Puzzlers with Character - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 35

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Puzzle 14: Escape Rout
The following program uses two Unicode escapes , which represent Unicode characters by their
hexadecimal numeric codes. What does the program print?
public class EscapeRout {
public static void main(String[] args) {
// \u0022 is the Unicode escape for double quote (")
System.out.println("a\u0022.length() + \u0022b".length());
}
}
Solution 14: Escape Rout
A naive analysis of the program suggests that it should print 26 because there are 26 characters
between the quotation marks that bound the string "a\u0022.length() + \u0022b" . A deeper
analysis suggests that the program should print 16 , as each of the two Unicode escapes requires six
characters in the source file but represents only one character in the string. The string is therefore
ten characters shorter than it appears. Running the program tells a different story. It prints neither 26
nor 16 but 2 .
The key to understanding this puzzle is that Java provides no special treatment for Unicode
escapes within string literals. The compiler translates Unicode escapes into the characters they
represent before it parses the program into tokens, such as strings literals [JLS 3.2]. Therefore, the
first Unicode escape in the program closes a one-character string literal ( "a" ), and the second one
opens a one-character string literal ( "b" ). The program prints the value of the expression
"a".length() + "b".length() , or 2 .
If the author of the program had actually wanted this behavior, it would have been much clearer to
say:
System.out.println("a".length() + "b".length());
More likely, the author wanted to put the two double quote characters into the string literal. You
can't do this with Unicode escapes, but you can do it with escape sequences [JLS 3.10.6]. The
escape sequence representing a double quote is a backslash followed by a double quote ( \" ). If the