Think Java

Chapter 9. Strings and Things

In Java and other object-oriented languages, an object is a collection of data that provides a set of methods. For example, Scanner, which we saw in “The Scanner Class”, is an object that provides methods for parsing input. System.out and System.in are also objects.

Strings are objects, too. They contain characters and provide methods for manipulating character data. We explore some of those methods in this chapter.

Not everything in Java is an object: int, double, and boolean are so-called primitive types. We will explain some of the differences between object types and primitive types as we go along.

Characters

Strings provide a method named charAt, which extracts a character. It returns a char, a primitive type that stores an individual character (as opposed to strings of them).

String fruit = "banana";
char letter = fruit.charAt(0);

The argument 0 means that we want the letter at position 0. Like array indexes, string indexes start at 0, so the character assigned to letter is b.

Characters work like the other primitive types we have seen. You can compare them using relational operators:

if (letter == 'a') {
    System.out.println('?');
}

Character literals, like 'a', appear in single quotes. Unlike string literals, which appear in double quotes, character literals can only contain a single character. Escape sequences, like '\t', are legal because they represent a single character.

The increment and decrement operators work with characters. So this loop ...