Specification for JEP 355: Text Blocks (Preview)

The opening delimiter is a sequence of three double quote characters (""") followed by zero or more white spaces followed by a line terminator.

The closing delimiter is a sequence of three double quote characters.

The content of a text block is the sequence of characters that begins immediately after the line terminator of the opening delimiter, and ends immediately before the first double quote of the closing delimiter.

Unlike in a string literal, it is not a compile-time error for a line terminator to appear in the content of a text block.

Example 3.10.6-1. Text Blocks

When multi-line strings are desired, a text block is usually more readable than a concatenation of string literals. For example, compare these alternative representations of a snippet of HTML:

String html = "<html>\n" +
              "    <body>\n" +
              "        <p>Hello, world</p>\n" +
              "    </body>\n" +
              "</html>\n";

String html = """
              <html>
                  <body>
                      <p>Hello, world</p>
                  </body>
              </html>
              """;

Here are some examples of text blocks:

String season = """
                winter
                """;     // the six characters w i n t e r

String greeting = 
    """
    Hi, "Bob"
    """;        // the nine characters H i , SP " B o b "

String salutation =
    """
    Hi,
     "Bob"
    """;        // the ten characters H i , LF SP " B o b "

String empty = """
               """;      // the empty string (zero length)

String quote = """
               "
               """;      // a string containing " alone

String backslash = """
                   \\
                   """;  // a string containing \ alone

The use of the escape sequences \" and \n is permitted in a text block, but not necessary or recommended. However, representing the sequence """ in a text block requires the escaping of at least one " character, to avoid mimicking the closing delimiter.

Example 3.10.6-2. Escape sequences in text blocks

The following snippet of text would be less readable if the " characters were escaped:

String story = """
    "When I use a word," Humpty Dumpty said,
    in rather a scornful tone, "it means just what I
    choose it to mean - neither more nor less."
    "The question is," said Alice, "whether you
    can make words mean so many different things."
    "The question is," said Humpty Dumpty,
    "which is to be master - that's all."""";

If a text block is to denote another text block, then it is recommended to escape the first " of the embedded opening and closing delimiters:

String code = 
    """
    String text = \"""
        A text block inside a text block
    \""";
    """;

The string represented by a text block is not the literal sequence of characters in the content. Instead, the string represented by a text block is the result of processing the content, as follows:

Line terminators are normalized to the ASCII LF character, as follows:
1. An ASCII CR character followed by an ASCII LF character is translated to an ASCII LF character.
2. An ASCII CR character is translated to an ASCII LF character.
Incidental white space is removed, as if by execution of String::stripIndent on the characters in the content.
Escape sequences are interpreted, as in a string literal.

Example 3.10.6-3. Order of content processing

Interpreting escape sequences last allows developers to use \n, \f, and \r for vertical formatting of a string without affecting the normalization of line terminators, and to use \b and \t for horizontal formatting of a string without affecting the removal of incidental white space. For example, consider this text block that mentions the escape sequence \r (CR):

String html = """
              <html>\r
                  <body>\r
                      <p>Hello, world</p>\r
                  </body>\r
              </html>\r
              """;

The \r escapes are not interpreted until after the line terminators have been normalized to LF. Using Unicode escapes to visualize LF (\u000A) and CR (\u000D), and using | to visualize the left margin, the final result is:

|<html>\u000D\u000A
|    <body>\u000D\u000A
|        <p>Hello, world</p>\u000D\u000A
|    </body>\u000D\u000A
|</html>\u000D\u000A

When this specification says that a text block contains a particular character or sequence of characters, or that a particular character or sequence of characters is in a text block, it means that the string represented by the text block (as opposed to the content of the text block) contains the character or sequence of characters.

A text block is always of type String (4.3.3).

At run time, a text block is evaluated to a reference to an instance of type String that corresponds to the string represented by the text block. The string represented by a text block is interned in the same manner the string represented by a string literal.

Example 3.10.6-4. Text blocks represent strings

Text blocks can be used wherever an expression of type String is allowed, such as in string concatenation (15.18.1), in method invocation on class String, and in annotations with String elements:

System.out.println("abc" + """
                           cde
                           """);

String math = """
              1+1 equals
              """ + " " + String.valueOf(2);

String cde = """
             abcde""".substring(2);

@Precondition("""
    rate > 0 &&
    rate <= MAX_REFRESH_RATE
""")
public void setRefreshRate(int rate) { ... }

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Specification for JEP 355: Text Blocks (Preview)

3.10 Literals

3.10.6 Text Blocks

Miscellaneous changes