Programming in java by balagurusamy, Lecture notes of Java Programming

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Unit IV

Exception

Handling

Illustration of Compile-Time Errors

Class Error { Public static void main(String args[]) { System.out.println(“Hello Java”) //Missing; } }

Error1.java :7: ‘;’ expected

System.out.println (“Hello Jaav”)

^

1 error

Error1.java :7: ‘;’ expected

System.out.println (“Hello Jaav”)

^

1 error

The Most Common Compile Time Errors are

• (^) Missing Semicolons
• (^) Missing (or mismatch of) brackets in classes and methods
• (^) Misspelling of identifiers and keywords
• (^) Missing double quotes in strings
• (^) Use of undeclared variables
• (^) Incompatible types in assignments/initialization
• (^) Bad references to objects
• (^) Use of = in place of == operator
• (^) And so on

The Most Common Compile Time Errors are

• (^) Dividing an integer by zero
• (^) Accessing an element that is not of the bounds of an array
• (^) Trying to store a value into an array of an incompatible class or type
• (^) Trying to cast an instance of a class to one of its subclasses
• (^) Passing a parameter that is not in a valid range or value for a method
• (^) Trying to illegally changes the state of a thread
• (^) Attempting to use a negative size for an array
• (^) Using a null object reference as a legitimate object reference to access a method or a variable
• (^) Converting invalid string to a number
• (^) Accessing a character that is out of bounds of a string

Exception

• (^) An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program's instructions. Exception = Exceptional Event

Error Handling code that performs the

following tasks

• (^) Find the problem ( Hit the exception )
• (^) Inform that an error has occurred ( Throw the exception )
• (^) Receive the error information ( Catch the exception )
• (^) Task corrective actions ( Handle the exception )

Exception Classes

LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several more classes Several more classes Several more classes IllegalArgumentException

Exceptions

LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several more classes 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

LinkageError Error AWTError AWTException Throwable ClassNotFoundException VirtualMachineError IOException Exception RuntimeException Object ArithmeticException NullPointerException IndexOutOfBoundsException Several more classes Several more classes Several more classes IllegalArgumentException

Runtime Exceptions

Runtime Exception^ Runtime Exception

Syntax of Exception Handling Code

Exception object creator

Exception Handler

Try Block

Statement that causes an exception

Catch Block

Statement that handles the exception

Throws exception object

Example

Class Error { Public static void main(String args[]) { Int a=10; Int b=5; Int c=5; Int x,y; try { x=a/(b-c); } catch (ArithmeticException e) { System.out.println(“Division by Zero”); } Y=a/(b+c); System.out.println(“y=“+y); } }

Output

Division by Zero

Y= 1

Output

Division by Zero

Y= 1

Example

Class Error

Public static void main(String args[])

Int a[]={5,10};

Try

Int x=a[2]/b-a[1];

Catch(ArithmeticException e)

System.out.println(“Division by Zero”);

Catch(ArrayindexOutOfBoundsException e)

System.out.println(“Array Index Error”);

Catch(ArrayStoreException e)

System.out.println(“Wrong data type”);

Int y=a[1]/a[0];

System.out.println(“y=“+y);

Output1:

Array Index Error

Y=

Output1:

Array Index Error

Y=

Using finally Statement

Syntax