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# Final

* final fields or variables cannot bereassigned
  * Used to create constants
  * or fields that can only be defined via constructors at the time of object instantiation
  * As the reference is stored in the field/variable, it's object graph (internal fields) can be accessed
    * thus they can be change if the fields of the original field is mutable (ie via public field or getter)
  * This does not mean that the fields are immutable
  * Part of making class immutable if fields are final
    * but must make sure that the object graph is also immutable
  * any final field must be initialized before the constructor completes.
    * static final fields, this means that we can initialize them:
      * upon declaration as shown in the above example
      * in the static initializer block
    * For instance final fields, this means that we can initialize them:
      * upon declaration
      * in the instance initializer block
      * in the constructor
* Final arguments can’t be changed inside a method
* final methods cannot be overriden by subclasses
  * you’d mark a method as final when you’re defining a parent class and want to guarantee certain behavior of a method in the parent class, regardless of which child is invoking the method.
* final classes cannot be subclassed/extended
  * prevents a user extending a class and replacing it with a subclass which might give access to private state or non private behaviour, which could be used during runtime.
* What’s the difference between making all methods of the class final and marking the class itself final?
  * In the first case, we can extend the class and add new methods to it.
  * In the second case, we can’t do this.
* Good practice to use final everywhere
  * Depends, as it can lead to a lot of verbose code
  * As long as you code with the convention of all method param, local variables as final

## Links

* <https://www.baeldung.com/java-final>
* <https://www.geeksforgeeks.org/final-keyword-java/>