Converting some hexadecimal string to a 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 a letter) I got an error like this:

java.lang.NumberFormatException: For input string: " 100a" at java.lang.NumberFormatException.forInputString(Unknown Source) at java.lang.Integer.parseInt(Unknown Source)

How can I convert my string with letters to a decimal integer?

if(display.getText() != null)
{
    if(display.getText().contains("a") || display.getText().contains("b") ||
       display.getText().contains("c") || display.getText().contains("d") ||
       display.getText().contains("e") || display.getText().contains("f"))
    {
        temp1 = Integer.parseInt(display.getText(), 16);
        temp1 = (double) temp1;
    }
    else
    {
        temp1 = Double.parseDouble(String.valueOf(display.getText()));
    }
}

Solution 1

It looks like there's an extra (leading) space character in your string (" 100a"). You can use trim() to remove leading and trailing whitespaces:

temp1 = Integer.parseInt(display.getText().trim(), 16);

Or if you think the presence of a space means there's something else wrong, you'll have to look into it yourself, since we don't have the rest of your code.

Solution 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 on the Internet. Some of the other solutions provided here didn't always work for me.

Solution 3

//package com.javatutorialhq.tutorial;

import java.util.Scanner;

/* Java code to 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 hexadecimal 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 hexadecimal number

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

        finally {
            s.close();
        }
    }
}

Solution 4

My way:

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

Solution 5

Since there is no brute-force approach which (done with it manualy). To know what exactly happened.

Given a hexadecimal number

KₙKₙ₋₁Kₙ₋₂....K₂K₁K₀

The equivalent decimal value is:

Kₙ * 16ₙ + Kₙ₋₁ * 16ₙ₋₁ + Kₙ₋₂ * 16ₙ₋₂ + .... + K₂ * 16₂ + K₁ * 16₁ + K₀ * 16₀

For example, the hex number AB8C is:

10 * 16₃ + 11 * 16₂ + 8 * 16₁ + 12 * 16₀ = 43916

Implementation:

 //convert hex to decimal number
private static int hexToDecimal(String hex) {
    int decimalValue = 0;
    for (int i = 0; i < hex.length(); i++) {
        char hexChar = hex.charAt(i);
        decimalValue = decimalValue * 16 + hexCharToDecimal(hexChar);
    }
    return decimalValue;
}
private static int hexCharToDecimal(char character) {
    if (character >= 'A' && character <= 'F')
        return 10 + character - 'A';
    else //character is '0', '1',....,'9'
        return character - '0';
}

View more solutions

Comments

[stevevls]

Don't forget that hex is case insensitive, so you should check for capital A-F as well.

[scottb]

It is dangerous to conclude that only numbers with hex digits "a" thru "f" are hexadecimal. It is quite possible for a hexadecimal value to not contain any of these digits at all.

[Peter Mortensen]

There is a lot of redundancy in it (and inefficiency). display.getText() is repeated 12 times.

[Peter Mortensen]

This question is now attracting answers that reinvent the wheel (only the title of the question is read before answering). This question already uses Integer.parseInt(display.getText(), 16); for the conversion!!!!

[Kevin Bowersox]

Good catch! Never would have seen that.

[Joaquin Iurchuk]

Doesn't work for me. I tried to passing it the String number 0a470c00025f424a. Even I tried to return long instead of int

[NonameSL]

In the for loop, just loop through each char in s.toCharArray(). I checked, it's quicker.

[Sunil Garg]

Please provide some explanation

[Deepu]

I simplify the solution.

[Peter Mortensen]

That is a lot of redundancy. Isn't there an easier way?

[Peter Mortensen]

What do you mean by "didn't always work for me"? For upper and lower case hexadecimal notation ('a'-'f' and 'A'-'F' )?

[Peter Mortensen]

That doesn't seem credible. It seems like a completely bogus answer. Can you explain your solution, please (including linking to documentation)? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[Peter Mortensen]

That is a lot of redundancy. Isn't there an easier way?

[Peter Mortensen]

But it doesn't answer the question. Sample input was string "100a" and "625b".

[Peter Mortensen]

But that is already used in the question. The real problem was the leading space in the string (solved 3 1/2 years prior).

[Peter Mortensen]

But the question was not about implementing the conversion. That is already in Java (the question used Integer.parseInt(hex, 16).)

[Peter Mortensen]

But the question was not about implementing the conversion. That is already in Java (the question used Integer.parseInt(hex, 16).). And it doesn't answer the question. Sample input was string "100a" and "625b".

[Peter Mortensen]

But the question was not about implementing the conversion. That is already in Java (the question used Integer.parseInt(hex, 16).).

[Peter Mortensen]

But the question was not about implementing the conversion. That is already in Java (the question used Integer.parseInt(hex, 16).).

[Peter Mortensen]

What is BigInteger? At least link to the documentation (as a non-naked link). Part of some library? Built-in? What is the minimum Java version? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[Stefan Emanuelsson]

@PeterMortensen BigInteger is standard java. Find yourself a better hobby

[AlexAndro]

@PeterMortensen Impossible to remember at this moment, have passed 7 years :) I suppose for some inputs did not get always the expected output.