CHp 9 - ExceptionHandling

Question 1

What is an exception?

Answer 1

Event during execution disrupting normal flow; it is thrown.

Question 2

Who must detect and handle exceptions?

Answer 2

Programmer

Question 3

What is an exception handler?

Answer 3

Code section that gracefully responds to exceptions.

Question 4

What will happen when unhandled exceptions is running during runtime?

Answer 4

Crash a Program

Question 5

What is exception handling?

Answer 5

Process of intercepting and responding to exceptions to prevent crashes.

Question 6

From which class are all Error and Exception classes derived?

Answer 6

Throwable.

Question 7

Which two subclasses derive from Throwable?

Answer 7

1. Error
2. Exception.

Question 8

What are Error-derived classes for?

Answer 8

Critical JVM errors like out-of-memory; applications shouldn’t handle them.

Question 10

Which exceptions should programmers handle?

Answer 10

Those derived from Exception class (not Error).

Question 11

How do you handle exceptions in Java?

Answer 11

Use try block with one or more catch clauses.

Question 12

What is a try block?

Answer 12

Statements that might throw exceptions; application continues if caught.

Question 13

What is the syntax of a catch clause?

Answer 13

catch(ExceptionType name) { /* handler */ 
}

Question 14

What type can catch many exception subclasses?

Answer 14

A parameter of type Exception catches its subclasses.

Question 15

What errors handles error from Integer.parseInt()?

Answer 15

NumberFormatException

NumberFormatException class is derived from Exception class

Question 16

How must multiple catch clauses be ordered?

Answer 16

From most specific to most general.

JVM will run the first compatible catch clause found

Question 17

What happens when the JVM finds a compatible catch?

Answer 17

It runs the first compatible catch clause.

Question 18

Can we write 2 catch statements with the same Exception type?

Answer 18

No, below is wrong

try{
}catch(NumberFormatException e){
}catch(NumberFormatException e){
}

Question 19

What Java SE 7 feature reduces catch duplication?

Answer 19

Single catch statement can handle multiple exception types (multi-catch).

catch(InputMismatchException | NumberFormatException e){
}

Question 20

What is the finally clause?

Answer 20

Optional block executed after try and catch blocks.

Question 21

When is finally executed?

Answer 21

Always after try and catch, whether exception occurred or not.

try{
}catch(){
}finally{
}

System.out.println("Hello");

finally block always be executed
block outside will only be executed if it does not happen any exception

Question 22

Will finally execute if exception unhandled?

Answer 22

Yes; finally still executes unless JVM exits prematurely.

Will executes even have error

Question 23

List out 2 category of exceptions

Answer 23

1. Unchecked
2. Checked

Question 24

What are checked exceptions?

Answer 24

Non-Error, non-RuntimeException exceptions checked at compile time.

Occurs in Complie Time

Question 25

Give examples of checked exceptions.

Answer 25

1. IOException 2. SQLException, 3. ClassNotFoundException.

Question 26

What are unchecked exceptions?

Answer 26

Runtime exceptions from programming bugs; occur at runtime. ## Footnote Occurs in **Run Time**

Question 27

What's the difference: throws vs throw?

Answer 27

1. throws declares method may throw 2. throw actively throws an exception.

Question 28

Give examples of unchecked exceptions. ( 4 )

Answer 28

1. IllegalArgumentException 2. NullPointerException 3. ArithmeticException 4. ArrayIndexOutOfBoundsException

Question 29

What must a method do if it can throw checked exceptions?

Answer 29

Handle them or declare with throws in method header.

Question 30

How to manually throw an exception?

Answer 30

throw new ExceptionType("message");

Question 31

How to create a custom checked exception?

Answer 31

Extend Exception class.

Question 32

How to create a custom unchecked exception?

Answer 32

Extend RuntimeException class. ## Footnote ``` public class NegativeValueExceptions extends RuntimeException{ public NegativeValueExceptions(){ super("Negative Value"); } } ```

Question 33

Why create custom exceptions?

Answer 33

Represent domain-specific error conditions clearly.

Question 34

Give bank account custom exception scenarios.

Answer 34

1. Negative balance 2. Negative interest 3. Negative deposit 4. Withdraw exceeds Account's Balance.