Java IO Fundamentals

Question 1

what does the public static field “in” of java.lang.System class represents and what type is it?

Answer 1

Represent standard input and is of type java.io.InputStream

Question 2

what does the public static field “out” and “err” of java.lang.System class represents and what type are they?

Answer 2

output and error streams. They are of type java.io.PrintStream

Question 3

if you do not provide the intended input data type as expect by the format string, what exception you may get?

Answer 3

IllegalFormatConversionException

Question 4

Whats the difference between Character Stream and Byte Streams?

Answer 4

• Character streams are meant for reading or writing to a character- or text-based IO such as text files, text documents, XML and HTML files while Byte Streams are meant for reading or wiriting to a binary data IO such as executable files, image files, and files in low level file format such as .zip, .class, .exe..
• Character streams data is dealt with 16-bit unicode class while Byte Streams is dealt with 1 byte (8 bits)
• For Character stream Input and output character streams are called readers and writers, while input and and output byte streams are called input streams and output streams
• Character streams uses abstract classes of Reader and Writer, for Byte Streams its classes are called InputStream and OutputStream

Question 5

give a short description of the class StringReader deriving from the reader class

Answer 5

character stream that operates on a string

Question 6

give a short description of the class InputStreamReader deriving from the reader class

Answer 6

bridge between character stream and byte streams

Question 7

give a short description of the class FileReader deriving from the reader class

Answer 7

devired class of InputStreamReader that provides support for reading character files

Question 8

give a short description of the class BufferedReader deriving from the reader class

Answer 8

adds buffering to the underlying character stream so there is no need to access the underlying file system for each read and write operation

Question 9

give a short description of the class StringWriter deriving from the Writer class

Answer 9

a character stream that collects the output in a string buffer, which can be used for creating a string

Question 10

give a short description of the class OutputStreamWriter deriving from the Writer class

Answer 10

this class is a bridge between character streams and byte streams

Question 11

give a short description of the class FileWriter deriving from the Writer class

Answer 11

derived class of OutputStreamWriter that provides support for writing character files

Question 12

give a short description of the class PrintWriter deriving from the Writer class

Answer 12

supports formatted printing of characters to the output character stream

Question 13

What is the difference between Streams and Reader/Writers?

Answer 13

• The Stream classes are used for inputting all types of binary/byte data
• Reader and writers classes are used for inputting and outputting only characters and string data

Question 14

Does PrintWriter has a PrintReader?

Answer 14

False

Question 15

What are the four abstract classes that are parent of all Stream Classes?

Answer 15

• InputStream
• OutputStream
• Reader
• Writer

Question 16

What are the classes that extend from InputStream?

Answer 16

• FileInputStream (low level)
• FilterInputStream
  
  • BufferedInputStream (extends FilterInputStream)
• ObjectInputStream

Question 17

Which are the classes that extend from Reader?

Answer 17

• BufferedReader
• InputStreamReader
  
  • File Reader ( extends from InputStreamReader) (low level)

Question 18

Which are the classes that extend from OutputStream?

Answer 18

• FileOutputStream (low level)
• FilterOutputStream
  
  • BufferedOutputStream (extend from FilterOutputStream)
  • PrintStream(extend from FilterOutputStream)
• ObjectOutputStream

Question 19

Which classes classes extend from Writer?

Answer 19

• BufferedWriter
• OutputStreamWriter
  
  • FileWriter (low level)
• PrintWriter

Question 20

What does System.in return?

Answer 20

InputStream

Question 21

What does System.out return?

Answer 21

PrintStream

Question 22

The console class provides access to which instances?

Answer 22

Reader and PrintWriter using the methods reader() and writer() respectively

Question 23

(Console)

What does the readLine() method do?

Answer 23

Retrieves a single line of text from the user and the user press enter to terminate it

Question 24

(Console)

What does the readPassword() return?

Answer 24

Array of characters

Question 25

True or false

Most methods in the File class that interacts with the file system are capable of throwing an exception at runtime

Answer 25

True

Question 26

If we want to move a file using File, what method do we have to use?

Answer 26

renameTo() since there are no move() or mv() methods

Question 27

If we want to create a directory using File class, what method do we have to use?

Answer 27

mkdir() or mkdir(), since there are no createDirectory() method

Question 28

What are the two output methods that the console class has?

Answer 28

format() and printf(), there is no println or out methods

Question 29

What does the method isReady from Reader do?

Answer 29

The ready method just checks if there are more bytes available to read

Question 30

In which case can the Console object be acquired?

Answer 30

when the JVM is started from the interactive command line without redirecting the standard input and output streams