LEXICAL STRUCTURE

String Literals

3.10.5

3.10.5   String Literals

A

string literal

 consists of zero or more characters enclosed in double quotes.

Each character may be represented by an escape sequence.

A string literal is always of type

String

 ( 4.3.3,  20.12). A string literal

always refers to the same instance ( 4.3.1) of class

String

.

StringLiteral:

"

StringCharacters

opt

 "

StringCharacters:

StringCharacter

StringCharacters StringCharacter

StringCharacter:

InputCharacter

 but not

"

 or

\

EscapeSequence

The escape sequences are described in  3.10.6.

As specified in  3.4, neither of the characters

CR

 and

LF

 is ever considered to

be an

InputCharacter

; each is recognized as constituting a

LineTerminator

.

It is a compile time error for a line terminator to appear after the opening

"

and before the closing matching

"

. A long string literal can always be broken up

into shorter pieces and written as a (possibly parenthesized) expression using the

string concatenation operator

+

 ( 15.17.1).

The following are examples of string literals:

""

//

the empty string

"\""

//

a string containing

 "

alone

"This is a string"

//

a string containing 16 characters

"This is a " +

//

actually a string valued constant expression,

"two line string"

//

formed from two string literals

Because Unicode escapes are processed very early, it is not correct to write

"\u000a"

 for a string literal containing a single linefeed (

LF

); the Unicode escape

\u000a

 is transformed into an actual linefeed in translation step 1 ( 3.3) and the

linefeed becomes a

LineTerminator

 in step 2 ( 3.4), and so the string literal is not

valid in step 3. Instead, one should write

"\n"

 ( 3.10.6). Similarly, it is not correct

to write

"\u000d"

 for a string literal containing a single carriage return (

CR

).

Instead use

"\r"

.

Each string literal is a reference ( 4.3) to an instance ( 4.3.1,  12.5) of class

String

 ( 4.3.3,  20.12).

String

 objects have a constant value. String literals 

or, more generally, strings that are the values of constant expressions ( 15.27) 

are  interned  so as to share unique instances, using the method

String.intern

( 20.12.47).

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