Java variable scope in if statement [duplicate]

Question

I received a compilation error for the following code:

if(true)     int a = 10; else     int b = 20; 

If I change it to the following code, then there is no compilation error:

if(true) {     int a = 10; } else {     int b = 20; } 

Why is the first syntax wrong, and from what language standard?

Answer 1

The Java specification says that an if-then-else statement is of the following form:

IfThenElseStatement:     if ( Expression ) StatementNoShortIf else Statement 

Where Statement and StatementNoShortIf can be various things including blocks (code surrounded with braces), assignments (to already declared variables), other if statements etc.

Of note is that declaration statements (e.g. int a; or int a = 10;) are missing from that list, thus you get a compilation error.

For the full list, you can read the Java specification here: http://docs.oracle.com/javase/specs/