CODEWITHSUNDEEP
javaobject
Involute
Involute

Reputation: 245

Java: how to get an object to refer to the object it was instantiated in

I am still quite inexperienced with using Java, and would like to solve this stumbling block:

I have created two classes to be used in a rigid body dynamics simulation, called:

RigidBody RigidBodyElement

The plan is to create a RigidBody object. This object will be comprised of many little RigidBodyElement objects. So, inside RigidBody, there will be a single array of type RigidBodyElements to contain all of the rigid body elements.

As for RigidBodyElement, there will be a field variable containing the coordinates of the element relative to a fixed point on the RigidBody object. This variable will be called relativeCoordinates.

That much is fine. The problem arises when we want to find the absolute coordinates of each element, absoluteCoordinates. To find that, we would need to add the rotated relativeCoordinates of RigidBodyElement to the coordinates of the overall rigid body, RigidBody. i.e. writing a function in RigidBodyElement, such that when an instance of RigidBodyElements calls this function, it will get some of the information from the instance of the class RigidBody in which this element is instantiated.

I currently have no idea how to define a function for an object to refer to another object that has instantiated the first object.

Upvotes: 0

Views: 54

Answers (2)

satnam
satnam

Reputation: 11484

another approach is that you could make RigidBodyElement an Inner class.

public class RigidBody{

  private double x, y;
  private List<RigidBodyElement> elements = new ArrayList<>();

  public RigidBody(){
    elements.add(new RigidBodyElement(50,20));
  }

  public class RigidBodyElement(){
    private double x, y;
    public RigidBodyElement(double x, double y){
      this.x=x;
      this.y=y;
    }

    public double getAbsoluteX(){
      //RigidBody.this references the RigidBody which created this element
      return RigidBody.this.x + this.x;
    }
  }
}

Upvotes: 3

wvdz
wvdz

Reputation: 16651

You can use the this keyword.

So you should have a constructor like this:

RigidBodyElement(RigidBody body)
{
    ....
}

And instantiate it like this in an instance method of RigidBody:

new RigidBodyElement(this);

Upvotes: 3

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