Question

Which part of the following class code is invalid?

class MooCow
{ int x = 3;
int y = x + 1; }
a class MooCow
b int x = 3;
c int y = x + 1;
d no part; the code is valid

Answer 1

The code provided does not contain any invalid parts as variables are declared and initialized in order. Even though 'int y = x + 1;' references another variable, it is done after 'x' has been initialized, which is allowed.

Step-by-step explanation:

The part of the class code that is invalid is c int y = x + 1;. In Java, instance variables can be initialized using constant expressions or with expressions that include references to other instance variables. However, the order of initialization follows the order in which the variables are declared. In this case, because 'y' is being initialized with the reference to 'x', which has already been initialized, there should be no issues as 'x' is declared before 'y'.

However, this might not be the case in some programming scenarios where the compiler does not permit references to variables that are declared later. To avoid potential errors, it is generally safe to only use constant expressions for field initializers or to use a constructor or an initialization block to set the values of variables using expressions that involve other variables.