Introduction to I/O and Networking

Question 1

Exception

Answer 1

An exception is an object of type Exception

Question 2

Checked exceptions

Answer 2

Compiler-checked exceptions. All other exceptions besides RuntimeException must be check

Question 3

“finally” keyword

Answer 3

Where you put code that must run regardless of an exception

Question 4

If the try block fails (an exception)

Answer 4

Flow control immediately moves to the catch block. When the catch block completes, the finally block runs, When the finally block completes, the rest of the method continues on

Question 5

If the try block succeeds (No exception)

Answer 5

Flow control skips over the catch block and moves to the finally block. When the finally block completes, the rest of the method continues on

Question 6

If the try or catch block has a return statement, finally will still run

Answer 6

Flow jumps to the finally, then back to the return

Question 7

A method can throw more than one exception?

Answer 7

Yes, if it darn well needs to. But a method’s declaration must declare all the checked exceptions it can throw

Question 8

Exception are polymorphic

Answer 8

Exceptions are objects. The benefit for exceptions is that a method doesn’t have to explicitly declare every possible exception it might throw

Question 9

Exception rules

Answer 9

1. You cannot have a catch or finally without a try
2. A try must be followed by either a catch or a finally
3. You cannot put code between the try and the catch
4. A try with only a finally (no catch) must still declare the except

Question 10

Serialization

Answer 10

Write a file that holds flattened objects. Then have your program read the serialized objects from the file and inflate them back into living, breathing, heap-inhabiting objects

Question 11

The mother of all catch argument is type Exception

Answer 11

It will catch any exception, including runtime exceptions, so you probably won’t use it outside of testing

Question 12

Fundamental I/O tehcnique

Answer 12

1. Write some data to something

2. Read some data from either a file on disk or a network connection

Question 13

Connection

Answer 13

Streams represent a connection to a source or destination (file, socket) while chain streams can’t connect on their own and must be chained to a connection stream

Question 14

Serialization saves the entire object graph

Answer 14

All objects referenced by instance variables, starting with the object being serialized

Question 15

Serializable interface

Answer 15

Known as a marker or tag interface, because the interface doesn’t have any methods to implement

Question 16

Transient

Answer 16

If an instance variable can’t be saved

Question 17

Deserialization

Answer 17

To restore it back to its original state at some later date, in a different ‘run’ of the JVM

Question 18

Are static variables serialized?

Answer 18

No. Static means “one per class” not “one per object”. Static variables are not saved, and when an object is deserialized, it will have whatever static variable its class currently has.

Question 19

java.io.File

Answer 19

represents a file on disk, but doesn’t actually represent the contents of the file

Question 20

File object

Answer 20

represents the name and path of a file or directory on disk. But it does NOT represent, or give you access to, the data in the file

Question 21

The difference between with bufferedWriter and without bufferedWriter

Answer 21

BufferedWriter hold all the stuff you write to it until it’s full. Without BufferedWriter, we would have to write each and everything we pass to the file each and every time

Question 22

How many can one method throw?

Answer 22

Multiple exceptions if it needs to

Question 23

What is the mother of all catch arguments?

Answer 23

Exception; it will catch any exception, including runtime (unchecked) exceptions, so you probably won’t use it outside of testing

Question 24

Why can’t you put bigger exceptions on top of smaller exception?

Answer 24

The compiler knowns there’s no point in adding any other exceptions

Question 25

MidEvent

Answer 25

An instruction for part of a song. It says what to do and when to do it.

Question 26

A try block must be followed by a catch and a finally block

Answer 26

False, either or both

Question 27

If you write a method that might cause a compiler-checked exception, you must wrap that risky code in a try / catch block

Answer 27

False, you can declare the exception

Question 28

Catch blocks can be polymorphic

Answer 28

True, because it’s impossible to identify all the exceptions

Question 29

Only ‘compiler checked’ exceptions can be caught

Answer 29

False, runtime exception can be caught

Question 30

If you define a try/catch block, a matching finally block is optional

Answer 30

True

Question 31

If you define a try block, you can pair it with a matching catch or finally block, or both

Answer 31

True, both are acceptable

Question 32

If you write a method that declares that it can throw a compiler-checked exception, you must also wrap the exception throwing code in a try/catch block

Answer 32

False, the declaration is sufficient

Question 33

The main method in your program must handle all unhandled exceptions thrown to it

Answer 33

False, but if it doesn’t the JVM may shut down

Question 34

Handling an exception is sometimes referred to as ‘ducking’

Answer 34

False, ducking is synonymous with declaring

Question 35

A method with a try block and a finally block, can optionally declare the exception

Answer 35

False, if you don’t have a catch block, you must declare