Can you find help me understand why this is failing the toHex(int) requirement?

Question about the task

Hexadecimal converter

Java Syntax, Level 9, Lesson 2

Under discussion

The public static toHex(String) method must convert the integer received as an input parameter from the decimal numeral system to hexadecimal and return its string representation.
And conversely, the public static toDecimal(String) method converts from the string representation of a hexadecimal number to the string representation of a decimal number.

The methods only work with positive numbers and non-empty strings.
If the input parameter is less than or equal to 0, the toHex(int) method returns an empty string.
If the input parameter is an empty string or null, then the toDecimal(String) method returns 0.
Your task is to implement these methods.

Also the Solution class has a HEX constant, which contains all the characters used in the hexadecimal system.

One algorithm for converting a decimal number to hexadecimal is as follows:


while (the decimal number is not 0) {
the hexadecimal representation = the character in the HEX string that has an index equal to the remainder of the decimal number divided by 16
+ the hexadecimal representation of the number
the decimal number = the decimal number / 16
}

One algorithm for converting a hexadecimal number to decimal is as follows:


for (int i = 0; i < length of the input string; i++) {
the decimal number = 16 * the decimal number + the index of the character in the HEX string that is equal to the character in the input string at index i
}

The main() method is not involved in testing.

Requirements:

The toHex(int) method needs to be implemented as outlined in the task conditions.
The toDecimal(String) method needs to be implemented as outlined in the task conditions.
The Integer.toHexString(int) and Long.toHexString(int) methods cannot be used.
The Integer.parseInt(String, int) and Long.parseLong(String, int) methods cannot be used.
The Integer.toString(int, int) and Long.toString(long, int) methods cannot be used.
You cannot use a BigInteger object.
You cannot use a BigDecimal object.

package en.codegym.task.pro.task09.task0907; /* Hexadecimal converter */ public class Solution { private static final String HEX = "0123456789abcdef"; public static void main(String[] args) { int decimalNumber =-1; System.out.println("Decimal number " + decimalNumber + " is equal to hexadecimal number " + toHex(decimalNumber)); String hexNumber = "4e8"; System.out.println("Hexadecimal number " + hexNumber + " is equal to decimal number " + toDecimal(hexNumber)); } public static String toHex(int decimalNumber) { if (decimalNumber <=0) return ""; int i=0; String hex=""; while ((int)(decimalNumber/Math.pow(16,i))>0)i++; int j=i-1; while (decimalNumber>0){ int a = (int)((decimalNumber/Math.pow(16,j))); int b= (int)(a*Math.pow(16,j)); String c = HEX.substring(a,a+1); hex = hex+c; decimalNumber=decimalNumber-b; j--; } return hex; } public static int toDecimal(String hexNumber) { if (hexNumber==null)return 0; if (hexNumber.length()<1) return 0; int decimal = 0; int StringLength = hexNumber.length(); for(int i=0; i<hexNumber.length(); i++){ decimal = decimal + HEX.indexOf(hexNumber.substring(i,i+1)) * (int) Math.pow(16,(hexNumber.length()-1-i)); } return decimal; } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

8 April 2022, 14:24

useful

Do you need an example where the above code outputs the incorrect result? Try:

int decimalNumber = 1048576;
System.out.println("Decimal number " + decimalNumber + " is equal to hexadecimal number " + toHex(decimalNumber));
String hexNumber = "100000";
System.out.println("Hexadecimal number " + hexNumber + " is equal to decimal number " + toDecimal(hexNumber));

The output for the toHex() method should match the input of the toDecimal() method.