A Guide Illustrating the Core Java Equivalent to Selected Tasks Done Using the HSA Class Library

Transcription

1 HSA to Core Java A Guide Illustrating the Core Java Equivalent to Selected Tasks Done Using the HSA Class Library The examples below compare how tasks are done using the hsa Console class with how they are done using core Java commands only. For all examples in the HSA column, there must be a Console object called c already declared and instantiated. This code is not included in the examples. In the Standard Java Classes column, all required lines of code are shown, including any necessary object declarations and instantiations. Standard Output When using the c.print and c.println commands included in the HSA Console class, the output appears in a Console Window. This window has graphic capabilities (pixel drawing methods), as well as built-in methods for formatted output, and has buttons for saving or printing output. When the core java commands System.out.print and System.out.println commands are used, the output appears in a plain DOS console window. This window is text only, has no built-in formatted output capabilities, and has no buttons to control saving and printing output (these functions must be handled through command line arguments). Language HSA Standard Java Classes Output c.println( Hello ); c.print( Goodbye ); c.println(54); System.out.println( Hello ); System.out.print( Goodbye ); System.out.println(54);

2 Text When getting (non-numerical) text input from the keyboard, the readline( ) method can always be used. This method will read in an entire line of input from the keyboard (including spaces). When using the HSA package, the readline( ) method is part of Console class. To access the readline function, simply precede it by the name of the Console object, c. When using the core java classes only, the readline( ) method is used from a BufferedReader object. When instantiating the BufferedReader object, we must indicate that the input will be from the keyboard (as opposed to a file or some other source). This is done by using the line of code and then using the newly formed object (isr) in the instantiation of the buffered reader object. Note that the line of code textline = stdin.readline( ); could possible fail and cause an error or exception (for example, if the user entered too much text to be stored in the String textline). When using the Console class, we do not have to worry about this. When using readline( ) from the BufferedReader class however, we must warn the compiler that an exception might occur. We do this by adding throws IOException to the opening line of the method in which the readline( ) is located. For example, if the code is located in the main method, the line of code public static void main (String [] args) would become: public static void main (String [] args) throws IOException. Alternately, the line of code containing readline( ) could be placed in a try-catch structure. In this case, textline = stdin.readline( ); would become: try { textline = stdin.readline( ); } catch (Exception ee) { ; }

3 Language HSA Standard Java Classes Text c.print("enter a line of text: "); textline = c.readline(); c.println("\n\nthe line of text entered was: " + textline); System.out.print("Enter a line of text: "); textline = stdin.readline(); System.out.println("\n\nThe line of text entered was: " + textline); Note that there is no core java equivalent of the c.readstring( ) method (which only returns the first token entered instead of the entire line of text). The entire line must be stored, and then broken down into tokens using the StringTokenizer class. The reader should also be aware that there has been another way of getting text input using the core java classes only. Although this method is deprecated (discontinued), it may be encountered when reading java code, books, or websites. In this deprecated way of getting the text input, the readline( ) method is used from a DataStream object: DataStream stdin = new DataStream(System.in); System.out.print("Enter a line of text: "); textline = stdin.readline(); System.out.println("\n\nThe line of text entered was: " + textline);

4 Numerical When using the HSA Console, we can get numerical input directly from the keyboard using the readint( ), and the readdouble( ) functions. The values returned by these functions can be stored directly into a variable of type int or double respectively. When using the core java classes only, there is neither a readint( ) nor a readdouble( ) function available for use. Instead, the input must first be stored into a String using the readline( ) method. Next, the resulting String is converted to an int or double, and finally stored in a variable of the proper type. The type conversion from String to integer must be done by the static method called parseint (from the Integer class). Similarly, the type conversion from String to double must be done by the static method called parsedouble (from the Double class). Note that the type conversions could possibly fail (for example if the user enters a name when asked for an integer). We must add the code throws IOException to the opening line of the method (as shown before), or, place the lines of code that do the type conversion in a try-catch structure. Language HSA Standard Java Classes Integer c.print("enter an integer: "); myint = c.readint(); System.out.print("Enter an integer: "); myint = Integer.parseInt(tempString); c.println("\n\nthe integer entered was: " + myint); System.out.println("\n\nThe integer entered was: " + myint);

5 Real Number c.print("enter an real number : "); myrealnumb = c.readdouble(); System.out.print("Enter an real number (ie: a double): "); myrealnumb = Double.parseDouble(tempString); c.println("the real number input was: " +RealNumb); System.out.println("The real number entered was: " + myrealnumb); hsa - core java dictionary compiled by William R. Duncan

6 HSA to Core Java Quick Guide A Guide Illustrating the Core Java Equivalent to Selected Tasks Done Using the HSA Package HSA Standard Java Classes Output c.println( Hello ); c.print( Goodbye ); c.println(54); System.out.println( Hello ); System.out.print( Goodbye ); System.out.println(54); <add throws IOException to end of the opening line of the method> Text c.print("enter a line of text: "); textline = c.readline(); c.println("the line of text entered was: " + textline); System.out.print("Enter a line of text: "); textline = stdin.readline(); System.out.println("The line of text entered was: " + textline); Integer c.print("enter an integer: "); myint = c.readint(); c.println("\n\nthe integer entered was: " + myint); <add throws IOException to end of the opening line of the method> System.out.print("Enter an integer: "); myint = Integer.parseInt(tempString); System.out.println("\n\nThe integer entered was: " + myint); Real Number c.print("enter an real number : "); myrealnumb = c.readdouble(); c.println("the real number input was: " +RealNumb); <add throws IOException to end of the opening line of the method> System.out.print("Enter an real number (ie: a double): "); myrealnumb = Double.parseDouble(tempString); System.out.println("The real number entered was: " + myrealnumb); hsa - core java dictionary compiled by William R. Duncan