Static variable usage in Java - object never changes

Question

I have been assigned an IT project in which we have to program various different GUI's to do various things. We are also using a database. Let's assume we are accessing an "EntityManager" in a class called "Database":

public class GUI1 {

    private Database myDatabase;
    public void setDatabase(Database DB){
        myDatabase = DB;
    }

}
public class GUI2 {

    private Database myDatabase;
    public void setDatabase(Database DB){
        myDatabase = DB;
    }

}
public class GUI3 {

    private Database myDatabase;
    public void setDatabase(Database DB){
        myDatabase = DB;
    }
}
etc...

Lets say I'm in "GUI1" and I want to switch to "GUI3". After initializing "GUI3" I would have to pass "myDatabase" reference to it via the "setDatabase()" method, but if I want to go back to "GUI1", I would have to pass back the database reference again...

By now I have around 15 GUIs and it get's annoying to copy and paste the same code around when I know it could be replaced easily. In this case, wouldn't it be correct to just use a static reference to whatever I want inside the "Database" class instead of passing around the reference between all my "GUI*" classes?

Have you considered making an AbstractGUI base class to contain the shared code? — Kenney
– Kenney, Commented Aug 2, 2015 at 14:13

Mordechai · Accepted Answer · 2015-08-02 15:18:40Z

2

Create a singleton database object, where everybody access the same object:

public class Database {

    private Database(){ // privatize the constructor
        // your code here
    }


    private static Database INSTANCE;
    public static Database getInstance() {
        if(INSTANCE == null) {
            // let's make it thread-safe
            synchronized(Database.class) {
                if(INSTANCE == null) // may have changed in the mean while
                                     // by other thread
                    INSTANCE = new Database();
            }
        }
        return INSTANCE;
    }

}

EDIT: Even better, from a thread-safe perspective is the enum:

public enum Database {

    INSTANCE(); // pair of parenthesis, for constructor

    Database() { // constructor
        // your code here
    }

    public static Database getInstance() {
        return INSTANCE;// initialization controlled by system
    }

    public void someMethod(){
        // even allows you to add custom methods
    }

}

edited Aug 2, 2015 at 15:18

answered Aug 2, 2015 at 14:21

Mordechai

16.5k2 gold badges51 silver badges89 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

charlos Over a year ago

This is exactly what I did first, but then my teacher said it would be incorrect according to OOP principles... I just want to verify, this method would be correct?

Mordechai Over a year ago

I doubt that it breaks OOP. Look Java provided the enum which is really just that. (And even better than my example, in a thread-safe perspective). Think of it, I'm going to edit my post to reflect it.

Mordechai Over a year ago

@Downvotter please comment.

Collectives™ on Stack Overflow

Static variable usage in Java - object never changes

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related