Learning Java, 6th Edition

Chapter 8. Text and Core Utilities

If you’ve been reading this book sequentially, you’ve read all about the core Java language constructs, including the object-oriented aspects of the language and the use of threads. Now it’s time to shift gears and start talking about the collection of classes that compose the standard Java packages and come with every Java implementation. Java’s core packages are one of its most distinguishing features. Many other object-oriented languages have similar features, but none has as extensive a set of standardized classes and tools as Java does. This is both a reflection of—and a reason for—Java’s success.

Strings

We’ll start by taking a closer look at the Java String class (or, more specifically, java.lang.String). Because working with Strings is so fundamental, it’s important to understand how they are implemented and what you can do with them. A String object encapsulates a sequence of Unicode characters. Internally, these characters are stored in a regular Java array, but the String object guards this array jealously and gives you access to it only through its own API. This is to support the idea that Strings are immutable; once you create a String object, you can’t change its value. Lots of operations on a String object appear to change the characters or length of a string, but what they really do is return a new String object that copies or internally references the needed characters of the original. Java implementations make an effort to ...