Week 11

Question 1

An abnormal conditon or an error that disrupts the normal flow of a program

Answer 1

An exception

Question 2

Allows the program to continue executing after an exception occurs

Answer 2

Exception handling

Question 3

Common examples of exceptions

Answer 3

Out of range array indices, arithmetic overflow, division by 0, invalid method params

Question 4

What is a synchronous error?

Answer 4

Errors that occur when a statement executes - typically associated with runtime errors that detected during execution (out of bounds array, division by 0)

Question 5

What are asynchronous events?

Answer 5

They occur independently of the main program flow. They’re associated with external events, like disk I/O completions, network message arrivals, or user inputs like mouse clicks/keystrokes

Question 6

Why is exception handling important from the earliest stages of design?

Answer 6

It’s important for robust and fault-tolerant programs. Going back and adding it later is expensive, time-consuming, and likely difficult.

Question 7

What does the “throws” keyword do?

Answer 7

Indicate that the method may throw exception(s). When “throws” is seen it means the caller of the method has to be responsible for handling the exception, because it likely doesn’t handle any itself.

Question 8

What is the purpose of the finally block?

Answer 8

Specifies a section of the code that MUST be executed, regardless of whether an exception is thrown or caught.

It’s typically used for cleanup or resource release operations. I.E. closing a file or releasing a DB connection

Question 9

What are checked exceptions?

Answer 9

Exceptions that are checked at compile time. These exceptions are directly derived from the Throwable class, except for RunTImeException and Error.

Question 10

Name checked exceptions

Answer 10

IOException, ClassNotFoundException, SQLException, SocketExceptoon, FileNotFoundException

Question 11

Name unchecked exceptions

Answer 11

Error, RunTime Exception and all of its children (NullPointer, ClassCast, Arithmetic, DateTime, ArrayStore)

Question 12

FileNotFoundException inherits from IOException, what catch clause can be used to catch a FileNotFoundException

Answer 12

IOException

Question 13

When does a method terminate and not return a value?

Answer 13

When it throws an exception

Question 14

What happens to local variables when a method throws an exception but does not catch it in scope

Answer 14

They go out of scope, the method-call stack is “unwound”

Question 15

What is stack unwinding?

Answer 15

When an exception is thrown but not caught in a particular scope the method-call stack is “unwound”

Question 16

What happens after stack unwinding?

Answer 16

Attempt to catch the exception the next outer try block

Question 17

What is unique about printStackTrace and getStackTrace? (both methods of Java’s “Throwable” Class). Why is this sometimes a problem?

Answer 17

They process the entire method-call stack. When debugging this can be inefficient

Question 18

If a catch block throws a new exception, what happens to the original exception?

Answer 18

The exception and stack trace are lost

Question 19

What allows an exception object to maintain the complete stack-trace info from the original exception?

Answer 19

Chained exceptions

Question 20

How do you get the throwable method that initially caused the exception?

Answer 20

By calling the “Throwable” method getCause()