Q) Diff Exception & Error
Exception
and Error both are subclasses of the Throwable class.
ExceptionàException is
generated by java runtime system (or) by manually. An exception is a abnormal
condition that transfer program execution from a thrower to catcher.
Error
àWill
stop the program execution, Error is a abnormal system condition we cannot
handle these.
Q)
Can an exception be rethrown?
A) Yes, an exception can be rethrown.
Q)
try, catch, throw, throws
try à This is used to fix
up the error, to prevent the program from automatically terminating, try-catch
is used to catching an exception that are thrown by the java runtime system.
Throw à is used to throw an
exception explicitly.
Throws à A Throws clause list the type of exceptions
that a methods might through.
Q) What happens if
an exception is not caught?
A) An uncaught exception results in the uncaughtException()
method of the thread's ThreadGroup being invoked, which eventually results in
the termination of the program in which it is thrown.
Q) What happens if
a try-catch-finally statement does not have a catch clause to handle an
exception that is thrown within the body of the try statement?
The exception propagates up to the next
higher level try-catch statement (if any) or results in the program's
termination.
Q) Checked & UnChecked
Exception :-
Checked exception is some subclass of
Exception. Making an exception checked forces client programmers to deal with
the possibility that the exception will be thrown. eg, IOException thrown by
java.io.FileInputStream's read() method·
Unchecked exceptions are RuntimeException and
any of its subclasses. Class Error and its subclasses also are unchecked. With
an unchecked exception, however, the compiler doesn't force client programmers
either to catch the exception or declare it in a throws clause. In fact, client
programmers may not even know that the exception could be thrown. eg,
StringIndexOutOfBoundsException thrown by String's charAt() method· Checked
exceptions must be caught at compile time. Runtime exceptions do not need to
be. Errors often cannot be.
|
Checked Exceptions
|
Un checked exception
|
ClassNotFoundException
|
ArithmeticException
|
NoSuchMethodException |
ArrayIndexOutOfBoundException
|
|
NoSuchFieldException
|
ClasscastException
|
|
InterruptedException
|
IllegalArgumentException
|
IllegalAccessException
|
IllegalMonitorSateException
|
CloneNotSupportedException
|
IllegalThreadStateException
|
|
|
IndexOutOfBoundException
|
|
|
NullPointerException
|
|
|
NumberFormatException
|
|
|
StringIndexOutOfBounds
|
OutOfMemoryError --> Signals that JVM has
run out of memory and that the garbage collector is unable to claim any more
free memory.
StackOverFlow --> Signals that a stack O.F in the interpreter.
ArrayIndexOutOfbound --> For accessing an array element by providing an index values <0 or="or"> or equal to the array size.
StringIndexOutOfbound --> For accessing character of a string or string buffer with index values
<0 or="or"> or equal to the array size.
Arithmetic Exception --> such as divide by zero.
ArrayStore Exception --> Assignment to an array element of an incompatible types.
ClasscastException --> Invalid casting.
IllegalArgument Exception --> Illegal argument is used to invoke a method.
Nullpointer Exception --> If attempt to made to use a null object.
NumberFormat Exception --> Invalid conversition of string to numeric format.
ClassNotfound Exception --> class not found.
Instantion Exception --> Attempt to create an object of an Abstract class or Interface.
NosuchField Exception --> A request field does not exist.
NosuchMethod Exception --> A request method does not exist.
Q) Methods in Exceptions?
A) getMessage(),
toString(), printStackTrace(), getLocalizedMessage(),
Q) What is exception chaining?
A) An exception chain is a list of all the
exceptions generated in response to a single root exception. As
each exception is caught and converted to a higher-level
exception for rethrowing, it's added to the chain.
This provides a complete record of how an exception is
handled The chained exception API was introduced in 1.4. Two methods and two
constructors were added to Throwable.
Throwable getCause()
Throwable initCause(Throwable)
Throwable(String, Throwable)
Throwable(Throwable)
The Throwable argument to initCause and the
Throwable constructors is the exception that caused the current exception.
getCause returns the exception that caused the current exception, and initCause
returns the current exception.
Q) Primitive multi tasking
If the threads of different
priorities shifting the control depend on the priority i.e.; a thread with
higher priority is executed first than the thread with lower priority. This
process of shifting control is known as primitive multi tasking.
Q) Http Status Codes
To
inform the client of a problem at the server end, you call the “sendError”
method. This causes the server to respond with status line, with protocol
version and a success or error code.
The first digit of the status code defines
the class of response, while the last two digits do not have categories
Number |
Type |
Description |
1xx
|
Informational
|
Requested received, continuing to process
|
2xx
|
Success
|
The action was successfully received, understood, and accepted
|
3xx
|
Redirection
|
Further action must be taken in order to complete the request
|
4xx
|
Client Error
|
The request contains bad syntax or cannot be fulfilled
|
5xx
|
Server Error
|
The server failed to fulfil valid request
|
