Singleton

[oll3i]

public class Cennik {
     private static Cennik instance = null;
 
       private Cennik() {  // prywatny konstruktor
       }
 
       public static Cennik getInstance() {
          if(instance == null) {
             instance = new Cennik();
          }
          return instance;
       }
 
}
 
 
public class Kwiaciarnia {
  Cennik c= Cennik.getInstance();
}
 

but eclipse highlights getInstance(); and says the method getInstance() is undefined for type Cennik

[sicarie]

public class Cennik {
     private static Cennik instance = null;
 
       private Cennik() {  // prywatny konstruktor
       }
 
       public static Cennik getInstance() {
          if(instance == null) {
             instance = new Cennik();
          }
          return instance;
       }
 
}
 
 
public class Kwiaciarnia {
  Cennik c= Cennik.getInstance();
}
 

but eclipse highlights getInstance(); and says the method getInstance() is undefined for type Cennik

I don't think you want to set your declaration of instance to null (private static Cennik instance = null; ). Other than that, I think that the only other thing you're missing is the copy constructor - someone with malicious intentions can overload the default copy constructor and create a copy of a singleton object, having two at the same time, you want to have something like

clone() throws CloneNotSupportedException {
    throw new CloneNotSupportedException;
}
 

[oll3i]

sorry but where

[sicarie]

sorry but where

Just as a method in your Cennik class.

[RedSon]

Since instance is static doesn't that mean that it cannot get a "new" object during runtime. I thought the point of static ment that it cannot be changed except at build time.

[sicarie]

Since instance is static doesn't that mean that it cannot get a "new" object during runtime. I thought the point of static ment that it cannot be changed except at build time.

Honestly, I have no idea. I learned 'static' when I was programming in C++, and it's completely different in Java (I thought it had something to do with access, but I gave up on trying to get the finer points of Java like the meaning of static and how Java does memory management.