17.1: Characters

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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 displays the letters of the alphabet:

System.out.print("Roman alphabet: ");
for (char c = 'A'; c <= 'Z'; c++) {
    System.out.print(c);
}
System.out.println();

Java uses Unicode to represent characters, so strings can store text in other alphabets like Cyrillic and Greek, and non-alphabetic languages like Chinese. You can read more about it at http://unicode.org/.

In Unicode, each character is represented by a “code unit”, which you can think of as an integer. The code units for uppercase Greek letters run from 913 to 937, so we can display the Greek alphabet like this:

System.out.print("Greek alphabet: ");
for (int i = 913; i <= 937; i++) {
    System.out.print((char) i);
}
System.out.println();

This example uses a type cast to convert each integer (in the range) to the corresponding character.