Add Hexadecimal to binary conversion

src/main/java/com/conversions/HexadecimalToBinary.java

@@ -0,0 +1,48 @@
+package com.conversions;
+
+public class HexadecimalToBinary {
+	 /**
+     * This method converts a hexadecimal number to
+     * a binary number.
+     *
+     * @param hexStr The hexadecimal number
+     * @return The binary number
+     */
+	
+	public String hexToBin (String hexStr) {
+		
+		String binaryString = "", hexaNumbers = "0123456789ABCDEF";
+		int indexOfHex, decimalNumber = 0, k = 1;
+		char letter;
+		int binaryArray[] = new int [50];
+		
+		hexStr = hexStr.toUpperCase();
+		
+		/**
+		 * Transform the hexadecimal number to decimal number
+		 */
+		for ( int i = 0 ;  i < hexStr.length(); i++) {
+			letter = hexStr.charAt(i);
+			indexOfHex = hexaNumbers.indexOf(letter);
+			decimalNumber = 16 * decimalNumber + indexOfHex;
+		}
+
+		/**
+		 * Transform decimal number to binary and put it in an array
+		 */
+		while (decimalNumber != 0) {
+			binaryArray[k++] = decimalNumber % 2;
+			decimalNumber = decimalNumber / 2;
+		}
+		/**
+		 * Put the binary in a string
+		 */
+		for ( int j = k-1 ; j>0 ; j--) {
+			binaryString = binaryString + binaryArray[j];
+		}
+
+		return binaryString;
+		
+	}
+	
+}

src/test/java/com/conversions/HexadecimalToBinaryTest.java

@@ -0,0 +1,22 @@
+package com.conversions;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class HexadecimalToBinaryTest {
+
+	@Test
+	void test() {
+		HexadecimalToBinary hexadecimalToBinary = new HexadecimalToBinary();
+        Assertions.assertEquals("10101011", hexadecimalToBinary.hexToBin("AB"), "Incorrect Conversion");
+        Assertions.assertEquals("10101101010101111001101", hexadecimalToBinary.hexToBin("56ABCD"), "Incorrect Conversion");
+        Assertions.assertEquals("10011101111011010001001", hexadecimalToBinary.hexToBin("4ef689"), "Incorrect Conversion");
+        Assertions.assertEquals("10011101111", hexadecimalToBinary.hexToBin("4EF"), "Incorrect Conversion");
+        Assertions.assertEquals("101010111100110111101111", hexadecimalToBinary.hexToBin("ABCDEF"), "Incorrect Conversion");
+        //It returns -1 if you enter a wrong hexaDecimal
+        Assertions.assertEquals("-1", hexadecimalToBinary.hexToBin("K"), "Incorrect Conversion");
+	}
+
+}