Why does javac insert Objects.requireNonNull(this) for final fields?
Since the field is not only final
, but a compile-time constant, it will not get accessed when being read, but the read gets replaced by the constant value itself, the iconst_5
instruction in your case.
But the behavior of throwing a NullPointerException
when dereferencing null
, which would be implied when using a getfield
instruction, must be retained¹. So when you change the method to
int sumA() { Temp t = this; return 1 + t.field;}
Eclipse will insert an explicit null check too.
So what we see here, is javac
failing to recognize that in this specific case, when the reference is this
, the non-null property is guaranteed by the JVM and hence, the explicit null check is not necessary.
¹ see JLS §15.11.1. Field Access Using a Primary:
If the field is not
static
:
- The Primary expression is evaluated. If evaluation of the Primary expression completes abruptly, the field access expression completes abruptly for the same reason.
- If the value of the Primary is
null
, then aNullPointerException
is thrown.- If the field is a non-blank
final
, then the result is the value of the named member field in typeT
found in the object referenced by the value of the Primary.…