1. Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

2. Objectives You should be able to describe: Interactive Keyboard Input
Interactive Dialog Input
Creating a Class Library
Formatted Output
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

3. Objectives (continued)
Mathematical Methods
Common Programming Errors
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

4. Interactive Keyboard Input
Interactive data is entered:
By user at keyboard
Via graphical user interface (GUI)
From file
Data can be entered into program while it is running using System.in object
Stream objects
Called streams for short
Transmit data as stream of individual data bytes
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

5. Interactive Keyboard Input (continued)
End-of-file (EOF) marker
Special end-of-data value
Numerical value that cannot be converted into legitimate character value
Would like to read an entire line at once
Use supporting classes:
InputStreamReader
BufferedReader
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

6. Interactive Keyboard Input (continued)
Figure 4.2: Generating the EOF value
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

7. Interactive Keyboard Input (continued)
InputStreamReader
Automatically converts integer values of System.in stream to character values
Can be constructed from System.in object
InputStreamReader isr =
new InputStreamReader(System.in);
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

8. Interactive Keyboard Input (continued)
BufferedReader
Automatically constructs string from character values provided by InputStreamReader object
BufferedReader br = new BufferedReader(isr);
Display prompt
Asks user to enter data
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

9. Interactive Keyboard Input (continued)
Calling readLine()
Puts system in wait state
Until user types data
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

10. Interactive Keyboard Input (continued)
Table 4.1: Keyboard Input Classes and Methods
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

11. Interactive Keyboard Input (continued)
Table 4.2: Java Conversion Routines
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

12. The StringTokenizer Class
String of characters separated by delimiting character
Delimiting characters
Whitespace by default in Java
Parsing the string
Separating individual tokens from string
Class StringTokenizer
Used to parse strings
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

13. The StringTokenizer Class (continued)
Figure 4.5: Parsing tokens from a string
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

14. The Scanner Class Provides simpler way to read numerical input
No need to perform data type conversion
Example:
Scanner sc = new Scanner(System.in);
double num1 = sc.nextDouble();
java.util.Formatter class
Process more complex input
Includes pattern matching algorithms
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

15. The Scanner Class (continued)
Table 4.3: Commonly Used Scanner Class Input Methods
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

16. A First Look at User-Input Validation
Well-constructed program
Validates user input
Does not crash due to unexpected input
Crash
Program termination caused by unexpected error
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

17. A First Look at User-Input Validation (continued)
Figure 4.6: A NumberFormatException notification
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

18. A First Look at User-Input Validation (continued)
Consists of:
Validating entered data either during or immediately after data have been entered
Providing user with way of reentering any invalid data
To handle invalid input provide error processing code
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

19. A First Look at User-Input Validation (continued)
Throwing error up to operating system
Use reserved word throws with error name
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

20. Interactive Dialog Input
GUI method of entering user data:
Method named showInputDialog()in JOptionPane class
Creates dialog box that permits user to enter string
Syntax:
JOptionPane.showInputDialog(string);
Example:
s = JOptionPane.showInputDialog("Enter number:");
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

21. Interactive Dialog Input
Figure 4.7: A sample showInputDialog() dialog
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

22. Exception Handling
Error handling in Java different from other high-level languages
Exception handling
Error occurs while method is running
Method creates object that contains information about error
Object immediately passed to Java Virtual Machine
JVM attempts to locate code to handle exception
Called throwing an exception
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

23. Exception Handling (continued)
Two fundamental types of errors:
Result from inability of program to obtain required resource
Result from flawed code
Checked exception
Java checks that exceptions will be handled
Program must throw or handle exception
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

24. Exception Handling (continued)
Unchecked exception
Java compiler does not check for handling code
Error can always be prevented by programming
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

25. Exception Handling (continued)
Figure 4.4: Exception Handling Terminology
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

26. Exception Handling (continued)
try {
// one or more statements }
catch (exceptionName argument)
finally
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

27. Exception Handling (continued)
try
Identifies start of exception handling block of code
Must be followed by one or more catch blocks
catch
Exception handler code
finally
Default set of instructions always executed whether or not any exception occurred
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

28. Creating a Class Library
Java provides extensive set of tested and reliable classes
Increases with introduction of each new version
Professional programmers create and share own libraries of classes
Once they are tested
Can be reused in other programs
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

29. Formatted Output
Display of both integer and floating-point numbers can be controlled by Java-supplied format() method
In class java.text.DecimalFormat
Especially useful in printing columns with numbers
Example:
DecimalFormat num = new DecimalFormat("000");
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

30. Formatted Output (continued)
Required components for formatted output:
Import statement for java.text package of classes
Statement within main() method that uses new operator to create desired format string
format() method call that applies format string to numerical value
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

31. Formatted Output (continued)
Table 4.5: Symbols for User-Defined Format Strings
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

32. Formatted Output (continued)
Table 4.6: Examples of Numerical Formats
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

33. Formatted Output using printf
Method of PrintStream class
Syntax:
printf(control string, arguments)
Example:
printf("The value of 6 plus 15 is %d%n", );
Conversion control sequence
Begins with % symbol
Ends with conversion character
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

34. Formatted Output using printf (continued)
Table 4.7: Common Conversion Sequences for printf
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

35. Width and Precision Specifiers
Optional specifications for numbers:
Field width
Precision
Example:
System.out.printf("|%10.3f|", 25.67);
Width: 10
Precision: 3
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

36. Width and Precision Specifiers (continued)
Table 4.8: Effect of Field Width and Precision Specifiers
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

37. Flags Justification Explicit sign display printf format
Normally right-justified for numbers
Use – flag to left-justify
Explicit sign display
Normally displayed only for negative numbers
Use + flag to display for all numbers
printf format
%[flags] [width] [precision] conversionCharacter
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

38. Mathematical Methods
Java provides standard preprogrammed methods within class named Math
Methods are static and public
Each Math class method is called by:
Listing name of class
A period
Method’s name
Passing data within parentheses following method’s name
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

39. Mathematical Methods (continued)
Table 4.9: Java’s Math Class Methods
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

40. Mathematical Methods (continued)
Figure 4.17: Using and passing data to a Math class method
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

41. Casts Java provides for explicit user-specified type conversions
Use cast operator
Unary operator
Syntax:
(dataType) expression
Example:
(int) (a * b)
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

42. Conversion Methods
Routines for converting string to primitive type and primitive type to string
Referred to as wrapper classes
Class structure wrapped around built-in:
integer
long
float
double
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

43. Conversion Methods (continued)
Table 4.11: Wrapper Class Conversion Routines
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

44. Conversion Methods (continued)
Figure 4.18: Conversions using a wrapper class method
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

45. Common Programming Errors
Forgetting to precede mathematical method with class name Math and period
Not understanding difference between writing program for personal use and one intended for someone else’s use
Being unwilling to test program in depth that is to be used by people other than yourself
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

46. Summary Input from keyboard accomplished using readLine() method
Must create InputStreamReader and BufferedReader
Input dialog box method used for data input
From class JOptionPane
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition

47. Summary (continued) Exception Java provides Math class
Error condition that occurs when program running
Notification of exception immediately sent to Java Virtual Machine for processing
Java provides Math class
Contains methods for mathematical computations
Java String class provides methods for converting strings into primitive numerical types
Object-Oriented Program Development Using Java: A Class-Centered Approach, Enhanced Edition