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How computers print out Boolean outputs

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• Problem description: how to display/show Boolean values to the user ?
  • Recall that:

    The Boolean value false is represented by the binary number 00000000 The Boolean value true is represented by the binary number 00000001           (See: click here )

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  • Boolean inputs are printed out (shown) to the user(s) by displaying the text:

    true or: false

    Problem:

    When the computer sends the Boolean values true (or false) to the terminal, it will send this code: 00000001 (or 00000000 (false)) The terminal cannot display the ASCII code 00000001 which is an unprintable character (Start of Heading) The terminal will not display the text true for the Boolean value to the user !!!

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  • In other words:

    Internally (= inside a Java program), the boolean valuem true is represented by the binary number 00000001 When the computer sends the binary number 00000001 to the terminal, the terminal will display an unprintable character - because the code 00000001 represents "Start of Header" in ASCII. In order for the terminal to display the text "true", the computer must send these ASCII codes to the terminal: 01110100 01110010 01110101 01100101

    Therefore: we need to convert the internal boolean representation to their (ASCII) representation for output operation also

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• Converting from the internal boolean representation to its ASCII representation
  • The Java class Boolean provides the toString( ) method to convert the internal "program" representation of the boolean values to their "ASCII" representation:

    String toString( boolean x ): return a String that represents the boolean value x If x == true, we return the string "true" If x == false, we return the string "false"

    See: click here

    The method toString( ) performs the following translation:

    Input Output ---------- ------------- 00000001 ---> "true" 00000000 ---> "false" Note: "true" means: the ASCII codes 01110100 01110010 01110101 01100101 "false" maens: the ASCII codes 01100110 01100001 01101100 01110011 01100101

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  • Example:

    boolean x = true; boolean y = false; String s; s = Boolean.toString(x); // Change to BooleanIO to use my own System.out.println("String for 'true' boolean value = " + s); s = Boolean.toString(y); // Change to BooleanIO to use my own System.out.println("String for 'false' boolean value = " + s);

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255001/demo/java/Bool2String.java

    How to run the program:

    To compile:   javac Bool2String.java          To run: java Bool2String

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• How to implement the Boolean.toString( ) method
  • The Boolean.toString( ) method is also very simple and I like to use it to show you a simple example of conversion between 2 different representations

    This is what the toString( ) method look like:

    public static boolean toString( boolean x ) { if ( x == true ) return "true"; // This is a String (= 4 ASCII codes !) else return "false"; // This is a String (= 5 ASCII codes !) }

    Note:

    The statement return "true" will return a string containing the ASCII codes for the characters 't' 'r' 'u' 'e' !!!

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  • Example Program: (Demo above code)                                                
    • Program file: /home/cs255001/demo/java/Bool2String.java

      Change Boolean to BooleanIO first !

    How to run the program:

    To compile:   javac Bool2String.java To run:          java Bool2String