The final keyword in Java

Semantics of 1.final:

The semantics of the final modifier in Java are: immutable.

In Java, final can be decorated with: variables, methods, and classes. The variable is immutable, the method cannot be overridden, and the class is not inheritable.

2. Final modifier variables:

When final modifies a member variable, the timing of the initialization is different when the class variable and the instance variable are decorated.

An instance variable can assign an initial value at declaration time, initialization block, constructor;

A class variable can only be initialized in a static initialization block at declaration time.

3. Macro substitution:

The semantics and constants of the final variable are very similar.

However, in some cases, the final variable is replaced with a "constant" at compile time. That is, at compile time, we are able to directly determine the value of the final variable. Even if the value of the final variable is certain constants are obtained by simple operations, it is also possible.

4. Closures (inner Class)

References to other variables in the inner class must be final decorated. Because, we want to make sure that the closure can exist from the life cycle of the main class. Then this requires that these external variables referenced must be constants.

The final keyword in Java