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

2. 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

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." );
Introduction to Object-Oriented Programming

4. 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

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)
Introduction to Object-Oriented Programming

6. 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 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

7. 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

8. 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

9. 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

10. 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