DeferObservable.java

public class DeferClass {  
  private String value;

  public void setValue(String value) {
    this.value = value;
  }

/*  
 * DeferClass instance = new DeferClass();  
 * Observable<String> value = instance.valueObservable();  
 * instance.setValue("Test Value");  
 * value.subscribe(System.out::println); //null will be printed
 * 
 * Suppose we call the below class and create an Observable,
 * when we call print, it will print null, since value had yet 
 * to be initialized when Observable.just() is called.
 */  
  public Observable<String> valueObservable() {
    return Observable.just(value);
  }
}


public class DeferClass {  
  private String value;

  public void setValue(String value) {
    this.value = value;
  }

/*   
 * Now if we wrap the code inside
 * Observable.defer(), none of the code inside of defer() 
 * is executed until subscription.
 */  
  public Observable<String> valueObservable() {  
    return Observable.defer(() -> Observable.just(value));
  }
}