Initialize a static final field in the constructor

Question

public class A  {         private static final int x;      public A()      {         x = 5;     } } 

• final means the variable can only be assigned once (in the constructor).
• static means it's a class instance.

I can't see why this is prohibited. Where do those keywords interfere with each other?

Answer 1

A constructor will be called each time an instance of the class is created. Thus, the above code means that the value of x will be re-initialized each time an instance is created. But because the variable is declared final (and static), you can only do this

class A {         private static final int x;      static {         x = 5;     } } 

But, if you remove static, you are allowed to do this:

class A {         private final int x;      public A() {         x = 5;     } } 

OR this:

class A {         private final int x;      {         x = 5;     } } 

Answer 2

static final variables are initialized when the class is loaded. The constructor may be called much later, or not at all. Also, the constructor will be called multiple times (with each new object ), so the field could no longer be final.

If you need custom logic to initialize your static final field, put that in a static block