also breaks the standard interCapsNaming() convention.
• Each class should do one thing only; its name should reflect its purpose. I have no idea what a Machine or a calcu is. The latter also breaks the standard capitalization convention.
• Separate your input/output routines from the calculation routines. Forcing yourself to separate the two helps you come up with clean designs.
• Keep your main() function minimal. The temptation to stuff a lot of functionality into main() leads to sloppy design.
• Avoid hard-coding assumptions in more than one place. What if you want to change the length of the quiz? Currently, 5 is hard-coded in several places. It’s easy to introduce a bug if someone fails to make the same change everywhere.

For this problem, I think that there should be two classes: SumGenerator and ArithmeticQuiz. SumGenerator is responsible for making random addition questions. ArithmeticQuiz “drives” it.

What if you want to change the quiz to do multiplication? Just swap out the SumGenerator for a ProductGenerator. To ease that transition, it would be helpful to define a QuestionGenerator interface.

Code Formatting (only because you asked about good habits)

Consistent indentation is very important for readability. Do that, and discard the noisy //end comments.

Also, add some horizontal spacing around punctuation, such as comparison operators.

The one-point penalty for an incorrect answer deserves a comment, since not everyone expects that behaviour.

Proposed Solution

QuestionGenerator.java:

interface QuestionGenerator {
    void next();
    String getQuestion();
    int getAnswer();
}

SumGenerator.java:

import java.util.Random;

class SumGenerator implements QuestionGenerator {
    private int maxAddend, num1, num2, ans;
    private Random rand = new Random();

    public SumGenerator(int maxAddend) {
        this.maxAddend = maxAddend;
        this.next();
    }

    @Override
    public void next() {
        num1 = rand.nextInt(this.maxAddend + 1);
        num2 = rand.nextInt(this.maxAddend + 1);
        ans = num1 + num2;
    }

    @Override
    public String getQuestion() {
        return num1 + " + " + num2;
    }

    @Override
    public int getAnswer() {
        return ans;
    }
}

ArithmeticQuiz.java:

import java.util.Scanner;

public class ArithmeticQuiz {
    private int length;
    private QuestionGenerator questions;

    public ArithmeticQuiz(int length, QuestionGenerator q) {
        this.length = length;
        this.questions = new SumGenerator();
    }

    public void run() {
        // Closing the Scanner after use is a good habit.
        // Automatically closing the Scanner using the
        // try-with-resources feature of Java 7 is even better.
        try (Scanner in = new Scanner(System.in)) {
            int score = 0; 
            for (int i = this.length; i > 0; i--) {
                System.out.println(this.questions.getQuestion());
                int answer = in.nextInt();
                if (this.questions.getAnswer() == answer) {
                    score++;
                    System.out.println("Correct");
                }else{
                    score--;    // Penalty for incorrect answer
                    System.out.println("Incorrect");
                }
                System.out.printf("Score is currently: %d/%d\n", score, this.length);
                this.questions.next();
            }
        }
    }

    public static void main(String[] args) {
        System.out.println("***Welcome to addition Math test***");
        ArithmeticQuiz quiz = new ArithmeticQuiz(5, new SumGenerator(9));
        quiz.run();
        System.out.println("Thanks for taking the test.");
    }
}