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refactor: Enhance docs, remove main. add more tests in `HexaDecimal… #5923

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Original file line number Diff line number Diff line change
@@ -1,39 +1,45 @@
package com.thealgorithms.conversions;

import java.util.Scanner;

/**
* Utility class for converting a hexadecimal string to its decimal representation.
* <p>
* A hexadecimal number uses the base-16 numeral system, with the following characters:
* <ul>
* <li>Digits: 0-9</li>
* <li>Letters: A-F (case-insensitive)</li>
* </ul>
* Each character represents a power of 16. For example:
* <pre>
* Hexadecimal "A1" = 10*16^1 + 1*16^0 = 161 (decimal)
* </pre>
*
* <p>This class provides a method to perform the conversion without using built-in Java utilities.</p>
*/
public final class HexaDecimalToDecimal {
private HexaDecimalToDecimal() {
}

// convert hexadecimal to decimal
/**
* Converts a hexadecimal string to its decimal integer equivalent.
* <p>The input string is case-insensitive, and must contain valid hexadecimal characters [0-9, A-F].</p>
*
* @param hex the hexadecimal string to convert
* @return the decimal integer representation of the input hexadecimal string
* @throws IllegalArgumentException if the input string contains invalid characters
*/
public static int getHexaToDec(String hex) {
String digits = "0123456789ABCDEF";
hex = hex.toUpperCase();
int val = 0;

for (int i = 0; i < hex.length(); i++) {
int d = digits.indexOf(hex.charAt(i));
if (d == -1) {
throw new IllegalArgumentException("Invalid hexadecimal character: " + hex.charAt(i));
}
val = 16 * val + d;
}
return val;
}

// Main method gets the hexadecimal input from user and converts it into Decimal output.
public static void main(String[] args) {
String hexaInput;
int decOutput;
Scanner scan = new Scanner(System.in);

System.out.print("Enter Hexadecimal Number : ");
hexaInput = scan.nextLine();

// convert hexadecimal to decimal
decOutput = getHexaToDec(hexaInput);
/*
Pass the string to the getHexaToDec function
and it returns the decimal form in the variable decOutput.
*/
System.out.println("Number in Decimal: " + decOutput);
scan.close();
return val;
}
}
Original file line number Diff line number Diff line change
@@ -1,14 +1,37 @@
package com.thealgorithms.conversions;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvSource;

public class HexaDecimalToDecimalTest {

@Test
public void testhexaDecimalToDecimal() {
assertEquals(161, HexaDecimalToDecimal.getHexaToDec("A1"));
assertEquals(428, HexaDecimalToDecimal.getHexaToDec("1ac"));
@ParameterizedTest
@CsvSource({
"A1, 161", // Simple case with two characters
"1AC, 428", // Mixed-case input
"0, 0", // Single zero
"F, 15", // Single digit
"10, 16", // Power of 16
"FFFF, 65535", // Max 4-character hex
"7FFFFFFF, 2147483647" // Max positive int value
})
public void
testValidHexaToDecimal(String hexInput, int expectedDecimal) {
assertEquals(expectedDecimal, HexaDecimalToDecimal.getHexaToDec(hexInput));
}

@ParameterizedTest
@CsvSource({
"G", // Invalid character
"1Z", // Mixed invalid input
"123G", // Valid prefix with invalid character
"#$%" // Non-hexadecimal symbols
})
public void
testInvalidHexaToDecimal(String invalidHex) {
assertThrows(IllegalArgumentException.class, () -> HexaDecimalToDecimal.getHexaToDec(invalidHex));
}
}