String Formatting Preparing strings for output

Printing println( arg ) prints its one argument on a line println can be used to print any single value, but it doesn’t work well with arrays or user-defined data types scala> println(List(1, 2, 3)) List(1, 2, 3) scala> println(Array(1, 2, 3)) When printing a user-defined type, println will first look to see if you have written a toString method that it can use You can use println without an argument to get a blank line print( arg ) works like println, but doesn’t go to the next line scala> print("abc"); print("xyz") abcxyz 2

Concatenation The simplest way to print several values at once is to “add” (concatenate) them with a string, with the + operator When a value is concatenated with a string, the value’s toString method is called scala> println("Array is " + Array(1, 2, 3) + ", List is " + List(1, 2, 3)) Array is List is List(1, 2, 3) When you study classes, you will learn how to write your own toString methods 3

Interpolation You can insert (interpolate) the value of simple variables into strings by doing two things: Prefix the string with an s Put a $ before the variable name Example: s"Your score is $score" You can also interpolate the value of expressions by enclosing them in curly braces after the $ Example: s"Twice $x is ${2 * x}" 4

Formatting I Sometimes you want more precise control over the way numbers and dates are printed Default: scala> println(7 * 0.1) scala> println(new java.util.Date) Sat Jul 20 12:59:33 PDT 2013 Formatted: scala> println("Seven tenths is %5.3f".format(7 * 0.1)) Seven tenths is scala> println("Today's date is %tD".format(new java.util.Date)) Today's date is 07/20/13 5

Formatting The syntax is: string.format( value, …, value ) The number and types of values must agree with the format specifiers Here are examples of the most common format specifiers %12d format an integer right-justified in a field of width 12 %-8d format an integer left-justified in a field of width 8 %5.3f format a floating point number right-justified in a field of width 5, with 3 digits after the decimal point %12.3e like %12.3f, but using scientific ( E ) notation %7b format a boolean right-justified in a field of width 7 %10s format a string right-justified in a field of width 10 If a field width is too small, will be ignored Irregular spacing is better than printing the wrong number! 6

printf printf( string, value, …, value ) is shorthand for print( string.format( value, …, value )) Note that this is a shorter way to call print, not println To do the equivalent of a println, put a \n as the last character in the string 7

8 The End