Scanner class

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Scanner class

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Scanner is a class for reading from devices

• Readable
• any object that implements the Readable()
  interface
• a Readable is a source of characters made
  available to callers of the read method via a
  CharBuffer, usually with underlying get and put
  methods
• ReadableByteChannel
• a ReadableByteChannel object represents an open
  connection to a hardware device, a file, a
  network socket, or a program component that is
  capable of performing reading or writing bytes.
• InputStream
• InputStream is new InputString(System.in) //
  console
• File
• String

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constructors

• Scanner(InputStream source)
• Scanner(InputStream source, String charsetName)
• scan values from the specified input stream
• Scanner(File source)
• Scanner(File source, String charsetName)
• scan values from the specified file
• Scanner(String source)
• scan values from the specified string
• Scanner(Readable source)
• scan values from the specified object (that
  implements the Readable interface)
• Scanner(ReadableByteChannel source)
• Scanner(ReadableByteChannel source, String
  charsetName)
• scan values from the specified channel

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java.util.Scanner

• Scanner
• extends Object
• implements IteratorltStringgt
• a text parser for primitives and strings
• can use regular expressions
• breaks its input into tokens using a delimiter
  pattern
• by default matches whitespace
• resulting String tokens may then be read
• can perform automatic type conversion upon reading

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read a number from System.in

• Scanner sc new Scanner(System.in)

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read long values from a file

• Scanner sc
• new Scanner( new File("myNumbers")
  )
• while ( sc.hasNextLong() )
• long aLong sc.nextLong()

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use delimiters other than whitespace

• String input "1 fish 2 fish red fish blue
  fish"Scanner s new Scanner(input).useDelim
  iter("\\sfish\\s")System.out.println(s.nextInt
  ()) System.out.println(s.nextInt())System.out.
  println(s.next())System.out.println(s.next())
  s.close()

output 1 2 red blue
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use a regular expression to parse tokens

• String input "1 fish 2 fish red fish blue
  fish"Scanner s new Scanner(input)s.findInLin
  e( "(\\d) fish (\\d) fish (\\w) fish
  (\\w)) MatchResult result s.match() for
  (int i1 iltresult.groupCount() i)
  System.out.println(result.group(i)) s.close()

output 1 2 red blue
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after use, the Scanner must be closed

• Scanner sc new Scanner(System.in)
• // do something with the Scanner
• in.close()

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