Some help

[horvath.alexandru]

Hello.

I have the following singleton:

public class Singleton {


private static final Singleton singleton = new Singleton();

private ArrayList<String> list = new ArrayList<String>();

private Singleton() {
}

public static Singleton getInstance() {
return singleton;
}


// ..... and some public methods to access "list";


}

..... and i have the following class:


public class Usage {

private final Singleton singletonInstance =
Singleton.getInstance();

}



My question is: it is ok that in Usage class the singletonInstance is
declared final? can i still add/delete from the list declared in the
Singleton? Why?

Thank you in advance

 

[Matt Humphrey]

Hello.

I have the following singleton:

public class Singleton {


private static final Singleton singleton = new Singleton();

private ArrayList<String> list = new ArrayList<String>();

private Singleton() {
}

public static Singleton getInstance() {
return singleton;
}


// ..... and some public methods to access "list";


}

.... and i have the following class:


public class Usage {

private final Singleton singletonInstance =
Singleton.getInstance();

}



My question is: it is ok that in Usage class the singletonInstance is
declared final? can i still add/delete from the list declared in the
Singleton? Why?

The final applies to the reference to the Singleton instance, not to its
contents. It simply prevents you from changing to a different Singleton
instance.

Matt Humphrey (e-mail address removed) http://www.iviz.com/

 

[horvath.alexandru]

I understand now .
I'm new to Java so i am sorry if my question was a little silly.
Thank you for your quick response.

 

[Jinkx]

It was not at all silly., it was a very good question . Even i had
little idea about that...

 

[Roedy Green]

private final Singleton singletonInstance =
Singleton.getInstance();

}



My question is: it is ok that in Usage class the singletonInstance is
declared final? can i still add/delete from the list declared in the
Singleton? Why?

Why would final not be ok? You don't change the value anywhere do you?

Final is not C++ const. It simply means the reference to the object is
frozen. It says nothing about changing the value of fields in the
object. It says there is one object for all time.