Write a public
getter but no public
setter. And the field itself private
Class variable: public access read-only, but private access r/w
-
15-01-2022 - |
Pregunta
In my current project I have a class which stores its Instance in a variable. This Instance should be accesible by all other classes in the project, but it may only be altered by its own class.
How can I achieve this?
Solución
Otros consejos
In short that is called immutable object
, state of Object
cannot change after it is constructed.
String
is a common example of immutable Class
.
Make a class
immutable
by following-
- ensure the class cannot be
overridden
- make theclass
final
, or usestatic
factories and keep constructors private. - make fields
private
andfinal
- force callers to construct an object completely in a single step,
instead of using a
no-argument constructor
combined with subsequent calls tosetXXX
methods. - do not provide any methods which can change the state of the object
in any way - not just
setXXX
methods, but any method which can change state - if the class has any mutable object fields, then they must be defensively copied when passed between the class and its caller.
Someone suggests "public getter but no public setter for the private field."
Caution: This would only work if the field is primitive type.
If it is an object with setters, the content can still be modified; thus not read-only.
It will be interesting to see Java language provide some constructs to make a return type read-only without having to do a deep-copy / clone.
i'm imaging like ReadOnly getEmployee() { ...}
The boilerplate code for instantiating a singleton can be found in many places, see for example http://www.javacoffeebreak.com/articles/designpatterns/index.html
Be aware that many consider the singleton to be an antipattern because it's pretty hard to get rid of once your application is littered with references to the singleton.