• a class or method declared final cannot be overridden (this is not a problem, as you favor composition over inheritance, right?) ;

  • a variable declared final can be assigned only once ;

  • method-local classes can access only the final variables declared before the class in the very method

  • โ€ฆโ€‹ check the Java Language Specification, 3rd edition, for the reference information.

Let us see some basic CODE:

short result;
int value = 10;
result = 3*value-7;

Suppose this forms the body of a method, will this compile ?

The answer isโ€ฆโ€‹.. NO! The compiler is nice enough to tell you that such operations, a.k.a. narrowing primitive conversions, may result in a loss of precision. As a matter of fact, you cannot fit the 32 bits of int into the 16 of short.

You still have the option to force the conversion:

short result;
int value = 10;
result = (short) (3*value-7);
 * without the parentheses around, only the literal 3 would be converted to short
 * however, value is of type integer and 3 would be immediately promoted back to integer, nullifying the explicit conversion

โ€ฆ in which case only the n lowest bits (n being the target type size i.e. 16 for short) of the expression result are kept.

So yes, you can force the conversion as a workaround. Here is a slight variation of our first non-compiling piece of code:

short result;
final int value = 10;
result = 3*value-7;

Will this compile ?

This time, the answer is YES!

I guess you are wondering about what is so different between this and the original version ? The fact that a final variable cannot be assigned more than once has an interesting consequence: the variable is a constant, its contents are known at compile time. Therefore, the compiler knows exactly that you are trying to assign to result the result of 3*10-7. It can replace value by the literal.

This process is called compiler inlining.

As a final exercise (no answer provided this time), will the following block compile?

short result;
final int value = 10925;
result = 3*value-7;

Have fun!