is it possible to access an instance of a non static class from another class

Question

lets say I have classA and classB.

I know that I cannot just call a non static variable or method of classA from classB because the system doesn't know which instance of classA I want to use. but is there a way to specify which instance?

something like this: in class A I declare a static variable which whould hold the some sort of ID or context to the specific instance of the class

class classA{ static Instance instance onCreate(){ instance = thisInstance(); } Method1(){ } }

then in class B I would refer to that instance like this:

 ClassA.instance.method1();

is something like this possible? if so, what is the exact syntax?

[Bonus]: if no, what is the simplest way invoke a method in a class from another class? I assume some sort of event handling would be required. (I come from the embedded c world)

Get a reference to the other object and call a method on it? You might want to take a step back and go over some Java basics. — Dave Newton
– Dave Newton, Commented Sep 21, 2013 at 2:12

cmd · Accepted Answer · 2013-09-21 02:32:55Z

1

Declare a static member in ClassA

public class ClassA { public static ClassA object = new ClassA(); public void doStuff() { // do stuff } }

Then in ClassB

public void someMethod() { ClassA.object.doStuff(); }

edited Sep 21, 2013 at 2:32

answered Sep 21, 2013 at 2:14

cmd

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3 Comments

Siavash Over a year ago

No this not what I'm trying to do, I want to call a method in classA thats defined in classA, not a built in method such as toString.

Siavash Over a year ago

this wouldn't work either, I want reference to the classA that was created by launching the app, not any arbitrary copy of classA. ClassA in my case is my main activity.

cmd Over a year ago

ClassA.object is a static variable. Static variables are initialized only once, at the start of the execution. It is a single copy to be shared by all instances of the class. You could make a private constructor in ClassA to ensure, ClassA.object is the only instance of ClassA in your app.

Josh Crozier · Accepted Answer · 2013-11-02 23:07:06Z

In class B, you can define:

Class B { private static ClassA instanceA = null; // By making it null, you can later confirm that the instance was successfully passed by making sure instanceA != null. /** * This method allows you to pass the instance of ClassA into B so you can use its non-static methods. */ public static void setInstanceA(ClassA instance) { instanceA = instance; } }

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