Difference between java lang RuntimeException and java lang Exception

Question

Someone please explain the difference between java lang RuntimeException and java lang Exception   How do I decide which one to extend if I create my own exception

User · Answer

Before looking at the difference between java.lang.RuntimeException and java.lang.Exception classes, you must know the Exception hierarchy. Both Exception and Error classes are derived from class Throwable (which derives from the class Object). And the class RuntimeException is derived from class Exception.

All the exceptions are derived either from Exception or RuntimeException.

All the exceptions which derive from RuntimeException are referred to as unchecked exceptions. And all the other exceptions are checked exceptions. A checked exception must be caught somewhere in your code, otherwise, it will not compile. That is why they are called checked exceptions. On the other hand, with unchecked exceptions, the calling method is under no obligation to handle or declare it.

Therefore all the exceptions which compiler forces you to handle are directly derived from java.lang.Exception and all the other which compiler does not force you to handle are derived from java.lang.RuntimeException.

Following are some of the direct known subclasses of RuntimeException.

AnnotationTypeMismatchException,
ArithmeticException,
ArrayStoreException,
BufferOverflowException,
BufferUnderflowException,
CannotRedoException,
CannotUndoException,
ClassCastException,
CMMException,
ConcurrentModificationException,
DataBindingException,
DOMException,
EmptyStackException,
EnumConstantNotPresentException,
EventException,
IllegalArgumentException,
IllegalMonitorStateException,
IllegalPathStateException,
IllegalStateException,
ImagingOpException,
IncompleteAnnotationException,
IndexOutOfBoundsException,
JMRuntimeException,
LSException,
MalformedParameterizedTypeException,
MirroredTypeException,
MirroredTypesException,
MissingResourceException,
NegativeArraySizeException,
NoSuchElementException,
NoSuchMechanismException,
NullPointerException,
ProfileDataException,
ProviderException,
RasterFormatException,
RejectedExecutionException,
SecurityException,
SystemException,
TypeConstraintException,
TypeNotPresentException,
UndeclaredThrowableException,
UnknownAnnotationValueException,
UnknownElementException,
UnknownTypeException,
UnmodifiableSetException,
UnsupportedOperationException,
WebServiceException

User · Answer

An Exception is checked  and a RuntimeException is unchecked   Checked means that the compiler requires that you handle the exception in a catch  or declare your method as throwing it  or one of its superclasses    Generally  throw a checked exception if the caller of the API is expected to handle the exception  and an unchecked exception if it is something the caller would not normally be able to handle  such as an error with one of the parameters  i e  a programming mistake

User · Answer

The runtime exception classes  RuntimeException and its subclasses  are exempted from compile-time checking  since the compiler cannot establish that run-time exceptions cannot occur   from JLS    In the classes that you design you should subclass Exception and throw instances of it to signal any exceptional scenarios  Doing so you will be explicitly signaling the  clients of your class that usage of your class might throw exception and they have to  take steps to handle those exceptional scenarios    Below code snippets explain this point       Create your own exception class subclassing from Exception class MyException extends Exception       public MyException final String message            super message            public class Process       public void execute             throw new RuntimeException  Runtime                public void process   throws MyException           throw new MyException  Checked              In the above class definition of class Process  the method execute can  throw a RuntimeException but the method declaration need not specify that  it throws RuntimeException   The method process throws a checked exception and it should declare that it will throw a checked exception of kind MyException and not doing so will be  a compile error   The above class definition will affect the code that uses Process class as well   The call new Process   execute   is a valid invocation where as the call of form new Process   process   gives a compile error  This is because the client code should take steps to handle MyException  say call to process   can be enclosed in  a try catch block

User · Answer

Proper use of RuntimeException   From Unchecked Exceptions -- The Controversy      If a client can reasonably be expected   to recover from an exception  make it   a checked exception  If a client   cannot do anything to recover from the   exception  make it an unchecked   exception    Note that an unchecked exception is one derived from RuntimeException and a checked exception is one derived from Exception   Why throw a RuntimeException if a client cannot do anything to recover from the exception   The article explains      Runtime exceptions represent problems   that are the result of a programming   problem  and as such  the API client   code cannot reasonably be expected to   recover from them or to handle them in   any way  Such problems include   arithmetic exceptions  such as   dividing by zero  pointer exceptions    such as trying to access an object   through a null reference  and indexing   exceptions  such as attempting to   access an array element through an   index that is too large or too small

User · Answer

In Java  there are two types of exceptions   checked exceptions and un-checked exceptions   A checked exception must be handled explicitly by the code  whereas  an un-checked exception does not need to be explicitly handled   For checked exceptions  you either have to put a try catch block around the code that could potentially throw the exception  or add a  throws  clause to the method  to indicate that the method might throw this type of exception  which must be handled in the calling class or above    Any exception that derives from  Exception  is a checked exception  whereas a class that derives from RuntimeException is un-checked   RuntimeExceptions do not need to be explicitly handled by the calling code

User · Answer

From oracle documentation      Here s the bottom line guideline  If a client can reasonably be   expected to recover from an exception  make it a checked exception  If   a client cannot do anything to recover from the exception  make it an   unchecked exception    Runtime exceptions represent problems that are the result of a programming problem and as such  the API client code cannot reasonably be expected to recover from them or to handle them in any way   RuntimeExceptions are like  exceptions by invalid use of an api  examples of runtimeexceptions  IllegalStateException   NegativeArraySizeException  NullpointerException   With the Exceptions you must catch it explicitly because you can still do something to recover  Examples of Exceptions are  IOException  TimeoutException  PrintException

User · Answer

In simple words  if your client user can recover from the Exception then make it a Checked Exception  if your client can t do anything to recover from the Exception then make it Unchecked RuntimeException  E g  a RuntimeException would be a programmatic error  like division by zero  no user can do anything about it but the programmer himself  then it is a RuntimeException

User · Answer

RuntimeException is a child class of Exception class  This is one of the many child classes of Exception class  RuntimeException is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine  A method is not required to declare in its throws clause any subclasses of RuntimeException that might be thrown during the execution of the method but not caught   The hierchy is  java lang Object  ---java lang Throwable  -------java lang Exception  -------------java lang RuntimeException

User · Answer

Exceptions are a good way to handle unexpected events in your application flow  RuntimeException are unchecked by the Compiler but you may prefer to use Exceptions that extend Exception Class to control the behaviour of your api clients as they are required to catch errors for them to compile  Also forms good documentation    If want to achieve clean interface use inheritance to subclass the different types of exception your application has and then expose the parent exception

User · Answer

User-defined Exception can be Checked Exception or Unchecked Exception  It depends on the class it is extending to  User-defined Exception can be Custom Checked Exception  if it is extending to Exception class User-defined Exception can be Custom Unchecked Exception   if it is extending to Run time Exception class  Define a class and make it a child to Exception or Run time Exception

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There are two types of exception  You can recover from checked exception if you get such kind of exception  Runtime exception are irrecoverable  runtime exceptions are programming errors  and programmer should take care of it while writing the code  and continue execution of this might give you incorrect result  Runtime exceptions are about violating precondition ex  you have an array of size 10  and you are trying to access 11 th element  it will throw ArrayIndexOutOfBoundException

User · Answer

Generally RuntimeExceptions are exceptions that can be prevented programmatically  E g  NullPointerException  ArrayIndexOutOfBoundException  If you check for null before calling any method  NullPointerException would never occur  Similarly ArrayIndexOutOfBoundException would never occur if you check the index first  RuntimeException are not checked by the compiler  so it is clean code   EDIT   These days people favor RuntimeException because the clean code it produces  It is totally a personal choice

[java] Difference between java.lang.RuntimeException and java.lang.Exception

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