Multiply two hexadecimal values

I've written an algorithm which can multiply two hex values and return a hex as a result. What do you think about the below solution?

```
package com.datastructute.arraystring;

public class hexadecimal {
public static void main(String[] args) {

System.out.println(multiplyHex("AE08FE2111111111", "BF"));
System.out.println(multiplyHex("DF", "BC")); // A3C4
System.out.println(multiplyHex("ADF398", "BA48")); // 7e93e8f2c0

// Test Screnarios
System.out.println(multiplyHex(null, null));
System.out.println(multiplyHex(" ", " "));
System.out.println(multiplyHex("hyh", "hyhy"));
System.out.println(multiplyHex("abyh", "ashyhy"));
System.out.println(multiplyHex("-1-1-1", "-1-1-1"));
System.out.println(multiplyHex("AE08FE2111111111AE08FE2AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE2111111111AE08FE21111111111111AE08FE2111111111AE08FE21111111111111AE08FE21111AE08FE211111111111111", "AE0AE08FE21111111118FE2111111111AE08FE2111111111"));
}

public static String multiplyHex(String str1, String str2) {
if(str1 == null || str2 == null)
return "Null values are not accepted.";

char[] hex1 = str1.toCharArray();
char[] hex2 = str2.toCharArray();

int[][] ArrHexMatrix;
int arrLength = hex1.length + hex2.length;
int arrIndexLength = hex1.length + hex2.length - 1;
int lines = hex2.length;
ArrHexMatrix = new int[hex2.length][arrLength];

int mod = 0;
int carry = 0;
int count = 0;
int index = 0;

for (int i = lines - 1; i >= 0; i--) {

carry = 0;
count = 0;
for (int j = hex1.length - 1; j >= 0; j--) {
try {

Your getInt and getChar methods are very long and cumbersome, they can be replaced by this:

Using arrays:

private char[] values = new char[]{ '0', '1', '2', '3', '4', '5', '6', '7',
      '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

char getInt(int i) {
    return values[i];
}

Java has already built-in methods to do this conversion though, so all that is needed is really:

int getInt(char chr) {
    return Character.digit(chr, 16);
}

char getChar(int val) {
    return Character.forDigit(val, 16);
}

Hexadecimal values are often showed in lower-case, personally I like that better because it makes it easier to separate the characters (a-f) from the digits (0-9). If you still want to use upper-case characters though, use this:

return Character.toUpperCase(Character.forDigit(val, 16));

private static char getChar(int val) throws Exception {

Don't throw Exception, use IllegalArgumentException instead. IllegalArgumentException is a RuntimeException and therefore does not need to be caught (or declared in the throws declaration), but you are still free to do so if you would like. (Although I would not recommend it)

Learn to use JUnit to do the testing.

import static org.junit.Assert.*;

public class MultiplyHexTest {
    @Test
    public void testSomething() {
        assertEquals("A3C4", multiplyHex("DF", "BC"));
    }

    @Test(expected = IllegalArgumentException.class)
    public void testFailure() {
        multiplyHex("  ", "  ");
    }
}

ArrHexMatrix, being a name for a variable, should start with a lowercase character according to the Java naming conventions.

StackExchange Code Review Q#52084, answer score: 12