Java Reference
In-Depth Information
tem.out.println()
is of type
PrintStream
. This class outputs data of any of the basic types as a string.
For example, an
int
value of
12345
becomes the string
"12345"
as generated by the
valueOf()
method
from the
String
class. However, you also have the
PrintWriter
class that I discussed earlier in the chapter
to do the same thing because this class has all the methods that
PrintStream
provides.
The principle difference between the two classes is that with the
PrintWriter
class you can control
whether or not the stream buffer is flushed when the
println()
method is called, whereas with the
PrintStream
class you cannot. The
PrintWriter
class flushes the stream buffer only when one of the
println()
methods is called, if automatic flushing is enabled. A
PrintStream
object flushes the stream
buffer whenever a newline character is written to the stream, regardless of whether it was written by a
print()
or a
println()
method.
Both the
PrintWriter
and
PrintStream
classes format basic data as characters. In addition to the
print()
and
println()
methods that do this, they also define the
printf()
method mentioned in Chapter
6. This method gives you a great deal more control over the format of the output and also accepts an arbit-
rary number of arguments to be formatted and displayed.
The printf() Method
The
printf()
method that is defined in the
PrintStream
and
PrintWriter
classes produces formatted out-
put for an arbitrary sequence of values of various types, where the formatting is specified by the first argu-
ment to the method.
System.out
happens to be of type
PrintStream
, so you can use
printf()
to produce
formatted output to the command line. The
PrintStream
and
PrintWriter
classes define two versions of
DESCRIPTION
Outputs the values of the elements in
args
according to format specifications in
format
. An excep-
tion of type
NullPointerException
is thrown if
format
is
null
.
printf(String
format,
Object ...
args)
This version works as the preceding version does except that the output is tailored to the locale speci-
fied by the first argument. I explain how you define objects of the
java.util.Locale
class type a
little later in this chapter.
printf(Locale
loc,
String
format,
Object ...
args)
The
format
parameter is a string that should contain at least one format specification for each of the ar-
gument values that follow the format argument. The format specification for an argument value just defines
how the data is to be presented and is of the following general form:
%[argument_index$][flags][width][.precision]conversion
The square brackets around components of the format specification indicate that they are optional, so the
minimum format specification if you omit all of the optional parts is
%conversion
.
