MathApp, Exercise.java

package com.example.mathapplication;

import java.util.Random;

public class Exercise {
    private static Random rnd = new Random();

    private int n1;
    private int n2;
    private String op;
    private double value;

    public Exercise() {
        n1 = Settings.min + rnd.nextInt(Settings.max - Settings.min + 1);
        n2 = Settings.min + rnd.nextInt(Settings.max - Settings.min + 1);
        int opIndex = rnd.nextInt(4);
        while (!isOpAllowd(opIndex)) {
            opIndex = rnd.nextInt(4);
        }

        switch (opIndex) {
            case 0:
                op = "+";
                value = n1 + n2;
                break;
            case 1:
                op = "-";
                value = n1 - n2;
                break;
            case 2:
                op = "*";
                value = n1 * n2;
                break;
            case 3:
                op = "/";
                value = n1 / n2;
                break;
        }

    }

    public int getN1() {
        return n1;
    }

    public int getN2() {
        return n2;
    }

    public String getOp() {
        return op;
    }

    public double getValue() {
        return value;
    }

    private boolean isOpAllowd(int op) {
        boolean allowed = false;

        switch (op) {
            case 0:
                allowed = Settings.add;
                break;
            case 1:
                allowed = Settings.sub;
                break;
            case 2:
                allowed = Settings.mul;
                break;
            case 3:
                allowed = Settings.div;
                break;
        }
        return allowed;
    }
}