CPIT 305 Advanced Programming

Transcription

1 M. G. Abbas Malik CPIT 305 Advanced Programming Assistant Professor Faculty of Computing and IT University of Jeddah

2 Advanced Programming Course book: Introduction to Java Programming: Comprehensive Edition, 10th Edition, Y. Daniel Liang, Pearson Reference BooK: Java How to Program, 9th Edition, Paul Deitel and Harvey Deitel, Deitel. Discrete Mathematics and its Application, Kenneth H. Rosen, 7th Edition, McGraw-Hill Java Docs: Course Home: 75% attendance is compulsory to sit in the final exam M. G. Abbas Malik, FCIT, UoJ 2

3 Advanced Programming Topics Covered Recursion Revisited Review of Object Oriented Concepts Exception Handling File and Stream Handling Binary I/O Multithreading and Parallel Programming Networking - Socket Programming Java Database Programming M. G. Abbas Malik, FCIT, UoJ 3

4 Exception Chapters: 12 Handling M. G. Abbas Malik, FCIT, UoJ 4

5 Exception handling enables a program to deal with exceptional situations and continue its normal execution M. G. Abbas Malik, FCIT, UoJ 5

6 ArrayIndexOutOfBoundsException If you access an array using an index that is out of bounds, you will get a runtime error with an ArrayIndexOutOfBoundsException int array[10]; // create 10 elements array array[10]; // Run time Error M. G. Abbas Malik, FCIT, UoJ 6

7 InputMismatchException If you enter a double value when your program expects an integer, you will get a runtime error with an InputMismatchException Scanner input = new Scanner(System.in); int x; // create an int x = input.nextint(); // Run time Error when users gives 2.34 M. G. Abbas Malik, FCIT, UoJ 7

8 Runtime errors are thrown as exceptions. An exception is an object that represents an error or a condition that prevents execution from proceeding normally. If the exception is not handled, the program will terminate abnormally. Exceptions are thrown from a method. The caller of the method can catch and handle the exception. M. G. Abbas Malik, FCIT, UoJ 8

9 Division by ZERO - Run Time Error/Exception LISTING 12.1 Quotient.java 1 import java.util.scanner; 2 3 public class Quotient { 4 public static void main(string[] args) { 5 Scanner input = new Scanner(System.in); 6 7 // Prompt the user to enter two integers 8 System.out.print("Enter two integers: "); 9 int number1 = input.nextint(); 10 int number2 = input.nextint(); System.out.println(number1 + " / " + number2 + " is " + (number1 / 13 number2)); 14 } 15 } M. G. Abbas Malik, FCIT, UoJ 9

10 Division by ZERO - Run Time Error/Exception LISTING 12.2 QuotientWithIf.java 1 import java.util.scanner; 2 3 public class QuotientWithIf { 4 public static void main(string[] args) { 5 Scanner input = new Scanner(System.in); 6 7 // Prompt the user to enter two integers 8 System.out.print("Enter two integers: "); 9 int number1 = input.nextint(); 10 int number2 = input.nextint(); if (number2!= 0) If Condition help us to avoid Division by ZERO Run Time Error/Exception 13 System.out.println(number1 + " / " + number2 + " is " + (number1 / number2)); 14 else 15 System.out.println("Divisor cannot be zero "); 16 } 17 } M. G. Abbas Malik, FCIT, UoJ 10

11 Division by ZERO - Run Time Error/Exception LISTING 12.3 QuotientWithMethod.java 1 import java.util.scanner; 2 3 public class QuotientWithMethod { 4 public static int quotient(int number1, int number2) { 5 if (number2 == 0) { 6 System.out.println("Divisor cannot be zero"); 7 System.exit(1); 8 } 9 10 return number1 / number2; 11 } public static void main(string[] args) { 14 Scanner input = new Scanner(System.in); // Prompt the user to enter two integers 17 System.out.print("Enter two integers: "); 18 int number1 = input.nextint(); 19 int number2 = input.nextint(); int result = quotient(number1, number2); 22 System.out.println(number1 + " / " + number2 + " is + result); 23 } 24 } M. G. Abbas Malik, FCIT, UoJ 11

12 Division by ZERO - Run Time Error/Exception LISTING 12.4 QuotientWithException.java 1 import java.util.scanner; 2 3 public class QuotientWithException { 4 public static int quotient(int number1, int number2) { 5 if (number2 == 0) 6 throw new ArithmeticException("Divisor cannot be zero"); 7 8 return number1 / number2; 9 } public static void main(string[] args) { 12 Scanner input = new Scanner(System.in); // Prompt the user to enter two integers 15 System.out.print("Enter two integers: "); 16 int number1 = input.nextint(); 17 int number2 = input.nextint(); 18 Handling Division by ZERO Run Time Error/Exception 19 try { 20 int result = quotient(number1, number2); 21 System.out.println(number1 + " / " + number2 + " is " 22 + result); 23 } 24 catch (ArithmeticException ex) { 25 System.out.println("Exception: an integer " + 26 "cannot be divided by zero "); 27 } System.out.println("Execution continues..."); 30 } 31 } M. G. Abbas Malik, FCIT, UoJ 12

13 Exception is an object created from an exception class - in Division by ZERO the exception is java.lang.arithmeticexception When an exception is thrown, the normal execution flow is interrupted. Throws and Exception: exception is passed from the point where it is occur to the point where the method is called - pass the exception from one place to another M. G. Abbas Malik, FCIT, UoJ 13

14 Division by ZERO - Run Time Error/Exception LISTING 12.4 QuotientWithException.java 1 import java.util.scanner; 2 3 public class QuotientWithException { 4 public static int quotient(int number1, int number2) { 5 if (number2 == 0) 6 throw new ArithmeticException("Divisor cannot be zero"); 7 8 return number1 / number2; 9 } public static void main(string[] args) { 12 Scanner input = new Scanner(System.in); // Prompt the user to enter two integers 15 System.out.print("Enter two integers: "); 16 int number1 = input.nextint(); 17 int number2 = input.nextint(); try { 20 int result = quotient(number1, number2); 21 System.out.println(number1 + " / " + number2 + " is " 22 + result); 23 } 24 catch (ArithmeticException ex) { 25 System.out.println("Exception: an integer " + 26 "cannot be divided by zero "); 27 } System.out.println("Execution continues..."); 30 } 31 } M. G. Abbas Malik, FCIT, UoJ 14

15 Try Catch Code Block - Handle Exception in an appropriate way and stop your program from crashing in the middle of execution try { Java Code to Run; A Statement or a method call that may throw an exception More Code to Run; } catch (ExceptionType identifier_variable) { Code to process the exception; } M. G. Abbas Malik, FCIT, UoJ 15

16 Try Catch Code Block - an exception can be thrown directly in the Try block using throw statement try { Java Code to Run; throw Exception ( It is an exception ); More Code to Run; } catch (ExceptionType identifier_variable) { Code to process the exception; } M. G. Abbas Malik, FCIT, UoJ 16

17 Try Catch Code Block - an exception may be thrown by the invoked method in Try block try { Java Code to Run; mymethod(); More Code to Run; } catch (ExceptionType identifier_variable) { Code to process the exception; } M. G. Abbas Malik, FCIT, UoJ 17

18 Division by ZERO - Run Time Error/Exception LISTING 12.4 QuotientWithException.java 1 import java.util.scanner; 2 3 public class QuotientWithException { 4 public static int quotient(int number1, int number2) { 5 if (number2 == 0) 6 throw new ArithmeticException("Divisor cannot be zero"); 7 8 return number1 / number2; 9 } public static void main(string[] args) { 12 Scanner input = new Scanner(System.in); // Prompt the user to enter two integers 15 System.out.print("Enter two integers: "); 16 int number1 = input.nextint(); 17 int number2 = input.nextint(); 18 We have defined the method thus we can handle the exception either in the main method or in the method itself 19 try { 20 int result = quotient(number1, number2); 21 System.out.println(number1 + " / " + number2 + " is " 22 + result); 23 } 24 catch (ArithmeticException ex) { 25 System.out.println("Exception: an integer " + 26 "cannot be divided by zero "); 27 } System.out.println("Execution continues..."); 30 } 31 } M. G. Abbas Malik, FCIT, UoJ 18

19 In case of library method, we cannot handle the exception in them We have to handle the exception in the calling method/code that we are writing/designing M. G. Abbas Malik, FCIT, UoJ 19

20 Input Miss Match Exception LISTING 12.5 InputMismatchExceptionDemo.java 1 import java.util.*; 2 3 public class InputMismatchExceptionDemo { 4 public static void main(string[] args) { 5 Scanner input = new Scanner(System.in); 6 boolean continueinput = true; 7 8 do { 9 try { 10 System.out.print("Enter an integer: "); 11 int number = input.nextint(); // Display the result 14 System.out.println("The number entered is " + number); continueinput = false; 17 } 18 catch (InputMismatchException ex) { 19 System.out.println("Try again. (" + "Incorrect input: an integer is required)"); 20 input.nextline(); // Discard input 21 } 22 } while (continueinput); 23 } 24 } M. G. Abbas Malik, FCIT, UoJ 20

21 Input Miss Match Exception LISTING 12.5 InputMismatchExceptionDemo.java 1 import java.util.*; 2 3 public class InputMismatchExceptionDemo { 4 public static void main(string[] args) { 5 Scanner input = new Scanner(System.in); 6 boolean continueinput = true; 7 8 do { 9 try { 10 System.out.print("Enter an integer: "); 11 int number = input.nextint(); // Display the result 14 System.out.println("The number entered is " + number); continueinput = false; This piece of code is not executed 17 } 18 catch (InputMismatchException ex) { 19 System.out.println("Try again. (" + "Incorrect input: an integer is required)"); 20 input.nextline(); // Discard input 21 } 22 } while (continueinput); 23 } 24 } M. G. Abbas Malik, FCIT, UoJ 21

22 Types of Exceptions Exceptions are objects, and objects are defined using classes The root class for exceptions is java.lang.throwable All Java exception classes inherit directly or indirectly from Throwable. You can create your own exception classes by extending Exception or a subclass of Exception. M. G. Abbas Malik, FCIT, UoJ 22

23 Types of Exceptions The class names Error, Exception, and RuntimeException are somewhat confusing. All three of these classes are exceptions, and all of the errors occur at runtime. M. G. Abbas Malik, FCIT, UoJ 23

24 Types of Exceptions Errors Exceptions are objects, and objects are defined using classes System errors are thrown by the JVM and are represented in the Error class. Error class describes internal system errors, though such errors rarely occur If one does, there is little you can do beyond notifying the user and trying to terminate the program gracefully M. G. Abbas Malik, FCIT, UoJ 24

25 Types of Exceptions Errors M. G. Abbas Malik, FCIT, UoJ 25

26 Types of Exceptions Exceptions Exceptions are represented in the Exception class, which describes errors caused by your program and by external circumstances These errors can be caught and handled by your program M. G. Abbas Malik, FCIT, UoJ 26

27 Types of Exceptions Exceptions M. G. Abbas Malik, FCIT, UoJ 27

28 Types of Exceptions Runtime Exceptions Runtime exceptions are represented in the RuntimeException class, which describes programming errors, such as bad casting, accessing an out-of-bounds array, and numeric errors. Runtime exceptions are generally thrown by the JVM M. G. Abbas Malik, FCIT, UoJ 28

29 Types of Exceptions Runtime Exceptions RuntimeException, Error, and their subclasses are known as Unchecked Exceptions All others are Checked Exceptions M. G. Abbas Malik, FCIT, UoJ 29

30 Types of Exceptions Checked Exceptions Compiler forces the programmer to check and deal with them in a try-catch block or declare it in the method header M. G. Abbas Malik, FCIT, UoJ 30

31 Types of Exceptions Unchecked Exceptions Unchecked exceptions reflect programming logic errors that are unrecoverable NullPointerException If we access an object through a reference variable before an object is assigned to it // Array variable is reference type variable int [] intarray; intarray[4] = 3; // throws a NullPointerException M. G. Abbas Malik, FCIT, UoJ 31

32 Types of Exceptions Unchecked Exceptions Unchecked exceptions reflect programming logic errors that are unrecoverable NullPointerException IndexOutOfBoundsException M. G. Abbas Malik, FCIT, UoJ 32

33 What RuntimeException will the following programs throw, if any? M. G. Abbas Malik, FCIT, UoJ 33

34 What RuntimeException will the following programs throw, if any? M. G. Abbas Malik, FCIT, UoJ 34

35 What RuntimeException will the following programs throw, if any? M. G. Abbas Malik, FCIT, UoJ 35

36 Multiple Catch Blocks to handle multiple exceptions try { Java Code to Run; A Statement or a method call that may throw an exception More Code to Run; } catch (ExceptionType1 identifier_variable) { Code to process the exception; } catch (ExceptionType2 identifier_variable) { Code to process the exception; } M. G. Abbas Malik, FCIT, UoJ 36

37 Multiple Catch Blocks to handle multiple exceptions M. G. Abbas Malik, FCIT, UoJ 37

38 Java s Exception Handling Model 1.Declaring an exception 2.Throwing an exception 3.Catching and exception M. G. Abbas Malik, FCIT, UoJ 38

39 M. G. Abbas Malik, FCIT, UoJ 39

40 Declaring an Exception Java requires that all checked exceptions thrown by a method must be declared explicitly in the method header M. G. Abbas Malik, FCIT, UoJ 40

41 Declaring an Exception Java requires that all checked exceptions thrown by a method must be declared explicitly in the method header M. G. Abbas Malik, FCIT, UoJ 41

42 Throwing an Exception M. G. Abbas Malik, FCIT, UoJ 42

43 Getting Information from Exception M. G. Abbas Malik, FCIT, UoJ 43

44 finally clause The code in the finally block is executed under all circumstances, regardless of whether an exception occurs in the try block or is caught. M. G. Abbas Malik, FCIT, UoJ 44

45 Re-throwing Exception M. G. Abbas Malik, FCIT, UoJ 45

46 Defining Custom Exception Class M. G. Abbas Malik, FCIT, UoJ 46

47 Advanced Programming Topics Covered Recursion Revisited Review of Object Oriented Concepts Exception Handling File and Stream Handling Binary I/O Multithreading and Parallel Programming Networking - Socket Programming Java Database Programming M. G. Abbas Malik, FCIT, UoJ 47