Console Output in Java

1
Console Output in Java

• Notes Supplement
• CS 1054 Introduction to Programming in Java
• Spring 2008

2
print() and println()

• So far, weve used System.out.print and
  System.out.println for output
• With a single argument(string or numeric value)
• println() if we require a new line at the end of
  the output
• print() to stay on the current output line

3
Printing values around strings

• Suppose we wanted to print the values of two
  variables, numCones (int) and unitPrice (double),
  in a neat message
• e.g., sold 5 cones at 2.50 each.
• Using print and println,
• System.out.print("sold " )
• System.out.print( numCones )
• System.out.print( " cones at " )
• System.out.print( unitPrice )
• System.out.println(" each." )

4
String concatenation

• Can use the operator on strings
• If both arguments are strings, it is simply
  concatenated or put together, e.g.,
• "Basket" "ball" equals "Basketball"
• "Hi, " name equals "Hi, Bob" assuming name has
  the value "Bob"
• If one argument is a number, that argument is
  converted to a string
• "Hi, " 5 equals "Hi, " "5" "Hi, 5"
• "Price " unitPrice equals "Price 2.50"
  assuming price has the value 2.50

5
Using concatenation with print and println

• Improved version
• System.out.print("sold " numCones )
• System.out.println( " cones at " unitPrice "
  each." )
• Can actually be compressed into one println
  statement
• Note that the print or println method still has
  one argument even in these cases(a string)

6
String formatting

• Notice that particularly with floating point
  numbers, we have no control over how many spaces
  are occupied by a number when printed
• e.g., 5 cones sold at 2.4999998 each
• What would be preferable is to be able to
  indicate up to how many decimal places are
  allowed
• Can be done in Java using the printf() method

7
The printf() method

• Even better version
• System.out.printf("sold d cones at .2f
  each.\n",numCones, unitPrice )
• prints 5 cones sold at 2.50 each
• More control
• System.out.printf("sold 3d cones at 6.2f
  each.\n",numCones, unitPrice )
• prints __5 cones sold at __2.50 each

\n means a newline, same effect as println()
8
System.out.printf()

• // prints PI with 3 decimal places
• // 6 spaces total _3.142 including the .
• public class PrintingPI
• public static void main( String args )
• double pi Math.PI
• System.out.printf("pi 6.3f \n", pi)

Format specifier
9
Format specifier

• System.out.printf("pi 6.3f \n", pi)
• The symbol signifies the start of the specifier
• 6 means that the width of the number is 6
  characters (including the . pad with leading
  spaces if needed)
• The precision value 3 means that 3 decimal places
  are required
• The conversion character f means that the
  corresponding argument is a floating-point number
• \n results in a line break

10
Conversion options

• 10.3f use f for float and double, first number
  is the width, second number is the number of
  decimal places
• 5d use d for integer types, the number
  indicates the width
• 10s use s for strings, the number indicates
  the width
• d f s with no numbers indicated means you
  are leaving the formatting to Java defaults