Observe any object variable value change with RxJava2 PublishSubject wrapper written in Java

Variable.java

package net.cargo.reactive;

import android.support.annotation.Nullable;
import io.reactivex.Observable;
import io.reactivex.subjects.PublishSubject;

import static net.cargo.application.Cargo.check;

/**
 *  Usage:
 *
 *  final T initialValue = 0; // T - any object type
 *
 *  Variable<T> myValue = new Variable(initialValue);
 *
 *  myValue
 *    .subject()
 *    .subscribe(otherValue ->
 *               changeValue(otherValue));
 *
 *  myValue.set(1);
 *  myValue.set(2);
 *  myValue.set(3);
 *
 *  final T lastValue = myValue.get(); // lastValue = 3
 *
 **/

public class
Variable<T>
{
  // fields
  PublishSubject<Variable<T>> subject;
  T                           value;
  
  public
  Variable(){}
  
  public 
  Variable(@Nullable final
           T value)
  {
    if(check(value,
             "value in " +
             "Variable.constructor"))
    {
      subject =
      PublishSubject.create();
      
      set(value);
    }
  }
  
  public final void
  set(@Nullable final
      T value)
  {
    if(check(value,
             "value in " +
             "Variable.set"))
    {
      this.value = value;
    }
    
    subject =
    initializeVariableObservable(subject);
    
    if(check(subject,
             "subject in " +
             "Variable.set"))
    { 
      subject
      .onNext(this);
    }
  }
  
  @Nullable
  public final T
  get()
  {
    T result = null;
    
    if(check(value,
             "value in " +
             "Variable.get"))
    {
      result = value;
    }
    return result;
  }
  
  @Nullable
  public final Observable<Variable<T>>
  subject()
  {
    Observable<Variable<T>> result = null;
  
    subject =
    initializeVariableObservable(subject);
    
    if(check(subject,
             "subject in " +
             "Variable.subject"))
    {
      result = subject;
    }
    return result;
  }
  
  @Nullable
  private PublishSubject<Variable<T>>
  initializeVariableObservable(@Nullable final
                               PublishSubject<Variable<T>> subject)
  {
    PublishSubject<Variable<T>> result = null;
    
    final PublishSubject<Variable<T>>
    variablePublishSubject =
    (subject == null)
    ? PublishSubject.create()
    : subject;
    
    if(check(variablePublishSubject,
             "variablePublishSubject in " +
             "Variable.initializeVariableObservable"))
    {
      result = variablePublishSubject;
    }
    return result;
  }
}