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Trail: Learning the Java Language
Lesson: Numbers and Strings
Section: Strings
Numbers and Strings
Numbers
The Numbers Classes
Formatting Numeric Print Output
Beyond Basic Arithmetic
Summary of Numbers
Questions and Exercises
Characters
Strings
Converting Between Numbers and Strings
Manipulating Characters in a String
Comparing Strings and Portions of Strings
The StringBuilder Class
Summary of Characters and Strings
Questions and Exercises
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Summary of Characters and Strings

> Most of the time, if you are using a single character value, you will use the primitive `char` type. There are times, however, when you need to use a char as an object—for example, as a method argument where an object is expected. The Java programming language provides a wrapper class that "wraps" the `char` in a `Character` object for this purpose. An object of type `Character` contains a single field whose type is `char`. This `Character` class also offers a number of useful class (i.e., static) methods for manipulating characters.

> Strings are a sequence of characters and are widely used in Java programming. In the Java programming language, strings are objects. The `String` class has over 60 methods and 13 constructors.

> Most commonly, you create a string with a statement like

> >     String s = "Hello world!";

> rather than using one of the `String` constructors.

> The `String` class has many methods to find and retrieve substrings; these can then be easily reassembled into new strings using the `+` concatenation operator.

> The `String` class also includes a number of utility methods, among them `split()`, `toLowerCase()`, `toUpperCase()`, and `valueOf()`. The latter method is indispensable in converting user input strings to numbers. The `Number` subclasses also have methods for converting strings to numbers and vice versa.

> In addition to the `String` class, there is also a `StringBuilder` class. Working with `StringBuilder` objects can sometimes be more efficient than working with strings. The `StringBuilder` class offers a few methods that can be useful for strings, among them `reverse()`. In general, however, the `String` class has a wider variety of methods.

> A string can be converted to a string builder using a `StringBuilder` constructor. A string builder can be converted to a string with the `toString()` method.

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