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PPL: Exceptions

EXCEPTIONS

Viva Voce on Exceptions

Q1. What is the difference between error and exception in java?
Errors are mainly caused by the environment in which an application is running. For example, OutOfMemoryError happens when JVM runs out of memory. 
Exceptions are mainly caused by the application itself. For example, NullPointerException occurs when an application tries to access null object.

Q2. Can we write only try block without catch and finally blocks?
No, It shows compilation error. The try block must be followed by either catch or finally block. You can remove either catch block or finally block but not both.

Q3. What are run time exceptions in java. Give example?
The exceptions which occur at run time. These exceptions are unknown to compiler. All sub classes of java.lang.RunTimeException and java.lang.Error are run time exceptions. These exceptions are unchecked type of exceptions. For example, 
  • NumberFormatException, 
  • NullPointerException, 
  • ClassCastException, 
  • ArrayIndexOutOfBoundException, 
  • StackOverflowError etc.
Q4. What is OutOfMemoryError in java?
OutOfMemoryError is the sub class of java.lang.Error which occurs when JVM runs out of memory.

Q5. Can we keep the statements after finally block If the control is returning from the finally block itself?
No, it gives unreachable code error. Because, control is returning from the finally block itself. Compiler will not see the statements after it. That’s why it shows unreachable code error

Q6. Does finally block get executed If either try or catch blocks are returning the control?
Yes.

Q7. What is Re-throwing an exception in java?
Exceptions raised in the try block are handled in the catch block. If it is unable to handle that exception, it can re-throw that exception using throw keyword. It is called re-throwing an exception.

Q8. What is ClassCastException in java?
ClassCastException is a RunTimeException which occurs when JVM unable to cast an object of one type to another type.

Q9. Which class is the super class for all types of errors and exceptions in java?
java.lang.Throwable is the super class for all types of errors and exceptions in java.

Q10. What is the use of printStackTrace() method?
printStackTrace() method is used to print the detailed information about the exception occurred.

Q11. Give some examples to checked exceptions?
ClassNotFoundException, SQLException, IOException.

Q12. Give some examples to unchecked exceptions?
NullPointerException, ArrayIndexOutOfBoundsException, NumberFormatException.

Q13. What Is the Difference Between Throw and Throws Keywords in Java?
The throws keyword is used with a method signature to declare exceptions that the method might throw, whereas the throw keyword is used to disrupt the flow of a program and handing over the exception object to run-time to handle it.

Q14. What Happens When an Exception Is Thrown by the Main Method?
When an exception is thrown by mainmethod(), Java Runtime terminates the program and prints the exception message and the stack trace in-system console.

Q15. What Is a Stacktrace and How Does it Relate to an Exception?
A stack trace provides the names of the classes and methods that were called, from the start of the application to the point that an exception occurred. It’s a very useful debugging tool since it enables us to determine exactly where the exception was thrown in the application and the original causes that led to it.

Q16. What is the difference between a checked and an unchecked exception?
A checked exception must be handled within a try-catch block or declared in a throws clause; whereas an unchecked exception is not required to be handled nor declared. Checked and unchecked exceptions are also known as compile-time and runtime exceptions respectively. All exceptions are checked exceptions, except those indicated by Error, RuntimeException, and their subclasses.


MCQs on Exceptions

Q1. When does Exceptions in Java arises in code sequence?
● A. Run Time
● B. Compilation Time
● C. Can Occur Any Time

Q2. Which of these keywords is not a part of exception handling?
● A. try
● B. finally
● C. thrown

Q3. Which of these keywords must be used to monitor for exceptions?
● A. try
● B. finally
● C. throw

Q4. Which of these keywords is used to manually throw an exception?
● A. try
● B. finally
● C. throw

Q5. Which of these is a super class of all exceptional type classes?
● A. String
● B. RuntimeExceptions
● C. Throwable

Q6. Which of these class is related to all the exceptions that cannot be caught?
● A. Error
● B. Exception
● C. RuntimeExecption

Q7. Which of these handles the exception when no catch is used?
● A. Default handler
● B. finally
● C. throw handler


MCQs Answers

Q1. (A)
Q2. (C)
Q3. (A)
Q4. (C)
Q5. (C)
Q6. (B)
Q7. (C) 

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