Java Reference
In-Depth Information
Chapter 15
A Collection of Useful Classes
WHAT YOU WILL LEARN IN THIS CHAPTER
• How to use the static methods in the
Arrays
class for filling, copying, comparing, sorting, and
searching arrays
• How to use the
Observable
class and the
Observer
interface to communicate between objects
• What facilities the
Random
class provides
• How to create and use
Date
and
Calendar
objects
• What regular expressions are and how you can create and use them
• What a
Scanner
class does and how you use it
In this chapter you look at some more useful classes in the
java.util
package, but this time they are not
collection classes — just a collection of classes. You also look at the facilities provided by classes in the
java.util.regex
package that implement regular expressions in Java. Support for regular expressions is a
very powerful and important feature of Java.
UTILITY METHODS FOR ARRAYS
The
java.util.Arrays
class defines a set of static methods for operating on arrays. You have methods for
sorting and searching arrays, as well as methods for comparing arrays of elements of a basic type. You also
have methods for filling arrays with a given value. Let's look at the simplest method first, the
fill()
method
for filling an array.
Filling an Array
The need to fill an array with a specific value arises quite often, and you already met the static
fill()
method
that is defined in the
Arrays
class in Chapter 4. The
fill()
method comes in a number of overloaded ver-
sions of the form
fill(
type
[] array,
type
value)
Here
type
is a placeholder for the types supported by various versions of the method. The method stores
value
in each element of
array
. The return type is
void
so there is no return value. There are versions sup-
porting
type
as any of the following:
