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A "trivial" (easy to understand but not practical) conversion function

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• A trivial conversion method to convert 2's complement numbers to string (ASCII) representation
  • Before discussing the parseInt( ) method, I want to show you what this method need to do by using a trivial solution.

    There is a 1-to-1 correspondence between 2's complement representation of numbers and its String representation:

    2's complement representation (32 bits) String representation ---------------------------------- ----------------------- 00000000000000000000000000000000 "0" 00000000000000000000000000000001 "1" 00000000000000000000000000000010 "2" 00000000000000000000000000000011 "3" ... ... 11111111111111111111111111111111 "-1" 11111111111111111111111111111110 "-2" 11111111111111111111111111111101 "-3" ... ...

  • You can convert a 2's complement binary number into its number string by testing every possible integer input and return the corresponding string representation as follows:

    public static String toString( int x ) { if ( x == 0 ) // Compares x against 00000000000000000000000000000000 return "0"; // Returns the ASCII code for string "0" ! else if ( x == 1 ) return "1"; else if ( x == 2 ) return "2"; ... else if ( x == 10 ) return "10"; else if ( x == 11 ) return "11"; ... else if ( x == -1 ) return "-1"; else if ( x == -2 ) return "-2"; ... }

  • This method is not practical because you will need to write 2³² (= 4294967296) different cases with the if-statements !!!

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• Dictatical comment
  • I want to pause a bit and make sure that you know that:

    When you write this expression in Java: x == 5; // Or some other decimal number (it's used in the above program), the Java compiler will generate computer instructions that will: compare x with 5 as a 2's complement binary number, i.e.: it compares with 00000000000000000000000000000101