The JLS section on unreachable code explains the rationale. Essentially, Java normally shouldn’t use conditional compilation like C routinely does with #ifdef, but there are some situations (such as debugging, and in particular backward binary compatibility) where allowing the compiler to entirely strip out code is needed, and so the specific construct if(false) is permitted … Read more
Static analysis can only do so much, and it will only mark code as unreachable if it can prove that a value cannot be changed. In your code, what happens inside Bar is out of the scope of the method flow and can’t be statically reasoned about. What if Bar‘s constructor launches a thread that … Read more
The first does not compile (you got an error), the second compiles (you just got a warning). That’s the difference. As to why Eclipse detects dead code, well, that’s just the convenience of an integrated development tool with a built-in compiler which can be finetuned more as opposed to JDK to detect this kind of … Read more
The behaviour is defined in the JLS description of unreachable statements: The then-statement is reachable iff the if-then statement is reachable. So the compiler determines that the then-statement (break;) is reachable, regardless of the condition in the if. And a bit further, emphasis mine: A basic for statement can complete normally iff at least one … Read more
From JLS 14.21. Unreachable Statements It is a compile-time error if a statement cannot be executed because it is unreachable. and The else-statement is reachable iff the if-then-else statement is reachable. Your if-then-else statement is reachable. So, by the definition the compiler thinks that the else-statement is reachable. Note: Interestingly the following code also compiles … Read more
Does the existence of such a statement in a given program mean that the whole program is undefined or that behavior only becomes undefined once control flow hits this statement? Neither. The first condition is too strong and the second is too weak. Object access are sometimes sequenced, but the standard describes the behavior of … Read more
Compiler Warning (level 2) CS0162 Unreachable code detected The compiler detected code that will never be executed. Which is just saying, the Compiler understands enough through Static Analysis that it can’t be reached and completely omits it from the compiled IL (hence your warning). Note : You can prove this fact to your self by … Read more