The challenge
Convert an integer which is base 10, to a hexadecimal base 16 string.
Java provides various built-in options such as Integer.toString(a, 16), or String.format("0x%X", a), or Integer.toHexString(a)
The solution in Java code
Option 1:
public class Hexadecimal{
public static String convertToHex(int a){
return "0x"+Integer.toHexString(a).toUpperCase();
}
}
Option 2:
public class Hexadecimal{
private static final String hexDigits = "0123456789ABCDEF";
public static String convertToHex(int a) {
String hexadecimal = "";
while (a > 0) {
int digit = a % 16;
hexadecimal = hexDigits.charAt(digit) + hexadecimal;
a = a / 16;
}
return "0x" + hexadecimal;
}
}
Option 3:
public class Hexadecimal{
private static final String HEX = "0123456789ABCDEF";
public static String convertToHex(int a){
final StringBuilder sb = new StringBuilder("");
while (a != 0) {
sb.append(HEX.charAt((a & 0xf)));
a = a >> 4;
}
return "0x" + sb.reverse().toString();
}
}
Option 4:
public class Hexadecimal {
private static final char[] numbers = {'0' , '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
public static String convertToHex(int a) {
if (a < 16)
return "0x" + numbers[a];
return convertToHex(a/16) + numbers[a%16];
}
}
Test cases to validate our solution
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class HexadecimalShould {
@Test
public void test (){
assertEquals("0x100",Hexadecimal.convertToHex(256));
}
}
Additional test cases
import org.junit.Test;
import java.util.HashMap;
import static org.junit.Assert.assertEquals;
public class HexadecimalShould {
@Test
public void test (){
assertEquals("0x100",Hexadecimal.convertToHex(256));
int numbers[] = new int[1000];
for (int i = 0; i < numbers.length; i++) {
numbers[i] = (int)Math.floor(Math.random()*4294967295.);
assertEquals((new Hex()).convertToHex(numbers[i]),Hexadecimal.convertToHex(numbers[i]));
}
}
private class Hex {
public String convertToHex(int a) {
String num = "";
HashMap<String, String> mapeo = new HashMap<>();
for (int i = 0; i < 10; i++) mapeo.put(i + "", i + "");
mapeo.put("10", "A");
mapeo.put("11", "B");
mapeo.put("12", "C");
mapeo.put("13", "D");
mapeo.put("14", "E");
mapeo.put("15", "F");
while (a >= 16) {
num += mapeo.get(a % 16 + "") + "";
a /= 16;
}
num += mapeo.get(a + "");
return "0x"+(new StringBuilder(num)).reverse().toString();
}
}
}