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![8 Without Exception Handling class WithoutExceptionHandling{ public static void main(String[] args){ int a,b; float r; a = 7; b = 0; r = a/b; System.out.println(“Result is “ + r); System.out.println(“Program reached this line”); } } Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam](https://image.slidesharecdn.com/java-exceptionhandlingconcepts-200510151131/75/Java-Exception-Handling-Concepts-8-2048.jpg)
![9 With Exception Handling class WithExceptionHandling{ public static void main(String[] args){ int a,b; float r; a = 7; b = 0; try{ r = a/b; System.out.println(“Result is “ + r); } catch(ArithmeticException e){ System.out.println(“ B is zero); } System.out.println(“Program reached this line”); } } Program Reaches here Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam](https://image.slidesharecdn.com/java-exceptionhandlingconcepts-200510151131/75/Java-Exception-Handling-Concepts-9-2048.jpg)
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Java - Exception Handling Concepts
The document discusses exception handling in Java. It explains that exceptions represent runtime errors and can be handled using try, catch, and finally blocks. The key exception types are Exception, RuntimeException, and Error. Exception is the superclass of all exceptions and must be caught, while RuntimeException represents programming errors that do not require catching. Error represents very severe errors outside the program's control. The document provides examples of how to throw, catch, and handle different exception types in Java code.
Java - Exception Handling Concepts
- 1. Exception Handling Dr. P.Victer Paul, Indian Institute of Information Technology Kottayam
- 2. 2 Why? Users mayuse our programs in an unexpected ways. Due to design errors or coding errors, programs may fail in unexpected ways during execution, or may result in an abnormal/abrupt program termination It is programmer’s responsibility to produce robust code that does not fail unexpectedly. Consequently, programmer must design error handling into our programs. Java – provides clear mechanism to Handle the Exceptions that happen during program execution. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 3. 3 What you know… In C, using the term “ERROR” is used to represent the unexpected interruption of code execution. Two types: Compile time Errors (Syntax and Semantic error) Runtime Errors (errors) Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 4. 4 Common Runtime Errors Dividing a number by zero. Accessing an element that is out of bounds of an array. Trying to store incompatible data elements. Using negative value as array size. Trying to convert from string data to a specific data value (e.g., converting string “abc” to integer value). File errors: Opening the file that does not exist opening a file in “read mode” that does not exist or no read permission Opening a file in “write/update mode” which has “read only” permission. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 5. 5 Exceptions Handling inJava An abnormal condition that arises in a code sequence at run time. In other words, an exception is a run-time error. A Java exception is an object that describes an exceptional (that is, error) condition that has occurred in a piece of code. When an exceptional condition arises, an object representing that exception is created and thrown in the method that caused the error. A program can deal with an exception object in one of three ways: ignore it handle it where it occurs handle it an another place in the programDr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 6. 6 Exceptions Handling inJava Java provides a robust and object oriented way to handle exception scenarios, known as Java Exception Handling. Java exception handling is managed via five keywords: try, catch, throw, throws, and finally. Program statements that you want to monitor for exceptions are contained within a try block. Catch block can handle it in some rational manner. System-generated exceptions are automatically thrown by the Java run-time system. To manually throw an exception, use the keyword throw. Any exception that is thrown out of a method must be specified as such by a throws clause. Any code that must be executed after a try block completes (with/without exception)is put in a finally block.Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 7. 7 Syntax of ExceptionHandling Code … … try { // statements } catch( Exception-Type e) { // statements to process exception } .. .. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 8. 8 Without Exception Handling classWithoutExceptionHandling{ public static void main(String[] args){ int a,b; float r; a = 7; b = 0; r = a/b; System.out.println(“Result is “ + r); System.out.println(“Program reached this line”); } } Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 9. 9 With Exception Handling classWithExceptionHandling{ public static void main(String[] args){ int a,b; float r; a = 7; b = 0; try{ r = a/b; System.out.println(“Result is “ + r); } catch(ArithmeticException e){ System.out.println(“ B is zero); } System.out.println(“Program reached this line”); } } Program Reaches here Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 10. 10 Exception Hierarchy Allexception types are subclasses of the built-in class Throwable. Throwable is at the top of the exception class hierarchy. Throwable are two subclasses partition exceptions into two distinct branches. Exceptions Errors Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 11. 11 Java Exception ClassHierarchy LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several more classes Several more classes Several more classes IllegalArgumentException Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 12. 12 Exception Class Exceptionis used for exceptional conditions that user programs should catch. This class is inherited to create subclass as programmer’s own custom exception types. There is an important subclass of Exception, called RuntimeException. Exceptions of this type are automatically defined for the programs that a programmer write. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 13. 13 Exception Class LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several moreclasses Several more classes Several more classes IllegalArgumentException Exception describes errors caused by your program and external circumstances. These errors can be caught and handled by your program. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 14. 14 Runtime Exceptions LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several moreclasses Several more classes Several more classes IllegalArgumentException RuntimeException is caused by programming errors, such as bad casting, accessing an out-of-bounds array, and numeric errors. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 15. 15 Error Exception TheError defines exceptions that are not expected to be caught under normal circumstances by your program. Exceptions of type Error are used by the Java run-time system to indicate errors having to do with the run-time environment, itself. Stack overflow is an example of such an error. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 16. 16 Error Exception Types LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Severalmore classes Several more classes Several more classes IllegalArgumentException System errors are thrown by JVM and represented in the Error class. The Error class describes internal system errors. Such errors rarely occur. If one does, there is little you can do beyond notifying the user and trying to terminate the program gracefully. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 17. 17 Error Exception Types Dr.P. Victer Paul, Indian Institute of Information Technology Kottayam
- 18. 18 Poll Question Considerthe JVM stops execution of a java program due to shortage of JVM memory. This scenario is A. Runtime Exception B. Error C. Checked Exception D. Exception Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 19. 19 Exception Types Exceptionsfall into two categories: Checked Exceptions Unchecked Exceptions Checked exceptions are inherited from the core Java class Exception. represent compile time exceptions that are coder responsibility to check. the compiler will issue an error message. RuntimeException, Error and their subclasses are known as unchecked exceptions. if not handled, your program will terminate with an appropriate error message. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 20. 20 Exception Types Dr. P.Victer Paul, Indian Institute of Information Technology Kottayam
- 21. 21 Exception Types LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several moreclasses Several more classes Several more classes IllegalArgumentException Unchecked exception. Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 22. 22 what happens whendon’t handle The call stack is quite useful for debugging, because it pinpoints the precise sequence of steps that led to the errorDr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 23. Predict the output 23Dr.P. Victer Paul, Indian Institute of Information Technology Kottayam
- 24. 24 Poll Question Output?? ACompile Error B Inside C Inside rest of the code D Inside Null rest of the code Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 25. Handling Exception Differentmechanism. Simple try - catch try with multiple catch multiple exception with single catch nested try statements throw Throws try, catch and finally (exception with exit code) Java Exception Propagation 25Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 26. Simple try -catch The try block allows you to define a block of code to be tested/monitor for errors while it is being executed. The catch block allows you to define a block of code to be executed, if an error occurs in the try block. 26Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 27. Example 27Dr. P. VicterPaul, Indian Institute of Information Technology Kottayam
- 28. Try with multiplecatch In some cases, more than one exception could be raised by a single piece of code. To handle this type of situation, you can specify two or more catch clauses, each catching a different type of exception. When an exception is thrown, each catch statement is inspected in order, and the first one whose type matches that of the exception is executed. After one catch statement executes, the others are bypassed 28Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 29. Try with multiplecatch Ex 29Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 30. multiple exception withsingle catch When you use multiple catch statements, it is important to remember that exception subclasses must come before any of their superclasses. This is because a catch statement that uses a superclass will catch exceptions of that type plus any of its subclasses. Thus, a subclass would never be reached if it came after its superclass. Further, in Java, unreachable code is an error. 30Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 31. multiple exception withsingle catch Ex 31Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 32. multiple exception withsingle catch Ex 32Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 33. nested try statements The try statement can be nested. That is, a try statement can be inside the block of another try. If an inner try statement does not have a catch handler for a particular exception, the stack is unwound and the next try statement’s catch handlers are inspected for a match. This continues until one of the catch statements succeeds, or until all of the nested try statements are exhausted. If no catch statement matches, then the Java run-time system will handle the exception 33Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 34. nested try statementsEx 34Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 35. 35 Poll Question Whichof these is a super class of all errors and exceptions in the Java language? A RunTimeExceptions B Throwable C Catchable D None of the above Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 36. Handling Exception Differentmechanism. Simple try - catch try with multiple catch multiple exception with single catch nested try statements throw Throws try, catch and finally (exception with exit code) Java Exception Propagation 36Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 37. throw So far,you have only been catching exceptions that are thrown by the Java run-time system. However, it is possible for your program to throw an exception explicitly, using the throw statement. Syntax: Here, ThrowableInstance must be an object of type Throwable or a subclass of Throwable. The flow of execution stops immediately after the throw statement; any subsequent statements are not executed. If no matching catch is found, then the default exception handler halts the program and prints the stack trace 37Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 38. throw 38Dr. P. VicterPaul, Indian Institute of Information Technology Kottayam
- 39. Throws If amethod is capable of causing an exception that it does not handle, it must specify this behavior so that callers of the method can guard themselves against that exception. You do this by including a throws clause in the method’s declaration. A throws clause lists the types of exceptions that a method might throw. This is necessary for all exceptions, except those of type Error or RuntimeException, or any of their subclasses. If they are not, a compile-time error will result. 39Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 40. Throws This isthe general form of a method declaration that includes a throws clause: exception-list is a comma-separated list of the exceptions that a method can throw. First, you need to declare that throwOne( ) throws IllegalAccessException. Second, main( ) must define a try/catch statement that catches this exception. 40Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 41. Throws 41Dr. P. VicterPaul, Indian Institute of Information Technology Kottayam
- 42. Throws 42Dr. P. VicterPaul, Indian Institute of Information Technology Kottayam
- 43. try, catch andfinally When exceptions are thrown, execution in a method takes a rather abrupt, nonlinear path that alters the normal flow through the method. This could be a problem in some methods. For example, if a method opens a file upon entry and closes it upon exit, then you will not want the code that closes the file to be bypassed by the exception-handling mechanism. The finally keyword is designed to address this contingency 43Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 44. try, catch andfinally finally creates a block of code that will be executed after a try/catch block has completed and before the code following the try/catch block. The finally block will execute whether or not an exception is thrown. 44Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 45. try, catch andfinally 45Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 46. Java’s Built-in Exceptions Inside the standard package java.lang, Java defines several exception classes. A few have been used by the preceding examples. 46Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 47. Java’s Built-in Exceptions 47Dr.P. Victer Paul, Indian Institute of Information Technology Kottayam
- 48. Java’s Built-in Exceptions 48Dr.P. Victer Paul, Indian Institute of Information Technology Kottayam
- 49. Creating Your ExceptionSubclasses Although Java’s built-in exceptions handle most common errors user probably want to create your own exception types to handle situations specific to your applications. This is quite easy to do: just define a subclass of Exception (which is, of course, a subclass of Throwable). class UserException extends Exception { } 49Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 50. Creating Your ExceptionSubclasses class InvalidMobile extends Exception { InvalidMobile(String msg) { super(msg); } } 50Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 51. Creating Your ExceptionSubclasses 51Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 52. Creating Your ExceptionSubclasses 52Dr. P. Victer Paul, Indian Institute of Information Technology Kottayam
- 53. 53 The End… Dr. P.Victer Paul, Indian Institute of Information Technology Kottayam