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 (that is, 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.