refactor: Enhance docs, remove main. add more tests in HexaDecimalToBinary

Author: Hardvan

src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java

@@ -1,43 +1,60 @@
 package com.thealgorithms.conversions;
 
-// Hex [0-9],[A-F] -> Binary [0,1]
+/**
+ * Utility class for converting hexadecimal numbers to binary representation.
+ * <p>
+ * A hexadecimal number consists of digits from {@code [0-9]} and {@code [A-F]} (case-insensitive),
+ * while binary representation uses only {@code [0, 1]}.
+ * <p>
+ * This class provides methods to:
+ * <ul>
+ *   <li>Convert a hexadecimal string to its binary string equivalent.</li>
+ *   <li>Ensure the binary output is padded to 8 bits (1 byte).</li>
+ * </ul>
+ * <p>
+ * Example:
+ * <ul>
+ *   <li>{@code "A1"} → {@code "10100001"}</li>
+ *   <li>{@code "1"} → {@code "00000001"}</li>
+ * </ul>
+ *
+ * <p>This class assumes that the input hexadecimal string is valid.</p>
+ */
 public class HexaDecimalToBinary {
+
+    /**
+     * Converts a hexadecimal string to its binary string equivalent.
+     * The binary output is padded to a minimum of 8 bits (1 byte).
+     * Steps:
+     * <ol>
+     *     <li>Convert the hexadecimal string to an integer.</li>
+     *     <li>Convert the integer to a binary string.</li>
+     *     <li>Pad the binary string to ensure it is at least 8 bits long.</li>
+     *     <li>Return the padded binary string.</li>
+     * </ol>
+     *
+     * @param numHex the hexadecimal string (e.g., "A1", "7F")
+     * @throws NumberFormatException if the input string is not a valid hexadecimal number
+     * @return the binary string representation, padded to 8 bits (e.g., "10100001")
+     */
     public String convert(String numHex) {
-        // String a HexaDecimal:
         int conHex = Integer.parseInt(numHex, 16);
-        // Hex a Binary:
         String binary = Integer.toBinaryString(conHex);
-        // Output:
         return completeDigits(binary);
     }
 
+    /**
+     * Pads the binary string to ensure it is at least 8 bits long.
+     * If the binary string is shorter than 8 bits, it adds leading zeros.
+     *
+     * @param binNum the binary string to pad
+     * @return the padded binary string with a minimum length of 8
+     */
     public String completeDigits(String binNum) {
-        final int longBits = 8;
-        for (int i = binNum.length(); i < longBits; i++) {
+        final int BYTE_SIZE = 8;
+        while (binNum.length() < BYTE_SIZE) {
             binNum = "0" + binNum;
         }
         return binNum;
     }
-
-    public static void main(String[] args) {
-        // Testing Numbers:
-        String[] hexNums = {
-            "1",
-            "A1",
-            "ef",
-            "BA",
-            "AA",
-            "BB",
-            "19",
-            "01",
-            "02",
-            "03",
-            "04",
-        };
-        HexaDecimalToBinary objConvert = new HexaDecimalToBinary();
-
-        for (String num : hexNums) {
-            System.out.println(num + " = " + objConvert.convert(num));
-        }
-    }
 }

src/test/java/com/thealgorithms/conversions/HexaDecimalToBinaryTest.java

@@ -2,14 +2,32 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class HexaDecimalToBinaryTest {
 
-    @Test
-    public void testHexaDecimalToBinary() {
-        HexaDecimalToBinary hexaDecimalToBinary = new HexaDecimalToBinary();
-        assertEquals("1111111111111111111111111111111", hexaDecimalToBinary.convert("7fffffff"));
-        assertEquals("101010111100110111101111", hexaDecimalToBinary.convert("abcdef"));
+    private final HexaDecimalToBinary converter = new HexaDecimalToBinary();
+
+    @ParameterizedTest
+    @CsvSource({"1, 00000001", "A1, 10100001", "EF, 11101111", "BA, 10111010", "7, 00000111", "F, 00001111", "7FFFFFFF, 1111111111111111111111111111111", "ABCDEF, 101010111100110111101111"})
+    public void testHexaDecimalToBinary(String hexInput, String expectedBinary) {
+        assertEquals(expectedBinary, converter.convert(hexInput));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"0, 00000000", "2, 00000010", "3, 00000011"})
+    public void testPaddingWithLeadingZeros(String hexInput, String expectedBinary) {
+        assertEquals(expectedBinary, converter.convert(hexInput));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"G, NumberFormatException", "ZZ, NumberFormatException"})
+    public void testInvalidHexInput(String hexInput, String expectedException) {
+        try {
+            converter.convert(hexInput);
+        } catch (NumberFormatException e) {
+            assertEquals(expectedException, e.getClass().getSimpleName());
+        }
     }
 }