Conditional Execution - Building Java Programs: A Back to Basics Approach - page 254

Table 4.4 Differences between char and String

char String

Type of value primitive object

Memory usage 2 bytes depends on length

Methods none

length , toUpperCase , . . .

Number of letters exactly 1 0 to many

Surrounded by apostrophes: 'c' quotes: "Str"

Comparing

< , >= , == , . . .

equals

It is also legal to create a char value that represents an escape sequence:

char newline = '\n';

In the previous chapter we discussed String objects. The distinction between
char and String is a subtle one that confuses many new Java programmers. The
main difference is that a String is an object, but a char is a primitive value. A char
occupies a very small amount of memory, but it has no methods. Table 4.4 summa-
rizes several of the differences between the types.
Why does Java have two types for such similar data? The char type exists primar-
ily for historical reasons; it dates back to older languages such as C that influenced
the design of Java.
So why would a person ever use the char type when String is available? It's
often necessary to use char because some methods in Java's API use it as a parame-
ter or return type. But there are also a few cases in which using char can be more
useful or simpler than using String .
The characters of a String are stored inside the object as values of type char .
You can access the individual characters through the object's charAt method, which
accepts an integer index as a parameter and returns the character at that index. We
often loop over a string to examine or change its characters. For example, the follow-
ing method prints each character of a string on its own line:

public static void printVertical(String message) {
for (int i = 0; i < message.length(); i++) {
char ch = message.charAt(i);
System.out.println(ch);

}

}

char versus int
Values of type char are stored internally as 16-bit integers. A standard encoding
scheme called Unicode determines which integer value represents each character.
(Unicode will be covered in more detail later in this chapter.) Since characters are