How to prevent singleton class from Reflection | serialization | Cloning | Java Techie

[@nandkishorwankhade8012]

You are just amazing as usual, thanks for crisps explanation.😊

[@saumitrasaxena8470]

Hi , First of all congrats for good explanation . I did more deeper analysis into it and can see this code can also break. Let's see how. Suppose we create 2 Threads . Thread-1 calls getInstance() and reaches line 21 , and now 2nd Thread I used reflection code and new Object is created via constructor as instance is still null. And now again when line 21 is executed ,new instance is created again.So two object is created.

[@iltwrrm]

thanks Java Techie. I love your videos and how you enhance our understanding about concepts such as this, creating a Singleton, and then breaking it; really helps our understanding and furthers our comprehension and knowledge. love it. keep ‘em coming

[@parthdalvi5855]

Thank you for sharing this. Its really easy to understand.

[@dineshkumar-lf2vk]

bhai maza hi tumari videos ko dekhne me aata h. Hindi

[@jibandeepbal1639]

Very well explained. Thank you for sharing your knowledge.

[@myakhandbharat-2024]

Very good Information Man 🙂.

[@kumarinidhi90]

wonderful and knowledgeable video.. Really understood the concepts and it is very useful video. I have a request, please make a similar series for JavaScript interview questions and a similar series for react js interview questions ..

[@balajibollu7197]

super thanks bro sharing for knowledge

[@swathiallu9819]

Very good explanation. Its clean and clear. Thanks

[@RAVI_GIT]

Excellent Idea

[@ramanareddysagili3626]

Outstanding man

[@sushilrajiwade3551]

Very Nice Explanation!!! Thank You

[@tulasiramsunkara]

Excellent explanation

[@sumannagella5034]

hi sir thanks for posting very useful videos, please post some other most important concepts of real time and also some more important design patterns. so that it will be helpful for lot of developers

[@Javatechie]

Ok will do it suman

[@nagarajanerode]

Good explanations

[@cvarun9221]

WATCH @ 1.5x speed, save time. Thanks !

[@AmitGadaley17]

Very useful and well explained!!

[@abhrajitnandy]

For reflection case: can we return the same instance instead of throwing exception? Like how in readResolve()

[@Javatechie]

But how can we return from the constructor buddy

[@abhrajitnandy]

@@Javatechie Oh ! My bad.

[@Javatechie]

@abhrajitnandy no problem

[@bhaktilatadash7619]

Nice explanation..Thank u

[@maheshguptatallada6015]

Hi Sir, @Java Techie Could you please clarify the below. when IllegalArgumentException is runTime one, why the compiler is asking us to throw it in compile time in this code ?

[@858Bikash]

Thank you sir🙏🙏

[@greentorainchannel386]

Hello Sir, Thank you for detailed info on Singleton pattern. I have a question Sir, don't we need to add null check in readResolve() method? Could you please help in clarifying this Sir?

[@Javatechie]

No readResolve only called at the time of deserialize so here we want to return the existing instance . that's why no null check required here

[@SanjeevKulkarniWorld]

Good work 👍

[@muttaiahv2328]

could you pease do the video for all other design patterns sir that would help us to understand the importance of various design patterns .

[@Javatechie]

Will do that

[@sameerpatere2983]

Thank you, sir. Nice explanation

[@manjosh1990]

Can you also show how to break it using classloaders and how to avoid it.

[@palaniappanrm6277]

Hi, let's say we export these classes as a jar to other clients. They didn't create any Singleton objects yet. They have a file that has our singleton object serialized. When they read the file and try to deserialize it, this readResolve method will get called and will return instance which is pointing to null. I think we should have a null check in the readResolve method. Right?

[@Javatechie]

You are correct in lazy Singleton approach we should add null check but if it is eager Singleton approach the Then it's not required . Because on class level we are creating instance in eager loading Singleton approach

[@palaniappanrm6277]

@@Javatechie I was pointing to lazy load approach only. Thanks.

[@saumitrasaxena8470]

if I create an object using reflection first -- I will have one object as first-time instance is null so object is created using reflection and 2nd time i call getInstance then I will get object created by reflection ....Am i correct ?

[@maan9011]

Superb

[@chetankhandave1072]

Is it better to make static variable as volatile ?

[@kishorekumar2554]

Thank you

[@preetird8385]

Good explanation. Thank you 👍

[@kishordige4654]

Thanks Man

[@sarikagarg8185]

Can we use transient keyword at declaration place of instance. So that object creation due to serialisation could be avoided

[@Javatechie]

Serialization never create object . Object can be created using deserialization

[@sarikagarg8185]

@@Javatechie but if objects are not mapped in file then how deserialization will do anything ?

[@Javatechie]

Can we perform deserialization from only file ?

[@sarikagarg8185]

@@Javatechie As per the code you shown a serialization is done in a file. I also have a query that once a class is created which don't extends to myclone and don't implements serelizable interface the how some othe program would be able to make clone out of that class

[@Javatechie]

Let's say your singleton class extends from some other class and that class extends from Serializable then in that situation anyone can deserilize your singleton class right ?

[@priyankawagh5217]

Perfect!

[@mohammadmujahid8850]

ultimate.

[@minatimahapatra4182]

hi Sir. I have tried with implementing Cloneable(I) in LazySingleton class and worked fine with breaking Singleton behaviour. So why should we go for MYClone class.

[@Javatechie]

In some worst senario we may need my class to be extends from some other class .so In such case if that class implement Clonable then it will break the rules . So for demonstrate purpose I created this MyClone class

[@saurabhkailashchandrapuran8609]

Basant sir plz make more videos on interview question like circular dependency on beans and many more which you think will be help in interview.

[@Javatechie]

Okay I will

[@rabindrakumar949]

Without throwing exception we should return the same object. With this the applications won't break because of exception.

[@Javatechie]

Yes we can

[@satishkumar1799]

How can we avoid breaking singleton in case of multiple jvms... May be load balancing case...

[@Javatechie]

Singleton can't be safe in multiple JVM . Singleton : one instance per JVM

[@satishkumar1799]

@@Javatechie Thanks for ur response... can u plzz upload end to end spring rest service based app which maintenance user session using basic authentication..

[@Javatechie]

@@satishkumar1799 yeah sure will upload

[@satishkumar1799]

@@Javatechie Thank You!

[@anirudhjadhav9663]

But bro! If you create an object by using the reflection first and second the getInstance then you will end with two instances.

[@Javatechie]

That's the reason constructor level itself I added null check

[@anirudhjadhav9663]

@@Javatechie Can you try this code:- LazySingleton reflectionInstance = null; Class clazz = Class.forName("LazySingleton "); Constructor s3Constructor = clazz.getDeclaredConstructor(); s3Constructor.setAccessible(true); reflectionInstance = s3Constructor.newInstance(); System.out.println("Reflection hashcode :- " + reflectionInstance .hashCode()); LazySingleton instance1 = LazySingleton.getInstance(); System.out.println("Instance hashcode :- " + instance1.hashCode());

[@sumansatpathy2862]

@@anirudhjadhav9663 Just saw your comments & I had also same doubt. Tried to solve. Could you please check this below sol if that works. Please let me know if you find any catch here. private static boolean isCallFromMyGetInstance = false; private static MySingletonClass obj; private MySingletonClass(){ if(obj!=null || isCallFromMyGetInstance==false) { throw new IllegalStateException("Object can't be created using reflection for this class"); } } public static MySingletonClass getInstance() { if(obj==null) { synchronized (MySingletonClass.class) { if(obj==null) isCallFromMyGetInstance=true; obj=new MySingletonClass(); } } return obj; }

[@AmritAgarwal07]

1 more way is interfaces and enum also singletons[i].reference = new Singleton();

[@saurabhpatil2156]

I can still break your singleton code by executing reflection first and calling getInstance() later. I will have 2 objects of your class