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:

	" StringCharactersopt "

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).

Thus, the test program consisting of the compilation unit (§7.3):


package testPackage;



class Test {
	public static void main(String[] args) {
		String hello = "Hello", lo = "lo";
		System.out.print((hello == "Hello") + " ");
		System.out.print((Other.hello == hello) + " ");
		System.out.print((other.Other.hello == hello) + " ");
		System.out.print((hello == ("Hel"+"lo")) + " ");
		System.out.print((hello == ("Hel"+lo)) + " ");
		System.out.println(hello == ("Hel"+lo).intern());
	}
}

class Other { static String hello = "Hello"; }

and the compilation unit: 


package other;

public class Other { static String hello = "Hello"; }

produces the output: 

true true true true false true

This example illustrates six points: