Interactive Input/Output

1. Interactive Input/Output Contents • Reading data from the keyboard • Extracting separate data items from a String • Converting from a String to a primitive numerical type • An example showing how numerical data is read from the keyboard and used to obtain and display a result • Using dialog boxes to obtain input data and display results

2. Keyboard Input The System class in java provides an InputStream object: System.in And a buffered PrintStream object System.out The PrintStream class (System.out) provides support for outputting primitive data type values. However, the InputStream class only provides methods for reading byte values. To extract data that is at a “higher level” than the byte, we must “encase” the InputStream, System.in, inside an InputStreamReader object that converts byte data into 16-bit character values (returned as an int). We next “wrap” a BufferedReader object around the InputStreamReader to enable us to use the methods read( ) which returns a char value and readLine( ), which return a String.

3. BufferedReader InputStreamReader byte int string Keyboard Input import java.io.*; //for keyboard input stream InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); String st = br.readLine( ); //reads chars until eol and forms string

4. 6 2 4 3 2 1 String Tokenizer Consider the following program fragment: import java.io.*; publicclass TotalNumbers throws java.io.IOException{ privateString str; privateint num; publicstaticvoid main (String [] args) { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); System.out.print(“Enter four integers: “); str = br.readLine( ); str =

5. 6 2 4 3 2 1 String Tokenizer We need to retrieve the four separate integers from the string. str = A token consists of a string of characters separated by a delimiter. Delimiters consist of {space, tab, newline, return} A StringTokenizer parses a String and extracts the individual tokens. StringTokenizer st = new StringTokenizer (str); //create tokenizer and pass string String s_temp; while (st.hasMoreTokens( ) ) { s_temp = st.nextToken( ); //now convert this string to an integer.

6. Wrapper Classes For each of the primitive types there is a Wrapper class. Primitive type object int num1 = 6; Integer myInt = Integer(num1); double num2 = 3.1416; Double pi = Double(num2); In the statement Integer myInt = Integer(num1); an Integer object named myInt is created and assigned a value equal to the contents of num1 Wrapper classes begin with an uppercase letter to distinguish from their primitive type counterpart (int, long, short, double, float, byte, char, boolean). int  Integer double  Double float  Float char  Character

7. wrapper method name return type Wrapper Classes Unlike primitive types, objects have operations called methods that they can be directed to perform. (These methods have visibility static they can be accessed by using the class name without instantiating objects of the class. Wrapper class objects have a method for converting a string into a primitive type, and a method for transforming a primitive type into a string. Integer parseInt(String st) int Integer toString(int num) String Double parseDouble(String st) double Double toString(double num) String Float parseFloat(String st) float Long parseLong(String st) long

8. Converting Tokenized String to Primitive Types Return to the code for extracting tokens from the input string int sum = 0, num; String s; while (st.hasMoreTokens( )) { s = st.nextToken( ); //convert string to int num = Integer.parseInt(s); sum += num; }

9. Review -- Reading stream of integers from keyboard Step 1 – Prompt user to enter multiple integers on one line System.out.print(“Enter four integers separated by spaces: “); Step 2 – Retrieve keyboard input as a stream of 16-bit chars (retuned as int) InputStreamReader isr = new InputStreamReader(System.in); Step 3 – Form input stream of characters into a string (look for eol) BufferedReader br = new BufferedReader(isr); String str = br.readLine( ); Need to throw java.io.IOException in function in which it is used Step 4 – Create StringTokenizer to extract tokens from the input string StringTokenizer st = new StringTokenizer(str);

10. Review – cont. Step 5 – Parse the input string to extract tokens String s1 = st.nextToken( ); //note can use while(st.hasMoreTokens( )) to repeatedly extract each //token in the string Step 6 – Use wrapper class methods to convert token (string) to primitive type int num = Integer.parseInt(s1);

11. Putting it all together import java.io.*; //for keyboard input methods import java.util.*; //for StringTokenizer publicclass TotalNumbers { publicstaticvoid main (String [] args) throws java.io.IOException { String str, s; int sum = 0, num; InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); System.out.print(“Enter four integers separated by spaces: “); //prompt str = br.readLine( ); StringTokenizer st = new StringTokenizer(str); while (st.hasMoreTokens( )) { s = st.nextToken( ); num = Integer.parseInt(s); sum += num; } } }

12. Input x the message ? Interactive Input Using a Dialog box to request input data Step 1 – Import swing package. import javax.swing.*; Step 2 – Create an input dialog box (returns a String) String str = JOptionPane.showInputDialog(“the message”); Input OK Cancel Step 3 – Write input value(s) in the text field //done by user Step 4 – Click on command button (OK, Cancel) //done by user

13. ! ? Output to a Dialog Box Types of Dialog Boxes icon WARNING_MESSAGE QUESTION_MESSAGE INFORMATION_MESSAGE ERROR_MESSAGE PLAIN_MESSAGE

14. greetings X Hi Mom! OK Output Dialog Boxes To create a dialog box for displaying output use showMessageDialog JOptionPane.showMessageDialog(null, “message”, “title”,icon_type); For example, the statement: JOptionPane.showMessageDialog(null, “Hi Mom!”, “greetings”, JOptionPane.PLAIN_MESSAGE); produces

15. Output Dialog Boxes Note that the icon-type field in the showDialogMessage( ) method is a static constant declared in class JOptionPane, and must be referenced by a message to this class. JOptionPane.PLAIN_MESSAGE The icon_type determines which of the five icons (the fifth being no icon at all) will appear in the dialog box. Note! Without the final statement System.exit(0); a program that ends with a message dialog box will still be active after the dialog box has been closed.

16. An Interactive Program that Uses Dialog Boxes import javax.swing.*; //for JOptionPane import java.util.*; //for StringTokenizer publicclass DialogExample { publicstaticvoid main(String [] args) { String sInput, str; int num, sum = 0; sInput = JOptionPane.showInputDialog(“enter three integers: “); StringTokenizer st = new StringTokenizer(sInput); while (st.hasMoreTokens( ) ) { str = st.nextToken( ); num = Integer.parseInt(str); sum += num; } //output the result to a dialog box JOptionPane.showDialogMessage(null, “DialogExample Output”, “the sum is: ”+ sum, JOptionPane.INFORMATION_MESSAGE); System.exit(0); //needed to close program when using dialog box } }

17. Review To perform interactive I/O using dialog boxes 1. import javax.swing.*; • Use an input dialog box to prompt the user to enter data (returns a String) • String inString = JOptionPane.showInputDialog(“your message”); • Use a StringTokenizer (if necessary) to extract the individual tokens • from the input String • Convert (String) tokens into primitive types wherever necessary using • the appropriate wrapper class. • Use a dialog box to display the output • JOptionPane.showMessageDialog(null,”message”, “title”, icon-type): • When using a Message dialog box, end the program with • System.exit(0);