Fundamentals of Characters and Strings

Characters are the fundamental building blocks of Java source programs. Every program is composed of a sequence of characters thatwhen grouped together meaningfullyare interpreted by the computer as a series of instructions used to accomplish a task. A program may contain character literals. A character literal is an integer value represented as a character in single quotes. For example, 'z' represents the integer value of z, and ' ' represents the integer value of newline. The value of a character literal is the integer value of the character in the Unicode character set. Appendix B presents the integer equivalents of the characters in the ASCII character set, which is a subset of Unicode (discussed in Appendix F). For detailed information on Unicode, visit www.unicode.org.

Recall from Section 2.2 that a string is a sequence of characters treated as a single unit. A string may include letters, digits and various special characters, such as +, -, *, / and $. A string is an object of class String. String literals (stored in memory as String objects) are written as a sequence of characters in double quotation marks, as in:

	"John Q. Doe"	(a name)
	"9999 Main Street"	(a street address)
	"Waltham, Massachusetts"	(a city and state)
	"[phone]"	(a telephone number)

A string may be assigned to a String reference. The declaration

 String color = "blue";

initializes String reference color to refer to a String object that contains the string "blue".

Performance Tip 29.1

Java treats all string literals with the same contents as a single String object that has many references to it. This conserves memory.