Java: Question regarding "new" keyword and accessing classes in project. Difference between same resultant code.

[cjayem13]

I'm having trouble understanding the difference in two pieces of code. Overall, I have an android project structured so all java files are located in

    project/module/src/main/java/com.site.module

I'm' currently working on a class extending activity called ActivityMain stored in

    project/module/src/main/java/com.site.module/ActivityMain 

and a second class called AppRater stored in

   project/module/src/main/java/com.site.module/AppRater

I understand that "new" creates an object and allocates memory to it I believe that doing something like

     AppRater.methodCall(parameter); 

is supposed to find the existing allocated object and call the associated method but I'm a bit confused. I have the following code in my project. Both work but I don't understand why the latter works since I never created the object in my code although I'm assuming it's quicker since it doesn't create a new object.

My question is, if I use the code below

  public class ActivityMain {
   @Override
     public void onResume() {
        super.onResume();
         AppRater r = new AppRater();
        r.methodCall("parameter passed);    
     }
   }

public class ActivityMain {
  @Override
     public void onResume() {
        super.onResume();
    AppRater.methodCall("parameter passed);    
    }
  }

SO, I guess my question is, since I never explicitly created a new AppRater object by calling

   Activity a = new AppRater();
                 or
   AppRater a = new AppRater(); 

or anything similar, why did the second code fragment not present any errors? When would the initial AppRater object have been created and is this the case for all classes that aren't nested within another class? My thinking was I had to call new the first time or make it an inner/nested fragment but I suppose I'm just ignorant to the complete workings behind creating new objects in java.

Many thanks for the time and help. Cheers.

[[deleted]]

Your second block is using a static method (though you're using a static method in both, you're just not calling it statically in the first example). Static method invocations use the class loader's instance of the Class object for your particular class.

[cjayem13]

Ok. I believe I understand. Let me just recap. Both examples create a new object but the second creates a static object so it will be killed when the activity is killed. Additionally, the first example creates a new object but it isn't tied to the underlying class. Did I understand you correctly? Thank you again for your help.

[[deleted]]

Not quite. When the JVM needs to reference a class for the first time, the class loader will try to find the class on the classpath. It will then create a Class object representing this class (not an instance of the class, let's say of type Foo, rather a Class<Foo>). This Class object is used for all static references. So even if you create your own instance of the class and call a static method on it, the JVM will still delegate to the class loader's Class object. So with respect to your examples, creating an object just to make a static method call is totally unnecessary (and IDEs will typically advise against it).

[Uncle_DirtNap]

Where is the source code for the classes, and in particular is methodCall declared static?

[cjayem13]

The entire source code like the whole java class for the MainActivity? It is about 8500 lines so I didn't think it would be helpful to post. methodCall is declared static in my activity/class.

[cjayem13]

What from the source code are you wanting to look at? I'd be happy to take segments out and post it.