Java Interview Questions

 

What is an Exception?

An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions.

Explain the user defined Exceptions?

User defined Exceptions are the separate Exception classes defined by the user for specific purposed. An user defined can created by simply sub-classing it to the Exception class. This allows custom exceptions to be generated (using throw) and caught in the same way as normal exceptions.
Example:

class myCustomException extends Exception {
     / The class simply has to exist to be an exception
}

Where does Exception stand in the Java tree hierarchy?

What are checked and unchecked exceptions?

Checked exceptions are the ones which you expect beforehand to be raised when an exceptional condition occurs and so write your code in a try-catch block to handle that sufficiently. For example: InsuffucientBalanceException which might be raised when money is being withdrawn from a bank account and the account has insufficient balance. Checked exceptions are sub classes of Exception.

Unchecked exceptions are the ones which cannot be handled in the code. These are rather unexpected exceptions like NullPointerException, OutOfMemoryError, DivideByZeroException, typically, programming errors. Unchecked exceptions are subclasses of RunTimeExceptions.

 

Is it compulsory to use the finally block?

No, you can use it if you need to do something if exception occours or not final block will always execute. If you need like database connection closeing or file closeing then you can use this block.

How are try, catch and finally block organized?

try {
statements;
} catch (exceptionType1 identifier1) {
// one or multiple statements;
} catch (exceptionType2 identifier2) {
statements;
}
...
}
finally {
// one or none statements;
}

 

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