Hexed by converting ints to hex

Java's Integer class includes two methods for converting values into Strings. There's a general one:

    /**
     * Converts the specified integer into a string representation based on the
     * specified radix.
     */
    public static String toString(int i, int radix) { ... }

Plus there's also methods for commonly used bases:

    /**
     * Converts the specified integer into its hexadecimal string
     * representation.
     */
    public static String toHexString(int i) { ... }

    /**
     * Converts the specified integer into its octal string representation.
     */
    public static String toOctalString(int i) { ... }

    /**
     * Converts the specified integer into its binary string representation.
     */
    public static String toBinaryString(int i) { ... }

My expectation was that the first was simply a more general form. Given this assumption, I expected the following program to print the same three lines twice:

  public static void main(String... args) {
    System.out.println(Integer.toHexString(0xCAFE));
    System.out.println(Integer.toHexString(0xBABE));
    System.out.println(Integer.toHexString(0xCAFEBABE));
    System.out.println(Integer.toString(0xCAFE, 16));
    System.out.println(Integer.toString(0xBABE, 16));
    System.out.println(Integer.toString(0xCAFEBABE, 16));
  }

But it turns out that negative numbers have slightly surprising results when combined with arbitrary bases. The program prints the following:

cafe
babe
cafebabe
cafe
babe
-35014542

If you're emitting hex or binary data, you probably should avoid toString(int value, int radix).

# posted by Jesse Wilson on Tuesday, December 15, 2009