Calling a method of an object from another object inside it

Question

I'm new to java and I want to create a multi-threaded application as I'm gonna describe:

There are two main objects a job and a jobRunner.
jobRunner would be created at the beginning and it would fetch a list of strings describing jobs, then it would create a List of job objects.
each job object has a method to run a series of actions in a separate thread. Using that, the jobRunner would run a bunch of jobs toghether on separate threads
jobRunner has also a method to finilize and report back the job status and so each finished job needs to call back that method in it's parent object

My question is about the final step. How can an object inside another one call a method of it's preceding object? Or is it possible to pass an address of the jobRunner object to the job objects so that they would call the object by that address? Thank you for enlightening me :)

Can you share some code? It's kind of hard to follow a question presented like this. — Mureinik
– Mureinik, Commented Oct 29, 2016 at 12:57
I'm still modeling the application and I want to see if this methodology works and I'm on the correct line. The problem is that this problem is not actually related to inheritance but however I searched I got to questions related to inheritance — Mortie
– Mortie, Commented Oct 29, 2016 at 13:01

MikeJ · Accepted Answer · 2016-10-31 21:28:58Z

2

Two options. 1) Use a callback (Cleaner approach) 2) Pass in a reference JobRunner as a parameter to Job (quick approach)

Callback example Declare an interface and define a method to be called at various points in the jobs lifecycle, e.g. void finished()

JobRunner can implement the interface, and passes this to Job. When job is done it can invoke the callback method.

Simple Callback example

public interface JobUpdate {
  void jobCompleted();
}

public JobRunner implements JobUpdate {
   @override
   public void jobCompleted() {
     // Our implemented callback method, called from Job
   }
}

public Job() {
  private JobUpdate update;

  public Job(JobUpdate update) {
    this.update = update;
  }

  public void runJob() {
    // at correct point, invoke the appropriate callback method
    jobUpdate.jobCompleted();
  }
}

edited Oct 31, 2016 at 21:28

answered Oct 29, 2016 at 13:09

MikeJ

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3 Comments

Mortie Over a year ago

Could you explain the second approach too? In both ways we are passing some kind of a reference of the jobRunner object to the job objects, right?

MikeJ Over a year ago

Yes, In 2 you are using a standard callback method (also see Observer pattern)

Mortie Over a year ago

Looks like it was simpler than I thought, As Java passes objects by reference as function arguments by default.

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