Java Input and Output

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• Java Input and Output

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Java Input

• Input is any information needed by your program
  to complete its execution
• So far we have been using InputBox for this
• Examples of other Input
• Direct keyboard input
• Mouse
• Network
• Disk
• Microphone

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Java Output

• Output is any information that the program must
  convey to the user
• So far we have been using OutputBox and
  System.out.println()
• Examples of other Output
• printer
• Network
• Disk
• Speakers

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Java I/O

• We have been using the javabook2 package because
  its easier
• Its easier because it eliminates a lot of errors
• Ex. NumberFormatException occurs if user enters
  letters when a number is expected
• getInteger() checks for this
• It is also easier because it is simple
• Getting numbers, Strings, etc. is straightforward
• These actions become much more complex without
  javabook
• Standard java classes are not as simple because
  they offer added flexibility. Flexibility comes
  at the cost of increasing complexity.

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Java Console Input

• Remember Console window is the black window that
  is automatically launched when you run your
  program
• We havent used this to get input so far
• There are three parts to getting console input
• Prompt the user
• Get this input
• Convert the input

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Java Console Input

• Prompt the user
• The user must be told to enter information
• The user will only know what type of information
  to enter if you tell them

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Java Console Input

• Get the input
• Several standard classes are helpful
• java.io.InputStream Stores information about
  the connection between an input device and your
  program
• java.io.InputStreamReader used to translate
  data bytes received from InputStream objects into
  a stream of characters
• Java.io.BufferedReader used to buffer (store)
  input received from an InputStreamReader object
  (stores input as strings).

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Java Console Input

• None of these classes has a method as simple as
  getString
• BufferedReader has readLine() which returns a
  string
• So lets make a BufferedReader
• Look at the constructor online
• We need a Reader object

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Java Console Input

• InputStreamReader extends
• the Reader class
• Extends means
• Robin extends bird
• Robin is a bird,
• bird is not necessarily a robin
• If you need a bird, a robin will do
• We will use an InputStreamReader for our reader
  (Because we want an InputStream)
• Look at constructor for InputStreamReader
• We need an InputStream object

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Java Console Input

• The System class in the java.lang package (which
  is automatically imported) automatically creates
  an InputStream object for us called in
• We can access it with System.in
• This InputStream is connected to the keyboard
• We can use it to create our InputStreamReader
  object, which we can use to create our
  BufferedReader object

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Java Console Input

• Put it all together
• 1. Use System.in to create an InputStreamReader
  object
• 2. Use the InputStreamReader object to create a
  BufferedReader object
• 3. Display a prompt to the user for the desired
  data
• 4. Use the BufferedReader object to read a line
  of text from the user
• 5. Convert/use the input received

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Java Console Input

• // 1. Use System.in to create an
  InputStreamReader object
• InputStreamReader isr new InputStreamReader(Syst
  em.in)
• // 2. Use the InputStreamReader object to create
  a
• // BufferedReader object
• BufferedReader stdin new BufferedReader(isr)
• // 3. Display a prompt to the user for the
  desired data
• System.out.print(Johnny 5 needs more input)
• // 4. Use the BufferedReader object to read a
  line of text from the user
• String input stdin.readLine()
• // 5. Convert/use the input received
• System.out.println(You typed input)

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Java Console Input

• Questions??

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Java Console Input

• // 1. Use System.in to create an
  InputStreamReader object
• InputStreamReader isr new InputStreamReader(Syst
  em.in)
• // 2. Use the InputStreamReader object to create
  a
• // BufferedReader object
• BufferedReader stdin new BufferedReader(isr)
• // 3. Display a prompt to the user for the
  desired data
• System.out.print(Johnny 5 needs more input)
• // 4. Use the BufferedReader object to read a
  line of text from the user
• String input stdin.readLine()
• // 5. Convert/use the input received
• System.out.println(You typed input)

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Java Console Input

• Dont forget to import java.io.
• Shorter version
• BufferedReader stdin new BufferedReader( new
  InputStreamReader (System.in) )

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Java Console Input

• Converting input is sometimes necessary
• String input stdin.readLine()
• // user enters 123
• int number Integer.parseInt(input)
• This can cause Exceptions
• Look at the Integer class online

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Java Console Input

• Questoins??

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Java Console Output

• We have used System.out.println() as an
  alternative to OutbutBox and Message box of
  javabook2
• This console output displays a String of
  characters
• System.out is an instance of the PrintStream class

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Java Console Output

• A Stream object is used to store information
  needed to connect a computer program to an input
  or output device
• Just like a Reader object adds functionality to
  an InputStream, a Printer object adds
  functionality to an OutputStream
• Console output is easy in java because printer
  methods (print and println) can handle many types
  of input

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Java Console Output

• int x 3
• char a a
• boolean r true
• String phrase Cats meow
• System.out.println(x)
• System.out.println(a)
• System.out.println(r)
• System.out.println(phrase)

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java.lang.System

• java.lang.System automatically creates three
  streams for your program
• System.in - InputStream
• System.out - PrintStream
• System.err - PrintStream

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Java Console Output

• Questions????

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Printing objects

• In java, you can print anything
• Wanderer w new Wanderer(Gil,Color.green)
• System.out.println(w)
• This prints
• Wanderer_at_13fac
• This is a memory location (it is not very useful)

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Printing objects

• In java, all objects have a toString( ) method
• It is inherited from the Object object
• You can override it by writing your own toString(
  ) for your class
• public String toString( )
• String coords ( myLoc.getX() ,
  myLoc.getY() )
• return myName is at coords

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Printing objects

• Now,
• Wanderer w new Wanderer(Gil,Color.green)
• System.out.println(w)
• Will print
• Gil is at (11,9)
• This is Useful!
• It can help you display output easily and debug
  your program