Ivor Horton's Beginning Java®, Java 7 Edition

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 versions of the form

fill(type[] array, type value) ...