EXCEPTION HANDLING

Error:

    Errors are the mistakes that make the program go wrong.

     An error may produce an incorrect output or may terminate the execution of the program abruptly or even may cause the system to crash.

    Errors are classified into two categories:

o   Compile Time Errors: All errors will be detected and displayed by the Java compiler and therefore these errors are known as compile-time errors. Whenever a compiler displays an error, it will not create the .class file.

The common compile time errors are:

§  Missing semicolons.

§  Missing (or mismatch of) brackets in classes and methods.

§  Misspelling of identifiers and keywords.

§  Use of undeclared variables and many more.

o   Run Time Errors:Sometimes a program may compile properly and producing .class files but May not run properly. Most common run-time errors are:

§  Divide an Integer by zero.

§  Accessing an element that is out of the bounds of an array.

§  Converting invalid string to a number.

§  Attempting to use a negative size for an array and many more.

Exception Types:

    An Exception is a condition that is caused by a run-time error in the program.

    Exceptions in Java can be categorized into two types:

o   Checked Exception: These exceptions are explicitly handled in the code itself with the help of try catch blocks. Checked exceptions are extended from the java.lang.Exceptionclass.

o   Unchecked Exceptions:These exceptions are not essentially handled in the code; instead the JVM handles such exceptions. Unchecked exceptions are extended from the java.lang.RuntimeExceptionclass.

    Some common Java Exceptions are:

Exception Type	Cause of Exception
ArithmeticException	Caused by math errors such as division by zero.
ArrayIndexOutOfBoundsException	Caused by bad array indexes.
ArrayStoreException	Caused when a program tries to store the wrong type of data in an array.
FileNotFoundException	Caused by an attempt to access a nonexistent file.
IOException	Caused by general I/O failures, such as inability to read from a file.
NullPointerException	Caused by referencing a null object.
NumberFormatException	Caused when the conversion between strings and numbers fails.
OutOfMemoryException	Caused when there’s not enough memory to allocate a new object.
SecurityException	Caused when an applet tries to perform an action not allowed by the browser’s security setting.
StackOverFlowException	Caused when the system runs out of stack space.
StringIndexOutOfBoundsException	Caused when a program attempts to access a nonexistent character position in a string.

    Exception Handling:The purpose of exception handling mechanism is to provide a means to detect and report an “exceptional circumstance” so that appropriate action can be taken. The following tasks must be performed during exception handling:

o   Find the problem(Hit the exception)

o   Inform that an error has occurred(Throw the exception)

o   Receive the error information(Catch the exception)

o   Take corrective action(Handle the exception)