Ambiguity of the else in if-else statements

Consider the following code fragment:

if (a > 0) if (b > 0) System.out.println("b positive");
else System.out.println("???");

System.out.println("???") could in principle be the else-branch of:

• the first if: hence we should replace "???" with "a negative";
• the second if: hence we should replace "???" with "b negative".

The ambiguity is solved by considering that an else always refers to the nearest if without an associated else. In the above example we have:

if (a > 0)
  if (b > 0)
    System.out.println("b positive");
  else
    System.out.println("b negative");

It is always possible to use a block (i.e., {..}) to disambiguate nested if-else statements. In particular, if we want that an else refers to an if that is not the immediately preceding one, we have to enclose the immediately preceding if in a block. For example:

if (a > 0) {
  if (b > 0)
    System.out.println("b positive");
} else
  System.out.println("a negative");