Converting Hexadecimal String to Decimal Integer

Question

I wrote some code to convert my hexadecimal display string to decimal integer. However, when input is something like 100a or 625b( something with letter) I got an error like

Answer 1

This is my solution:

public static int hex2decimal(String s) {
    int val = 0;
    for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);
        int num = (int) c;
        val = 256*val + num;
    }
    return val;
}

For example to convert 3E8 to 1000:

StringBuffer sb = new StringBuffer();
sb.append((char) 0x03);
sb.append((char) 0xE8);
int n = hex2decimal(sb.toString());
System.out.println(n); //will print 1000.

Answer 2

  public static int hex2decimal(String s) {
             String digits = "0123456789ABCDEF";
             s = s.toUpperCase();
             int val = 0;
             for (int i = 0; i < s.length(); i++) {
                 char c = s.charAt(i);
                 int d = digits.indexOf(c);
                 val = 16*val + d;
             }
             return val;
         }

That's the most efficient and elegant solution I have found over the internet. Some of the others solutions provided here didn't always work for me.

Answer 3

This is a little library that should help you with hexadecimals in Java: https://github.com/PatrykSitko/HEX4J

It can convert from and to hexadecimals. It supports:

• byte
• boolean
• char
• char[]
• String
• short
• int
• long
• float
• double (signed and unsigned)

With it, you can convert your String to hexadecimal and the hexadecimal to a float/double.

Example:

String hexValue = HEX4J.Hexadecimal.from.String("Hello World");
double doubleValue = HEX4J.Hexadecimal.to.Double(hexValue);

Answer 4

You could take advantage of ASCII value for each letter and take off 55, easy and fast:

int asciiOffset = 55;
char hex = Character.toUpperCase('A');  // Only A-F uppercase
int val = hex - asciiOffset;
System.out.println("hexadecimal:" + hex);
System.out.println("decimal:" + val);

Output:
hexadecimal:A
decimal:10

Answer 5

My way:

private static int hexToDec(String hex) {
    return Integer.parseInt(hex, 16);
}

Answer 6

//package com.javatutorialhq.tutorial;

import java.util.Scanner;

/* * Java code convert hexadecimal to decimal */ 
public class HexToDecimal {

    public static void main(String[] args) {

        // TODO Auto-generated method stub 

        System.out.print("Hexadecimal Input:");

        // read the hexadecimal input from the console 

        Scanner s = new Scanner(System.in); 

        String inputHex = s.nextLine();

        try{ 

// actual conversion of hex to decimal

            Integer outputDecimal = Integer.parseInt(inputHex, 16);

            System.out.println("Decimal Equivalent : "+outputDecimal);


        }

        catch(NumberFormatException ne){

            // Printing a warning message if the input is not a valid hex number

            System.out.println("Invalid Input"); 

        }

        finally{ s.close();

        }
    } 
}