CS 1054 Introduction to Programming in Java Console Output in Java Notes Supplement CS 1054 Introduction to Programming in Java Spring 2008

Introduction to Object-Oriented Programming print() and println() So far, we’ve 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 Introduction to Object-Oriented Programming

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." ); Introduction to Object-Oriented Programming

Introduction to Object-Oriented Programming 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 Introduction to Object-Oriented Programming

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) Introduction to Object-Oriented Programming

Introduction to Object-Oriented Programming 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 Introduction to Object-Oriented Programming

Introduction to Object-Oriented Programming 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: ˍˍ5 cones sold at ˍˍ2.50 each \n means a newline, same effect as println() Introduction to Object-Oriented Programming

Introduction to Object-Oriented Programming System.out.printf() // prints PI with 3 decimal places // 6 spaces total: ˍ3.142 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 Introduction to Object-Oriented Programming

Introduction to Object-Oriented Programming 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 Introduction to Object-Oriented Programming

Introduction to Object-Oriented Programming 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 Introduction to Object-Oriented Programming