Converter.java

Below is the syntax highlighted version of Converter.java from §5.1 Data Representations.

/*************************************************************************
 *  Compilation:  javac Converter.java
 *  Execution:    java Converter
 *  
 *  Converts an integer to and from its base b representation.
 *  No error checking is currently implemented.
 *
 *  Remarks
 *  -------
 *   - See also Integer.toHexString(), Integer.toString(int i, int radix)
 *   - See also Integer.parseInt(String s, int radix)
 *
 *************************************************************************/

public class Converter { 

   // converts integer n into a base b string
    static String toString(int n, int base) {
       // special case
       if (n == 0) return "0";

       String digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
       String s = "";
       while (n > 0) {
          int d = n % base;
          s = digits.charAt(d) + s;
          n = n / base;
       }
       return s;
    }

    static String toBinaryString(int n) { return toString(n,  2); }
    static String toHexString(int n)    { return toString(n, 16); }


    static void inputError(String s) {
        throw new RuntimeException("Input error with" + s);
    }

    // convert a String representing a base b integer into an int
    static int fromString(String s, int b) {
       int result = 0;
       int digit = 0;
       for (int i = 0; i < s.length(); i++) {
          char c = s.charAt(i);
          if (c >= '0' && c <= '9')
             digit = c - '0';
          else if (c >= 'A' && c <= 'Z')
             digit = 10 + c - 'A';
          else inputError(s);

          if (digit < b) result = b * result + digit;
          else inputError(s);
       }
       return result;
    }

    static int fromBinaryString(String s) { return fromString(s,  2); }
    static int fromHexString(String s)    { return fromString(s, 16); }


    // sample test client
    public static void main(String[] args) {
        int n = 47;
        String s = "101111";
        System.out.println(n +  ":  " + toBinaryString(n));
        System.out.println(s +  ":  " + fromBinaryString(s));
        System.out.println(n +  ":  " + toHexString(n));
        System.out.println();

        n = 2620;
        s = "0A3C";
        System.out.println(n +  ":  " + toBinaryString(n));
        System.out.println(s +  ":  " + fromHexString(s));
        System.out.println(n +  ":  " + toHexString(n));
    }
}