Classier Puzzlers - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 202

Solution 68: Shades of Gray
There is no obvious way to decide whether this program should print Black or White . The compiler
generally rejects ambiguous programs, and this one certainly appears ambiguous. Therefore, it
seems only natural that it should be illegal. If you tried it, you found that it is legal and prints White .
How could you possibly have known?
It turns out that there is a rule that governs program behavior under these circumstances. When a
variable and a type have the same name and both are in scope, the variable name takes
precedence [JLS 6.5.2]. The variable name is said to obscure the type name [JLS 6.3.2]. Similarly,
variable and type names can obscure package names. This rule is indeed obscure, and any
program that depends on it is likely to confuse its readers.
Fortunately, programs that obey the standard Java naming conventions almost never
encounter this issue. Classes begin with a capital letter and are written in MixedCase , variables
begin with a lowercase letter and are written in mixedCase , and constants begin with a capital letter
and are written in ALL_CAPS . Single capital letters are used only for type parameters, as in the
generic interface Map<K, V> . Package names are written in lower.case [JLS 6.8].
To avoid conflict between constant names and class names, treat acronyms as ordinary words in
class names [EJ Item 38]. For example, a class representing a universally unique identifier should
be named Uuid rather than UUID , even though the acronym is typically written UUID. (The Java
platform libraries violate this advice with such class names as UUID , URL , and URI .) To avoid
conflicts between variable names and package names, don't use a top-level package or domain
name as a variable name. Specifically, don't name a variable com , org , net , edu , java , or javax .
To remove all ambiguity from the ShadesOfGray program, simply rewrite it to obey the naming
conventions. It is clear that the following program prints Black . As an added bonus, it sounds the
same as the original program when read aloud.
public class ShadesOfGray {
public static void main(String[] args){
System.out.println(Ex.Why.z);
}
}
class Ex {