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Many classes allow inclusion of escape sequences in character and string literals; examples include {{Pattern}} as well as classes that support {{XML}}- and {{SQL}} -based actions by passing {{String}}string arguments to methods. According to the Java Language Specification \[[JLS 2005|AA. References#JLS 05]\], Section 3.10.6, "Escape Sequences for Character and String Literals" |
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Correct use of escape sequences in String string literals depends on correct understanding of how the escape sequences are interpreted. SQL statements written in Java, for example, sometimes require certain escape characters or sequences (e.g., sequences containing \t, \n, \r). When representing SQL queries in Java String string form, all escape sequences must be preceded by an extra backslash for correct interpretation.
As another example, consider the Pattern class used in performing regular expression-related tasks. A String string literal used for pattern matching is compiled into an instance of the Pattern type. When the pattern to be matched contains a sequence of characters that is identical to one of the Java escape sequences — '\' 'n' "\" and "n", for example — the Java compiler will treat treats that portion of the string as a Java escape sequence , and will consequently transform transforms the sequence into a newline character. ConsequentlyTo avoid inserting a newline character, the programmer must precede the "\n" sequence with an additional backslash to prevent the Java compiler from treating it as an escape sequence. The string constructed from the resulting sequence
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'"\\n'" |
consequently contains the correct two-character sequence '\' 'n' and correctly denotes back references rather than a newline.
In general, for a particular escape character of the form '\X', the equivalent Java representation is:
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"\\X" |
Noncompliant Code Example
This noncompliant code example defines a method, splitWords(), that finds matches between the String string literal and the input sequence. The programmer believes that String string literals can be used as is for regular expression patterns . Consequently, he and consequently initializes the string WORDS to "\b", expecting that the string literal will hold the escape sequence for matching a word boundary. However, the Java compiler treats the "\b" as a Java escape sequence, and the string WORDS silently compiles to a backspace character.
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This compliant solution shows the correctly escaped value of the String string literal WORDS that results in a regular expression designed to split on word boundaries.
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Incorrect use of escape characters in String string literals can result in misinterpretation and potential corruption of data.
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