comparing defer with just usage

deferJustUsage.java

package com.bisapp.rxjavaexamples;

import java.util.concurrent.Callable;

import io.reactivex.Observable;
import io.reactivex.ObservableSource;

public class Book {

    String page = "First page";

    public void setPage(String page) {
        this.page = page;
    }

    public Observable<String> justObservable() {
        return Observable.just(page);
    }

    public Observable<String> deferObservable() {
        return Observable.defer(new Callable<ObservableSource<String>>() {

            @Override
            public ObservableSource<String> call() throws Exception {
                return Observable.just(page);
            }
        });
    }

}

//Calling the example
 private void deferExample(){
        Book newBook = new Book();
        Observable<String> justObservable = newBook.justObservable();
        Observable<String> deferObservable = newBook.deferObservable();
        newBook.setPage("Second Page");

        justObservable.subscribe(s -> {
            //This will print the default value which is First Page
            //Since the just create the observable even before the subscription
            Log.d("RxJava Just",s);
        });
        deferObservable.subscribe(s -> {
            //This will print the default value which is Second Page
            //Since the defer wrapper wait till subscription before creating the observable
            Log.d("RxJava Defer",s);
        });;
    }