STRINGS - Introduction to Java Programming - page 336

9.1 Introduction
The classes String , StringBuilder , and StringBuffer are used for processing
strings.

Key
Point

A string is a sequence of characters. Strings are frequently used in programming. In many
languages, strings are treated as an array of characters, but in Java a string is treated as an
object. This chapter introduces the classes for processing strings.

9.2 The String Class
A String object is immutable: Its content cannot be changed once the string is
created.

Key
Point

The String class has 13 constructors and more than 40 methods for manipulating strings.
Not only is it very useful in programming, but it is also a good example for learning classes
and objects.

9.2.1 Constructing a String
You can create a string object from a string literal or from an array of characters. To create a
string from a string literal, use the syntax:

String newString = new String(stringLiteral);

The argument stringLiteral is a sequence of characters enclosed inside double quotes.
The following statement creates a String object message for the string literal "Welcome
to Java" :

String message = new String( "Welcome to Java" );

Java treats a string literal as a String object. Thus, the following statement is valid: string literal object

String message = "Welcome to Java" ;

You can also create a string from an array of characters. For example, the following state-
ments create the string "Good Day" :

char [] charArray = { 'G' , 'o' , 'o' , 'd' , ' ' , 'D' , 'a' , 'y' };
String message = new String(charArray);

Note
A String variable holds a reference to a String object that stores a string value. Strictly
speaking, the terms String variable , String object , and string value are different, but
most of the time the distinctions between them can be ignored. For simplicity, the term
string will often be used to refer to String variable, String object, and string value.

String variable, String
object, string value

9.2.2 Immutable Strings and Interned Strings
A String object is immutable; its contents cannot be changed. Does the following code
change the contents of the string?

immutable

String s = "Java" ;
s = "HTML" ;

The answer is no. The first statement creates a String object with the content "Java" and
assigns its reference to s . The second statement creates a new String object with the content