Puzzlers with Character - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 37

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Puzzle 15: Hello Whirled

The following program is a minor variation on an old chestnut. What does it print?

/**

* Generated by the IBM IDL-to-Java compiler, version 1.0

* from F:\TestRoot\apps\a1\units\include\PolicyHome.idl

* Wednesday, June 17, 1998 6:44:40 o'clock AM GMT+00:00

*/

public class Test {

public static void main(String[] args) {

System.out.print("Hell");

System.out.println("o world");

}

}

Solution 15: Hello Whirled

This puzzle looks fairly straightforward. The program contains two statements. The first prints Hell
and the second prints o world on the same line, effectively concatenating the two strings.
Therefore, you might expect the program to print Hello world . You would be sadly mistaken. In
fact, it doesn't compile.

The problem is in the third line of the comment, which contains the characters \units . These
characters begin with a backslash ( \ ) followed by the letter u , which denotes the start of a Unicode
escape. Unfortunately, these characters are not followed by four hexadecimal digits, so the Unicode
escape is ill-formed, and the compiler is required to reject the program. Unicode escapes must be
well formed, even if they appear in comments.

It is legal to place a well-formed Unicode escape in a comment, but there is rarely a reason to do so.
Programmers sometimes use Unicode escapes in Javadoc comments to generate special characters
in the documentation: