Add 'Simple Math' solution

Author: durimkryeziu

README.md

@@ -8,7 +8,7 @@ Exercises for Programmers: 57 Challenges to Develop Your Coding Skills by Brian
 - Exercise 2. [Counting the Number of Characters](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/characters-count)
 - Exercise 3. [Printing Quotes](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/printing-quotes)
 - Exercise 4. [Mad Lib](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/mad-lib)
-- Exercise 5. Simple Math
+- Exercise 5. [Simple Math](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/simple-math)
 - Exercise 6. Retirement Calculator
 
 **Calculations**

settings.gradle

@@ -1,2 +1,2 @@
 rootProject.name = 'exercises-for-programmers-java'
-include('saying-hello', 'characters-count', 'printing-quotes', 'mad-lib')
+include('saying-hello', 'characters-count', 'printing-quotes', 'mad-lib', 'simple-math')

simple-math/build.gradle

@@ -0,0 +1,8 @@
+plugins {
+    id 'com.craftsmanshipinsoftware.common-conventions'
+}
+
+dependencies {
+    testImplementation(libs.assertj.core)
+    testImplementation(libs.junit.jupiter)
+}

simple-math/src/main/java/com/craftsmanshipinsoftware/math/Main.java

@@ -0,0 +1,9 @@
+package com.craftsmanshipinsoftware.math;
+
+public class Main {
+
+  public static void main(String[] args) {
+    SimpleMath simpleMath = new SimpleMath(System.in, System.out);
+    simpleMath.printOutput();
+  }
+}

simple-math/src/main/java/com/craftsmanshipinsoftware/math/SimpleMath.java

@@ -0,0 +1,86 @@
+package com.craftsmanshipinsoftware.math;
+
+import java.io.InputStream;
+import java.io.PrintStream;
+import java.util.Objects;
+import java.util.Scanner;
+
+class SimpleMath {
+
+  private final PrintStream printStream;
+  private final InputStream inputStream;
+
+  SimpleMath(InputStream inputStream, PrintStream printStream) {
+    Objects.requireNonNull(inputStream, "inputStream must not be null");
+    Objects.requireNonNull(printStream, "printStream must not be null");
+    this.printStream = printStream;
+    this.inputStream = inputStream;
+  }
+
+  void printOutput() {
+    try (Scanner scanner = new Scanner(inputStream)) {
+      String firstInput = promptForInput("What is the first number? ", scanner);
+      int firstNumber = validatedInput(firstInput);
+      String secondInput = promptForInput("What is the second number? ", scanner);
+      int secondNumber = validatedInput(secondInput);
+      if (secondNumber == 0) {
+        throw new IllegalArgumentException("Cannot divide by zero!");
+      }
+      this.printStream.println(output(firstNumber, secondNumber));
+    }
+  }
+
+  @SuppressWarnings("PMD.SystemPrintln")
+  private String promptForInput(String prompt, Scanner scanner) {
+    System.out.print(prompt);
+    String input = readInput(scanner);
+    if (input == null || input.isBlank()) {
+      throw new IllegalArgumentException("Input must not be empty!");
+    }
+    return input;
+  }
+
+  private String readInput(Scanner scanner) {
+    return scanner.hasNext() ? scanner.nextLine() : null;
+  }
+
+  private static int validatedInput(String input) {
+    try {
+      int number = Integer.parseInt(input);
+      if (number < 0) {
+        throw new IllegalArgumentException("Please enter a positive number! Input: " + number);
+      }
+      return number;
+    } catch (NumberFormatException e) {
+      throw new IllegalArgumentException("Please enter a valid number! Input: " + input, e);
+    }
+  }
+
+  private static String output(int firstNumber, int secondNumber) {
+    return String.format("""
+            %d + %d = %d
+            %d - %d = %d
+            %d * %d = %d
+            %d / %d = %d""",
+        firstNumber, secondNumber, add(firstNumber, secondNumber),
+        firstNumber, secondNumber, subtract(firstNumber, secondNumber),
+        firstNumber, secondNumber, multiply(firstNumber, secondNumber),
+        firstNumber, secondNumber, divide(firstNumber, secondNumber));
+  }
+
+  private static int add(int firstNumber, int secondNumber) {
+    return firstNumber + secondNumber;
+  }
+
+  private static int subtract(int firstNumber, int secondNumber) {
+    return firstNumber - secondNumber;
+  }
+
+  private static int multiply(int firstNumber, int secondNumber) {
+    return firstNumber * secondNumber;
+  }
+
+  private static int divide(int firstNumber, int secondNumber) {
+    return firstNumber / secondNumber;
+  }
+}

simple-math/src/test/java/com/craftsmanshipinsoftware/math/SimpleMathTest.java

@@ -0,0 +1,84 @@
+package com.craftsmanshipinsoftware.math;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+class SimpleMathTest {
+
+  @ParameterizedTest
+  @ValueSource(strings = {"", " ", "10\n", "\n5"})
+  void inputIsRequired(String input) {
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream(input.getBytes()), new PrintStream(new ByteArrayOutputStream()));
+
+    assertThatIllegalArgumentException()
+        .isThrownBy(simpleMath::printOutput)
+        .withMessage("Input must not be empty!");
+  }
+
+  @Test
+  void firstInputMustBeANumber() {
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream("abc".getBytes()), new PrintStream(new ByteArrayOutputStream()));
+
+    assertThatIllegalArgumentException()
+        .isThrownBy(simpleMath::printOutput)
+        .withMessage("Please enter a valid number! Input: abc");
+  }
+
+  @Test
+  void firstNumberMustBePositive() {
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream("-10\n5".getBytes()), new PrintStream(new ByteArrayOutputStream()));
+
+    assertThatIllegalArgumentException()
+        .isThrownBy(simpleMath::printOutput)
+        .withMessage("Please enter a positive number! Input: -10");
+  }
+
+  @Test
+  void secondInputMustBeANumber() {
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream("10\nasdf".getBytes()), new PrintStream(new ByteArrayOutputStream()));
+
+    assertThatIllegalArgumentException()
+        .isThrownBy(simpleMath::printOutput)
+        .withMessage("Please enter a valid number! Input: asdf");
+  }
+
+  @Test
+  void secondNumberMustBePositive() {
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream("10\n-5".getBytes()), new PrintStream(new ByteArrayOutputStream()));
+
+    assertThatIllegalArgumentException()
+        .isThrownBy(simpleMath::printOutput)
+        .withMessage("Please enter a positive number! Input: -5");
+  }
+
+  @Test
+  void secondNumberMustNotBeZero() {
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream("10\n0".getBytes()), new PrintStream(new ByteArrayOutputStream()));
+
+    assertThatIllegalArgumentException()
+        .isThrownBy(simpleMath::printOutput)
+        .withMessage("Cannot divide by zero!");
+  }
+
+  @Test
+  void sumDifferenceProductAndQuotientIsPrinted() {
+    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+    SimpleMath simpleMath = new SimpleMath(new ByteArrayInputStream("10\n5".getBytes()), new PrintStream(outputStream));
+
+    simpleMath.printOutput();
+
+    assertThat(outputStream).hasToString("""
+        10 + 5 = 15
+        10 - 5 = 5
+        10 * 5 = 50
+        10 / 5 = 2
+        """);
+  }
+}