From a9f5b8270839dde00e75c73eefbefd2d17b44b47 Mon Sep 17 00:00:00 2001
From: Alex Klymenko <alexanderklmn@gmail.com>
Date: Sun, 18 Aug 2024 20:58:57 +0200
Subject: [PATCH] refactor: `OctalToDecimal` (#5344)

---
 .../conversions/OctalToDecimal.java           | 57 +++++++++----------
 .../conversions/OctalToDecimalTest.java       | 21 ++++---
 2 files changed, 40 insertions(+), 38 deletions(-)

diff --git a/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java b/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java
index 187f0ed1..d91ce6eb 100644
--- a/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java
@@ -1,47 +1,42 @@
 package com.thealgorithms.conversions;
 
-import java.util.Scanner;
-
 /**
- * Converts any Octal Number to a Decimal Number
+ * Class for converting an octal number to a decimal number. Octal numbers are based on 8, using digits from 0 to 7.
  *
- * @author Zachary Jones
  */
 public final class OctalToDecimal {
+    private static final int OCTAL_BASE = 8;
+
     private OctalToDecimal() {
     }
 
     /**
-     * Main method
+     * Converts a given octal number (as a string) to its decimal representation.
+     * If the input is not a valid octal number (i.e., contains characters other than 0-7),
+     * the method throws an IllegalArgumentException.
      *
-     * @param args Command line arguments
-     */
-    public static void main(String[] args) {
-        Scanner sc = new Scanner(System.in);
-        System.out.print("Octal Input: ");
-        String inputOctal = sc.nextLine();
-        int result = convertOctalToDecimal(inputOctal);
-        if (result != -1) {
-            System.out.println("Result convertOctalToDecimal : " + result);
-        }
-        sc.close();
-    }
-
-    /**
-     * This method converts an octal number to a decimal number.
-     *
-     * @param inputOctal The octal number
-     * @return The decimal number
+     * @param inputOctal The octal number as a string
+     * @return The decimal equivalent of the octal number
+     * @throws IllegalArgumentException if the input is not a valid octal number
      */
     public static int convertOctalToDecimal(String inputOctal) {
-        try {
-            // Actual conversion of Octal to Decimal:
-            return Integer.parseInt(inputOctal, 8);
-        } catch (NumberFormatException ne) {
-            // Printing a warning message if the input is not a valid octal
-            // number:
-            System.out.println("Invalid Input, Expecting octal number 0-7");
-            return -1;
+        if (inputOctal == null || inputOctal.isEmpty()) {
+            throw new IllegalArgumentException("Input cannot be null or empty");
         }
+
+        int decimalValue = 0;
+
+        for (int i = 0; i < inputOctal.length(); i++) {
+            char currentChar = inputOctal.charAt(i);
+
+            if (currentChar < '0' || currentChar > '7') {
+                throw new IllegalArgumentException("Incorrect input: Expecting an octal number (digits 0-7)");
+            }
+
+            int currentDigit = currentChar - '0';
+            decimalValue = decimalValue * OCTAL_BASE + currentDigit;
+        }
+
+        return decimalValue;
     }
 }
diff --git a/src/test/java/com/thealgorithms/conversions/OctalToDecimalTest.java b/src/test/java/com/thealgorithms/conversions/OctalToDecimalTest.java
index 6e17ea14..20f0fa40 100644
--- a/src/test/java/com/thealgorithms/conversions/OctalToDecimalTest.java
+++ b/src/test/java/com/thealgorithms/conversions/OctalToDecimalTest.java
@@ -1,14 +1,21 @@
 package com.thealgorithms.conversions;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class OctalToDecimalTest {
 
-    @Test
-    public void testOctalToDecimal() {
-        assertEquals(1465, OctalToDecimal.convertOctalToDecimal("2671"));
-        assertEquals(189, OctalToDecimal.convertOctalToDecimal("275"));
+    @ParameterizedTest
+    @CsvSource({"10, 8", "7, 7", "77, 63", "123, 83", "0, 0", "777, 511", "2671, 1465", "275, 189"})
+    void testConvertOctalToDecimal(String inputOctal, int expectedDecimal) {
+        Assertions.assertEquals(expectedDecimal, OctalToDecimal.convertOctalToDecimal(inputOctal));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"'', Input cannot be null or empty", "'8', Incorrect input: Expecting an octal number (digits 0-7)", "'19', Incorrect input: Expecting an octal number (digits 0-7)"})
+    void testIncorrectInput(String inputOctal, String expectedMessage) {
+        IllegalArgumentException exception = Assertions.assertThrows(IllegalArgumentException.class, () -> OctalToDecimal.convertOctalToDecimal(inputOctal));
+        Assertions.assertEquals(expectedMessage, exception.getMessage());
     }
 }