无需预制语法将十六进制字符串转换为 integer 值

Question

I'm taking a computer organization class in college and I was tasked with writing a java program that takes a user inputted string, calls a function that converts said string into a hexadecimal integer, and then output the results.

The kicker is I can't use any existing syntax that will do this. for example, Integer.parseInt(__,16) or printf. It all neds to be hardcoded.

Now I'm not asking for you to do my homework for me, Just wanting to be put in the right direction.

So far, I've made this but can't seem to get the method created right:

import java.util.*;

public class Demo_Class {

public static void main(String[] args) 
{
    Scanner AI = new Scanner(System.in);
    String str;
    
    System.out.println("Please input a hexadecimal number: ");
    str = AI.nextLine();
    
    converter(str);
}
    

public static int converter(String in)
{
    String New = new String();
    for(int i = 0; i<= in.length(); i++)
    {
        New += in.charAt(i);
        System.out.println(New + 316);
    }
    
    return 0;
}

}

Answer 1

@WJS gave a good hint, I'd just like to add that the charAt() returns the char , which is encoded in ASCII.

As you can see in the ASCII table , the characters AF have decimal values from 65 to 70, while 0-9 go from 48 to 57 so you'll need to use them to convert the ASCII characters to their intended value.

To do so, you can either get the decimal value of a character by casting to short like short dec = (short)in.charAt(i); , or directly use the characters like char current = in.charAt(i) - 'A' .

With this in mind, all that's left is some calculation, I'll leave that as the homework. :)

Also:

• you are looping one character more than needed, change the i <= in.length() to i < in.length() , since it's going from 0
• I don't know what that 316 "magic number" is, if it does mean something, declare a variable with a meaningful name, like:

final int MEANINGFUL_NAME = 316;

Answer 2

Consider this, lets says you have the hex value 1EC which in hex digits would be 1, E, C . In decimal they would be 1, 14, 12 .

so set sum = 0.

• sum = sum*16 + 1. sum is now 1
• sum = sum*16 + 14 sum is now 30
• sum = sum*16 + 12 sum is now 492

So 492 is the answer.

If you have a string of 1EC you need to convert to characters and then convert those characters to the decimal equivalent of hex values.

Try this on paper until you get the feel and then code it. You can check your results using the Integer method you mentioned.