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Technical General Java Sample Questions

  1. What are checked exceptions?

    Answer: Checked exception are those which the Java compiler forces you to catch.e.g.IOException are checked Exceptions.

  2. What are runtime exceptions?

    Answer: Runtime exceptions are those exceptions that are thrown at runtime because of either wrong input data or because of wrong business logic etc.These are not checked by the compiler at compile time.

  3. What is the difference between error and an exception?

    Answer: An error is an irrecoverable condition occurring at runtime.Such as OutOfMemory error.These JVM errors and you can not repair them at runtime.While exceptions are conditions that occur because of bad input etc.e.g.FileNotFoundException will be thrown if the specified file does not exist.Or a NullPointerException will take place if you try using a null reference.In most of the cases it is possible to recover from an exception (probably by giving user a feedback for entering proper values etc.).

  4. How to create custom exceptions?

    Answer: Your class should extend class Exception, or some more specific type thereof.

  5. If I want an object of my class to be thrown as an exception object, what should I do?

    Answer: The class should extend from Exception class.Or you can extend your class from some more precise exception type also.

  6. If my class already extends from some other class what should I do if I want an instance of my class to be thrown as an exception object?

    Answer: One can not do anytihng in this scenarion.Because Java does not allow multiple inheritance and does not provide any exception interface as well.

  7. What happens to an unhandled exception?

    Answer: One can not do anytihng in this scenarion.Because Java does not allow multiple inheritance and does not provide any exception interface as well.

  8. How does an exception permeate through the code?

    Answer: An unhandled exception moves up the method stack in search of a matching When an exception is thrown from a code which is wrapped in a try block followed by one or more catch blocks, a search is made for matching catch block.If a matching type is found then that block will be invoked.If a matching type is not found then the exception moves up the method stack and reaches the caller method.Same procedure is repeated if the caller method is included in a try catch block.This process continues until a catch block handling the appropriate type of exception is found.If it does not find such a block then finally the program terminates.

  9. What are the different ways to handle exceptions?

    Answer: There are two ways to handle exceptions, 1.By wrapping the desired code in a try block followed by a catch block to catch the exceptions.and 2.List the desired exceptions in the throws clause of the method and let the caller of the method hadle those exceptions.

  10. What is the basic difference between the 2 approaches to exception handling...
    • try catch block and
    • specifying the candidate exceptions in the throws clause?When should you use which approach?

    Answer: In the first approach as a programmer of the method, you urself are dealing with the exception.This is fine if you are in a best position to decide should be done in case of an exception.Whereas if it is not the responsibility of the method to deal with it's own exceptions, then do not use this approach.In this case use the second approach.In the second approach we are forcing the caller of the method to catch the exceptions, that the method is likely to throw.This is often the approach library creators use.They list the exception in the throws clause and we must catch them.You will find the same approach throughout the java libraries we use.

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