Why is java date mutable

Any instance of the class ArrayList is mutable. It's basically a wrapper over a dynamically-sized array. Its elements can be modified. Carrol Raj Pundit. What is singleton class in Java?

Singleton Class in Java. In object-oriented programming, a singleton class is a class that can have only one object an instance of the class at a time. To design a singleton class : Make constructor as private. Write a static method that has return type object of this singleton class. Are tuples mutable? The tuple itself isn't mutable i. Likewise, the string is immutable because strings don't have any mutating methods.

The list object does have mutating methods, so it can be changed. Zacarias Aldermann Pundit. What is mutable vs immutable? What are mutable and immutable data structures? A mutable object is an object whose state can be modified after it is created. An immutable object is an object whose state cannot be modified after it is created. Examples of native JavaScript values that are immutable are numbers and strings.

Yangyang Bloink Pundit. Which is better StringBuffer or StringBuilder? String is immutable whereas StringBuffer and StringBuider are mutable classes. Olida Rigueira Teacher. What is immutable string? String is immutable means that you cannot change the object itself, but you can change the reference to the object. Tran Huesmann Supporter. Why do we need immutable objects in Java?

Actually Shruti want to say that if a Class contain a List. Then how you make it immutable? So in this case, you must return the list instance wrapped in Collections. Hi Lokesh, How we will handle the situation when class is have a instance type of it own type. In TestMain. Hi Ravi, Could you please try some modifications and share with all of us your findings?? Let me know if something interesting you find.

What is the specific need of it? Absolutely no need. As far as you are able to create a fully initialized instance of class, and does not let modify users to change it after, you are free to make it public as well. Nope String is itself immutable so changing string1 and string2 would not change the values in the Immutable class Instance variable say immutableString1 and immutableString2.

Even more to say it would be pointing to a different location in the String pool. That is why cloning was not necessary for Immutable instance variable but if you try the same with date without cloning you would run into problems. Can you please explain about following scenario:. Also, static variables can be accesses only inside static blocks. The simplest way to do this is to declare the class as final.

Final classes in java can not be overridden. But how it make a class immutable? I can still change the state of class by changing the values of fields it contain. When you change the values of the fields the state does not change but, the new object of that class will be created and its reference points to the new object while old object is still in memory. I am not sure if I get your question. But instance variable define the state of the object.

So when somebody says a class is immutable it means once defined nobody can change its state which means that nobody can change its instance variables. So If an Raveesh object of class Employee is created then its instance variable name cannot be changed to Vinay.

Unless a new object with Vinay is created. So if multiple threads are accessing Raveesh object, no one can come in and suddenly change its state to Vinay shocking all the other threads.

Hope it is clear now. Hi, in below code if i have variables and getter and setter for this am i supposed to add them manually in getT method is there any shortcut. You can use BeanUtils. Hi Lokesh, Could you please explain me in brief? To understand this, you must know the concept that Java is pass by value [please read this post]. When you pass reference of t to method tryModification , then there are two reference variables in program referring to same instance of Test.

You can say e. If you change anything in instance of Test by using reference of t1, then t2 will also be able to see it. Both referring to same instance, remember. Will t1 impact?? Assigning null or another instance make t2 to point somewhere else; but t1 is still pointing to original instance.

You see why name value got changed, because reference of Test got skipped outside ImmutableClass. Mutability of Test class, make ImmutableClass mutable as well. To prevent this, you need to return a new instance of Test from getT. This will ensure that original reference of Test does not skip outside the ImmutableClass, so that nobody can change it. Sir, I am a bit confused and would like to ask that whatever we are changing in the tryModification method, we are changing it locally to this method..

Following is your code with little modification package com. Hi Rahul, Thanks for asking this question. Asking a question to clear doubt is always better, then remaining in doubt. When you talk about immutability, always seperate fields in class into two sections: i. All primitives e. Integer, Double and String class are implicitly immutable in java so you do not need to much worry about it. Date class is mutable field so you need to safeguard it with some extra code e.

What we are actually returning a new copy of Date object, so is somebody manipulate it then original copy is unchanged. You are tight that methods receive a local copy to work on, but that copy is actually a copy of reference pointing to original object.

You can not change the reference, but once you have the reference, you can always change the content inside object that reference is pointing to. Thanks for a quick response sir…. And thats what my point is if we get the reference then we can change the content but see the following code…. And one more thing Sir, java supports call by value and not call by reference.. Please clarify my doubts. Sir, I misunderstood one of your point, so am clarify with what you were telling as int is just a primitive data type, its neither mutable or immutable rather it depends upon our implementation… Thanks for your patience and I personally like your blog as it clarifies many things..

Thanks Once again!!! Your welcome. Hello Lokesh, This explanation is somewhat full of confusion. In the Class you have used 3 variables, out of them two are String and Integer which you are trying to modify to show that these cannot be changed as the class is immutable.

But these two variables are itself immutable so these cannot be changed whether the class is mutable or immutable. What is exactly the need of having a static method with the name createNewInstance? We can directly call the constructor when we create a object with new operator.

To be more precise what will be the difference between creating an object directly calling the constructor making it public and having a method to create an instance of the immutable class?

For eg String class has no method which returns void and changes the String. All functions of String class will always return a new String. Similar to that , I suppose having an instance creation method is not needed for making a class Immutable.

Yes, you are right. This method has absolutely nothing to do with immutability of class. The only safe way to do it is to construct a new one every time. The new API in Java 8 has thread-safe formatters and parsers. Like Liked by 1 person.

Go carefully…. The main safe approach to do it is to develop another one without fail. The new API in Java 8 has string safe formatters and parsers. If so, I agree completely. From the JavaDoc, notice the 2nd line in particular.

The factory will alter the values of the second and nanosecond in order to ensure that the stored nanosecond is in the range 0 to ,, Thanks for the details explanation! I have a Date object whose value is coming from the client. Could you pls provide me with some pointers on how could this be achieved? Please ask a new question on Stack Overflow. However, for me personally I understood very early on in my Java career that Date is merely a wrapper around a long ms since epoch and you should think of it as such.

I have used it in the places where I needed an Object rather than a primitive, however often forced to by some library. Those are the people who ask such questions on SO, in my experience. Yes, it is misnamed but then again many things are and the Javadoc opens by saying clearly what Date is , it is mutable but sometimes that is handy if you really need an object and you believe the tales that there is still to this day a cost involved with object creation — albeit negligible — except if you are into low latency, no jitter type of stuff , it can return 61 from the getSeconds method but that method has been in-your-face deprecated since the yearly days of Java, never seen the method used and the toString method does some weird woodo but I never seen anyone use it, except for debug output..

Date for java. Instant in existing code. In fact, unless you need the extra precision that Instant will give you Instant will take up considerable more memory. The real choice in the past has been if you should use a long primitive , a Long or a Date in your code. Depending on the use-case each had its purpose and benefits. To be honest, the problem has never been really been Date, but the lack of all the true date and time classes that java.

Those are great. Calendar has been a greater screw-up than Date in my book. Also SimpleDateFormat has thrown not just newbies but seasoned Java developers off, so that one was is! The name of the identifier tells me that the developer intended it as an instant in time. So now we have java. But in fact — to some degree — I think Date has bigger competitors in long or Long than it does in java. All this being said it may be I have just forgotten the early days of learning and blissfully trying to forget all the misunderstanding I did at the time.

That is, how many days are there for this month. LocalTime: The LocalTime provides only time with out date information. LocalTime; import java. LocalDateTime; import java. Year: The Year provides year information. Year; import java. Duration: The Duration provides quantity or amount of time in terms of seconds and nanoseconds.

Duration; import java. DAYS ; System. Period: The Duration provides a quantity or amount of time in terms of years, months and days. Period; import java.