Converting binary string to a hexadecimal string JAVA

Question

I want to convert my binary(which is in string) to hexadecimal string also, this is just a program fragment since this program is just a part of another bigger program:

//the variable name of the binary string is: "binary"
int digitNumber = 1;
    int sum = 0;
    int test = binary.length()%4;
    if(test!=0) {
        binary = padLeft(binary, test);
    }
    for(int i = 0; i < binary.length(); i++){
        if(digitNumber == 1)
            sum+=Integer.parseInt(binary.charAt(i) + "")*8;
        else if(digitNumber == 2)
            sum+=Integer.parseInt(binary.charAt(i) + "")*4;
        else if(digitNumber == 3)
            sum+=Integer.parseInt(binary.charAt(i) + "")*2;
        else if(digitNumber == 4 || i < binary.length()+1){
            sum+=Integer.parseInt(binary.charAt(i) + "")*1;
            digitNumber = 0;
            if(sum < 10)
                System.out.print(sum);
            else if(sum == 10)
                System.out.print("A");
            else if(sum == 11)
                System.out.print("B");
            else if(sum == 12)
                System.out.print("C");
            else if(sum == 13)
                System.out.print("D");
            else if(sum == 14)
                System.out.print("E");
            else if(sum == 15)
                System.out.print("F");
            sum=0;
        }
        digitNumber++;  
    }
    public static String padLeft(String s, int n) {
        return String.format("%0$"+n+"s", s);
    }//i added this for padding

the problem is that i dont know if the padding works but i am sure that this program return a wrong hexadecimal conversion of the binary string I am trying to do this:

http://www.wikihow.com/Convert-Binary-to-Hexadecimal

PS: I need to implement it(not using any built-in function)

Answer 1

If you don't have to implement that conversion yourself, you can use existing code :

int decimal = Integer.parseInt(binaryStr,2);
String hexStr = Integer.toString(decimal,16);

If you must implement it yourself, there are several problems in your code :

1. The loop should iterate from 0 to binary.length()-1 (assuming the first character of the String represents the most significant bit).
2. You implicitly assume that your binary String has 4*x charcters for some integer x. If that's not true, your algorithm breaks. You should left pad your String with zeroes to get a String of such length.
3. sum must be reset to 0 after each hex digit you output.
4. System.out.print(digitNumber); - here you should print sum, not digitNumber.

Here's how the mostly fixed code looks :

    int digitNumber = 1;
    int sum = 0;
    String binary = "011110101010";
    for(int i = 0; i < binary.length(); i++){
        if(digitNumber == 1)
            sum+=Integer.parseInt(binary.charAt(i) + "")*8;
        else if(digitNumber == 2)
            sum+=Integer.parseInt(binary.charAt(i) + "")*4;
        else if(digitNumber == 3)
            sum+=Integer.parseInt(binary.charAt(i) + "")*2;
        else if(digitNumber == 4 || i < binary.length()+1){
            sum+=Integer.parseInt(binary.charAt(i) + "")*1;
            digitNumber = 0;
            if(sum < 10)
                System.out.print(sum);
            else if(sum == 10)
                System.out.print("A");
            else if(sum == 11)
                System.out.print("B");
            else if(sum == 12)
                System.out.print("C");
            else if(sum == 13)
                System.out.print("D");
            else if(sum == 14)
                System.out.print("E");
            else if(sum == 15)
                System.out.print("F");
            sum=0;
        }
        digitNumber++;  
    }

Output :

7AA

This will work only if the number of binary digits is divisable by 4, so you must add left 0 padding as a preliminray step.