Java Reference
In-Depth Information
One package requires no import statement. The package
java.lang
contains classes
that are fundamental to Java programming. These classes are so basic that the package
is always imported automatically. Any class in
java.lang
does not need an import
statement to make it available to your code. So, when we say that a class is in the
package
java.lang
, you can simply use that class in your program without needing
any import statement. For example, the class
String
is in the
java.lang
package, so
you can use it without any import statement.
More material on packages is covered in Chapter 5 .
java.lang
Self-Test Exercises
8. What output is produced by the following code? (Assume a proper
import
statement has been given.)
NumberFormat exerciseFormatter =
NumberFormat.getCurrencyInstance(Locale.US);
double
d1 = 1.2345, d2 = 15.67890;
System.out.println(exerciseFormatter.format(d1));
System.out.println(exerciseFormatter.format(d2));
9. Suppose the class
Robot
is a part of the standard Java libraries and is in the
package named
java.awt
. What
import
statement do you need to make the
class
Robot
available to your program or other class?
The
DecimalFormat
Class
★
System.out.println
will let you output numbers but has no facilities to format the
numbers. If you want to output a number in a specific format, such as having a specified
number of digits after the decimal point, then you must convert the number to a string
that shows the number in the desired format and then use
System.out.println
to output the string. Earlier in this chapter, we saw one way to accomplish this for
amounts of money. The class
DecimalFormat
provides a versatile facility to format
numbers in a variety of ways.
The class
DecimalFormat
is in the Java package named
java.text
. So you must
add the following (or something similar) to the beginning of the file with your program
or other class that uses the class
DecimalFormat
:
import
import
java.text.DecimalFormat;
An object of the class
DecimalFormat
has a number of different methods that can
be used to produce numeral strings in various formats. In this subsection, we discuss
one of these methods, which is named
format
. The general approach to using the
format
method is discussed in the following pages.
Create an object of the class
DecimalFormat
, using a
String
Pattern
as follows:
DecimalFormat
Variable_Name
=
new
DecimalFormat(
Pattern
);
patterns