Exception Handling in Java

BY
K.LALITHAMBIGA
II –Msc (CS&IT )
Department of CS&IT
NS College of Arts and Science,
Theni.

Exception Handling
 Exception are run time anomalies or unusual condition that a program may
encounter during execution.
Type of Program errors
We distinguish between the following types of errors:
• Syntax error: Errors due to the fact that the syntax of the language
is not respected.
• Semantic error: Errors due to an improper use of program
statements.
• Logical errors: Errors due to the fact that the specification is not
respected.
From the point of view of when errors are detected
 Compile time error: Syntax errors & Static semantic errors indicated
by the compiler.
 Runtime errors: Dynamic semantic errors, that errors, that cannot be
detected by the compiler(debugging).

Exception Handling
Runtime Errors
 Division by zero
 Access to an array outside of its bounds
 Running out of memory
 Running out of disk space
 It was not a part of original C++
 It is a new feature added to ANSI C++
Exception are Two kinds:
 Synchronous Exception
 Out of rage
 Over flow
 Asynchronous Exception
 Error that are caused by causes beyond the control of the program.
 Keyboard interrupts.
In C++ only Synchronous exception can be handled.

Exception Handling
Exception Handling Mechanism
 Find the problem (Hit the Exception)
 Inform that an error has occurred (Throw the Exception)
 Receive the error information (Catch the Exception)
 Take corrective action (Handle the Exception)
Exception in Java can be categorized into two types:
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
UnChecked Exception:
 These Exception are not essentially handled in the program code; instead
the JVM handles such exceptions.
 Unchecked Exceptions are extended from the
java.lang.RuntimeException class

 It is basically build upon three keywords.
 Try
 Throw
 Catch
Throws
Exception
Object
Catch Block
Catch & handle the Exception
Try Block
Detects & throws and Exception

 The Keyword Try is used to preface a block of statements which
may generate exceptions.
 When an exception is detected, it is Thrown using a throw
statement in the try block.
 A Catch block defined by the Keyword ‘catch’ catches the
exception and handles it appropriately.
 The catch block that catches an exception must immediately
follow the try block that throws the exception.

try
{
… //Block of statements
throw exception; //which detect and
… //throws an exception
}
catch(type arg) //catch exception
{
… //Block of statement
… //that handles the exception
}

Exception are objects used to transmit information about a
problem.
If the type of the object thrown matches the arg type in the
catch statement, the catch block is executed.
If they do not match, the program is aborted using the abort()
function (default).
Exception are thrown by functions that are invoked from within
the try blocks.
The point at which the throw is executed is called throw point.
Once an exception is thrown to the catch block, control cannot
return to the thrown point

Throw Point
•Function that cause
an Exception
Catch Block
•Catch & handle the
Exception
Try Block
•Invokes a function that
contains an Exception
Throws Exception
Invoke function

Throwing Mechanism
 The throw statement can have one of the following 3 forms
 Throw(exception)
 Throw exception
 Throw //used to re-throw a exception
• The operand object exception can be of any type, including
constant.
• It is also possible to throw an object not intended for error
handling.
• Throw point can be in a deeply nested scope within a try
block or in a deeply nested function call.
• In any case, control is transferred to the catch statement.
Throw new Throwable subclass;

Catching Mechanism
 The type indicates the type of exception the catch block handles.
 The parameter arg is an optional parameter name.
 The catch statement catches an exception whose type matches with
the type of the catch argument.
 If the parameter in the catch statement is name, then the parameter
can be used in the exception handling code.
 If a catch statement does not match the exception it is skipped.
 More than one catch statement can be associated with a try block.
Catch(type arg)
{
….
….
….
}

Catching Mechanism
Multiple catch statement
Try {
statement; //generates an exception
}
Catch(type 1 arg) {
statement; //catch block 1
}
Catch(type 2 arg){
statement; //catch block 2
}
…
...
Catch(type N arg) {
statement; //catch block N
}

Catching Mechanism
 When an exception is thrown, the exception handlers are
searched in order for a match.
 The first handler that yields a match is executed.
 If several catch statement matches the type of an
exception the first handler that matches the exception type
is executed.
 Catch all exception
Catch(….)
{
//statement for processing all exception
}

Using Finally statement
Try {
Try-block }
Catch(Exception class 1 e) {
catch-block }
Catch(Exception class 2 e) {
catch-block }
…
Finally{
Finally-block }

Using Finally statement
 Try-block: sequence of statements that will be executed
under the control of the following catch clauses.
 Catch-block: Sequence of statements that will be executed
if a statement in the try-block generates an exception of
the type specified in the corresponding catch clause.
 Finally-block: Sequence of statements that will be always
executed (both in the case where the try-block is executed
without exceptions, and in the case where a catch-block is
executed to catch an exception).

Common Java Exception
Exception Cause of Exception
Arithmetic Exception Math errors such as division by zero
ArrayIndexOutofBoundsException Bad array indexes
ArrayStoreException When a program tries to store the wrong type of data in
an array
FileNotFoundException Attempt to access a non existent file
IOException General I/O failures, such as inability to read from a file
NullPointerException Referencing a null object
NumberFormatException When a conversion between strings & number fails
OutOfMemoryException When there’s not enough memory to allocate a new
object
SecurityException When an applet tries to perform an action not allowed by
the browser’s security setting
StackOverFlowException When the system runs out of stack space
StringIndexOutOfBoundException When a program attempts to access a nonexistent
character position in a string

Exception Handling in Java

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