Transcript Console Output

Console Output in Java
Notes Supplement
CS 1054 Introduction to Programming in Java
Spring 2008
print() and println()
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So far, we’ve used System.out.print and
System.out.println for output
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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
1: Output
Slide 2
Printing values around strings
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Suppose we wanted to print the values of two
variables, numCones (int) and unitPrice (double),
in a neat message
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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
1: Output
Slide 3
String concatenation
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Can use the + operator on strings
If both arguments are strings, it is simply
concatenated or “put together”, e.g.,
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"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
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"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
1: Output
Slide 4
Using concatenation with
print and println
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Improved version
System.out.print("sold " + numCones );
System.out.println( " cones at " +
unitPrice + " each." );
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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
1: Output
Slide 5
String formatting
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Notice that particularly with floating point
numbers, we have no control over how many
spaces are occupied by a number when printed
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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
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Can be done in Java using the printf() method
Introduction to Object-Oriented Programming
1: Output
Slide 6
The printf() method
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Even better version:
System.out.printf(
"sold %d cones at %.2f each.\n",
numCones, unitPrice );
\n means a newline,
same effect as
println()
prints: 5 cones sold at 2.50 each
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More control:
System.out.printf(
"sold %3d cones at %6.2f each.\n",
numCones, unitPrice );
prints: ˍˍ5 cones sold at ˍˍ2.50 each
Introduction to Object-Oriented Programming
1: Output
Slide 7
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
1: Output
Slide 8
Format specifier
System.out.printf("pi = %6.3f \n", pi);
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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
1: Output
Slide 9
Conversion options
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%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
1: Output
Slide 10