Miscellaneous topics

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Miscellaneous topics

• Chapter 2 Savitch

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Miscellaneous topics

• Standard output using System.out
• Input using Scanner class

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The standard System class

• System contains a number of interesting static
  methods.
• System.exit( 0 )
• Terminates our program immediately
• long start System.currentTimeMillis()
• Useful for timing programs
• System.out and System.in
• The standard output and input streams
• See http//java.sun.com/j2se/1.5.0/docs/api/java/l
  ang/System.html

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Output and System.out
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System.out

• Static member (not a method)
• Type is PrintStream
• See http//java.sun.com/j2se/1.5.0/docs/api/java/i
  o/PrintStream.html
• Useful PrintStream methods
• print()
• println()
• printf()

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print() and println()

• print() prints its argument
• println() prints its argument followed by a
  newline
• Ex.
• int i12
• String s sally
• System.out.println( i )
• System.out.print( s is i years old.
  )
• System.out.println()

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printf()

• What about floating point numbers?
• Run jGRASP now.
• Try the following
• double d 12.99134267
• System.out.println( d )
• d12.00000000
• System.out.println( d )
• What is the output?

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printf()

• Definition of printf
• public PrintStream printf ( String format,
  Object... args )
• From http//java.sun.com/j2se/1.5.0/docs/api/java/
  io/PrintStream.htmlprintf(java.lang.String,20jav
  a.lang.Object...)

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printf()

• Format string examples
• d 12.00000
• System.out.printf( .2f, d )
• System.out.println()
• d 12.99999999
• System.out.printf( .2f, d )
• System.out.println()
• See http//java.sun.com/j2se/1.5.0/docs/api/java/u
  til/Formatter.htmlsyntax for the full definition.

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printf()

• Format string examples
• d 12.00000
• System.out.printf( 10.2f, d )
• System.out.println()
• d 12.99999999
• System.out.printf( 10.2f, d )
• System.out.println()

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printf()

• Format string examples
• d 12.00000
• System.out.printf( 10.2f n, d )
• d 12.99999999
• System.out.printf( 10.2f n, d )

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printf()

• Format string examples
• d 12.00000
• System.out.printf( 010.2f n, d )
• d 12.99999999
• System.out.printf( 010.2f n, d )

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printf()

• Format string examples
• d 12.00000
• System.out.printf( -10.2f feet.n, d )
• d 12.99999999
• System.out.printf( -10.2f feet.n, d )

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printf()

• Useful for formatting other data types as well.
• int i 22
• System.out.printf( "d n", i )
• System.out.printf( "6d n", i )
• System.out.printf( "06d n", i )
• System.out.printf( "-6d n", i )
• System.out.printf( "x n", i )

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printf()

• Useful for Strings too.
• String s "sally"
• System.out.printf( "s eats here.n", s )
• System.out.printf( "12s eats here.n", s )
• //exception thrown
• //System.out.printf( "012s eats here.n", s )
• System.out.printf( "-12s eats here.n", s )

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More OO alternatives to printf()

• NumberFormat
• DecimalFormat

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Input, System.in, and the Scanner class
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Scanner class

• Note that System.in is of type InputStream (see
  http//java.sun.com/j2se/1.5.0/docs/api/java/io/In
  putStream.html).
• And the InputStream can only read arrays of
  bytes! How can we read ints, floats, doubles,
  etc.?
• Use the Scanner class.

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Scanner class

• import java.util.Scanner
• class Tester
• public static void main ( String params )
• Scanner kbd new Scanner( System.in )

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Scanner class

• Scanner kbd new Scanner( System.in )
• System.out.println( Enter weight and age )
• int weight kbd.nextInt()
• int age kbd.nextInt()
• System.out.println( Thanks. )

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Some useful Scanner class methods

• nextInt()
• nextLong()
• nextByte()
• nextShort()
• nextDouble()
• nextFloat()

• hasNextInt()
• hasNextLong()
• hasNextByte()
• hasNextShort()
• hasNextDouble()
• hasNextFloat()

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More useful scanner class methods

• nextBoolean() (and hasNextBoolean())
• Response should be either true or false
• next() (and hasNext())
• Returns a string of the next characters up to but
  not including the next whitespace character
• nextLine() (and hasNextLine())
• Returns a string of the next characters upt to
  but not including the next newline character

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Exercises on p. 91