Mastering Java System Output and Input: A Guide to System.out and Scanner Class

1. Miscellaneous topics Chapter 2 Savitch

2. Miscellaneous topics • Standard output using System.out • Input using Scanner class

3. 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/lang/System.html

4. Output and System.out

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

6. print() and println() • print() prints its argument • println() prints its argument followed by a newline • Ex. int i=12; String s = “sally”; System.out.println( i ); System.out.print( s + “ is “ + i + “ years old.” ); System.out.println();

20. printf and rounding • What is the output of the following: class Test { public static void main ( String args[] ) { double d2 = 12.999999; System.out.printf( "%f %.2f \n\n", d2, d2 ); } }

21. printf and rounding • What is the output of the following: class Test { public static void main ( String args[] ) { double d2 = 12.999999; System.out.printf( "%f %.2f \n\n", d2, d2 ); } } 12.999999 13.00

22. printf() • Format string examples: d = 12.00000; System.out.printf( “%010.2f %n”, d ); d = 12.99999999; System.out.printf( “%010.2f %n”, d );

23. 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 );

24. 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 );

25. More OO alternatives to printf() • NumberFormat • DecimalFormat

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

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

28. Scanner class import java.util.Scanner; class Tester { public static void main ( String params[] ) { Scanner kbd = new Scanner( System.in ); … } }

29. 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.” );

30. nextInt() nextLong() nextByte() nextShort() nextDouble() nextFloat() hasNextInt() hasNextLong() hasNextByte() hasNextShort() hasNextDouble() hasNextFloat() Some useful Scanner class methods

31. 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

32. Exercises on p. 91