By the way, this example doesn't show, whether you can overload static method or not, but you can. See this tutorial, for an example of an overloading static method in Java. That's all on this Java interview question guys. Remember, Static methods can not be overridden in Java , but they can be overloaded and hidden in Java. We have also touched based on What is method hiding in Java, and learned Why Static method can not be overridden in Java , since they are bonded during compile time by using a type of Class, and not at runtime using Objects.
Why wait and notify methods are declared in Object class? Why multiple Inheritance is not supported in Java? Difference between Synchronized and ReentrantLock in Java. Why main method is public, static and void in Java?
Why Character array is preferred over String for storing password in Java. Share to Twitter Share to Facebook. Labels: core java , core java interview question , object oriented programming. March 18, at AM Anonymous said AlienOnEarth, it's not overriding but hiding, static variables are resolved at compile time by using Type of variable, Sine you are accessing them in TestParent class, it's print "test" October 2, at AM Anonymous said January 5, at AM.
Newer Post Older Post Home. Subscribe to: Post Comments Atom. Subscribe for Discounts and Updates Follow. Search This Blog. Interview Questions core java interview question data structure and algorithm 78 Coding Interview Question 75 interview questions 70 design patterns 35 SQL Interview Questions 34 object oriented programming 34 thread interview questions 30 spring interview questions 28 collections interview questions 25 database interview questions 16 servlet interview questions 15 Programming interview question 6 hibernate interview questions 6.
How to design a vending machine in Java? How HashMap works in Java? Why String is Immutable in Java? Translate This Blog. ClassNotFoundException: org. Law of Demeter in Java - Principle of least Knowle When to Make a Method Static in Java? Is it possible to have an abstract method in a fin Top 5 Courses to learn Groovy and Grails in Why Enum Singleton are better in Java?
Difference between repaint and revalidate method i How to Count number of Set bits or 1's of Integer When a class is loaded and initialized in JVM - Ja Is Swing Thread Safe in Java? In reality, Ruby does not have "static" methods as far as I could find - in that case these are methods on the singleton class object. You can then override this singleton with a new class and the methods in the previous class object will call those defined in the new class correct? So if you called a method in the context of the original class it still would only execute the original statics, but calling a method in the derived class, would call methods either from the parent or sub-class.
Interesting and I can see some value in that. It takes a different thought pattern. Since you are working in Java, you will need to adjust to that way of doing things. Why they did this? Well, probably to improve performance at the time based on the technology and understanding that was available. Computer languages are constantly evolving. Go back far enough and there is no such thing as OOP.
In the future, there will be other new ideas. EDIT : One other comment. Java static methods are not the same as Ruby class methods. I can see how this would also be greatly confusing by the fact that Java also uses "class method" as another way to talk about static methods but this same term is used differently by Ruby.
Java does not have Ruby style class methods sorry ; Ruby does not have Java style static methods which are really just old procedural style functions, as found in C. By the way - thanks for the question! I learned something new for me today about class methods Ruby style. But, you don't get any compiler error if you try to override a static method. That means, if you try to override, Java doesn't stop you doing that; but you certainly don't get the same effect as you get for non-static methods.
Overriding in Java simply means that the particular method would be called based on the run time type of the object and not on the compile time type of it which is the case with overriden static methods. Because they are class methods and hence access to them is always resolved during compile time only using the compile time type information. Accessing them using object references is just an extra liberty given by the designers of Java and we should certainly not think of stopping that practice only when they restrict it Example : let's try to see what happens if we try overriding a static method Notice the second line of the output.
Had the staticMethod been overriden this line should have been identical to the third line as we're invoking the 'staticMethod ' on an object of Runtime Type as 'SubClass' and not as 'SuperClass'. This confirms that the static methods are always resolved using their compile time type information only. In general it doesn't make sense to allow 'overriding' of static methods as there would be no good way to determine which one to call at runtime.
Taking the Employee example, if we call RegularEmployee. In the case of Java, one could imagine a language definition where it is possible to 'override' static methods as long as they are called through an object instance. However, all this would do is to re-implement regular class methods, adding redundancy to the language without really adding any benefit. By overriding we can create a polymorphic nature depending on the object type.
Static method has no relation with object. So java can not support static method overriding. I agree that this is the bad design of Java. Many other languages support overriding static methods, as we see in previous comments. I feel Jay has also come to Java from Delphi like me. Delphi Object Pascal was one of the languages implementing OOP before Java and one of the first languages used for commercial application development.
It is obvious that many people had experience with that language since it was in the past the only language to write commercial GUI products. And - yes, we could in Delphi override static methods. Actually, static methods in Delphi are called "class methods", while Delphi had the different concept of "Delphi static methods" which were methods with early binding.
To override methods you had to use late binding, declare "virtual" directive. So it was very convenient and intuitive and I would expect this in Java. By overriding, you achieve dynamic polymorphism.
When you say overriding static methods, the words you are trying to use are contradictory. Static says - compile time, overriding is used for dynamic polymorphism. Both are opposite in nature, and hence can't be used together. Dynamic polymorphic behavior comes when a programmer uses an object and accessing an instance method. JRE will map different instance methods of different classes based on what kind of object you are using.
When you say overriding static methods, static methods we will access by using the class name, which will be linked at compile time, so there is no concept of linking methods at runtime with static methods.
So the term "overriding" static methods itself doesn't make any meaning. Note: even if you access a class method with an object, still java compiler is intelligent enough to find it out, and will do static linking. What good will it do to override static methods. You cannot call static methods through an instance.
EDIT : It appears that through an unfortunate oversight in language design, you can call static methods through an instance. Generally nobody does that. My bad. Overriding in Java simply means that the particular method would be called based on the runtime type of the object and not on the compile-time type of it which is the case with overridden static methods.
As static methods are class methods they are not instance methods so they have nothing to do with the fact which reference is pointing to which Object or instance, because due to the nature of static method it belongs to a specific class. You can redeclare it in the subclass but that subclass won't know anything about the parent class' static methods because, as I said, it is specific to only that class in which it has been declared.
Answer of this question is simple, the method or variable marked as static belongs to the class only, So that static method cannot be inherited in the sub class because they belong to the super class only. In my system, I have SingletonsRegistry class, which returns instance for passed Class.
If instance is not found, it is created. A Static method, variable, block or nested class belongs to the entire class rather than an object.
Here, as the method is static i. High Cohesion - One class should have only one role. For example: A car class should produce only car objects and not bike, trucks, planes etc. But the Car class may have some features behaviour that belongs to itself only. Therefore, while designing the java programming language. The language designers thought to allow developers to keep some behaviours of a class to itself only by making a method static in nature. The below piece code tries to override the static method, but will not encounter any compilation error.
This is because, here we are not overriding a method but we are just re-declaring it. Removing the static keyword from getVehileNumber method of Car class will result into compilation error, Since, we are trying to change the functionality of static method which belongs to Vehicle class only.
Also, If the getVehileNumber is declared as final then the code will not compile, Since the final keyword restricts the programmer from re-declaring the method. Overall, this is upto software designers for where to use the static methods. I personally prefer to use static methods to perform some actions without creating any instance of a class.
Secondly, to hide the behaviour of a class from outside world. Here is a simple explanation. A static method is associated with a class while an instance method is associated with a particular object. Overrides allow calling the different implementation of the overridden methods associated with the particular object.
So it is counter-intuitive to override static method which is not even associated with objects but the class itself in the first place. So static methods cannot be overridden based on what object is calling it, it will always be associated with the class where it was created. Now seeing above answers everyone knows that we can't override static methods, but one should not misunderstood about the concept of accessing static methods from subclass.
We can access static methods of super class with subclass reference if this static method has not been hidden by new static method defined in sub class.
See Java oracle docs and search for What You Can Do in a Subclass for details about hiding of static methods in sub class.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Why doesn't Java allow overriding of static methods? Ask Question. Asked 11 years, 9 months ago. Active 1 year, 4 months ago. Viewed k times.
Why is it not possible to override static methods? If possible, please use an example. Improve this question. Saurabh Gokhale Saurabh Gokhale Most OOP languages don't allow this. Also see stackoverflow. Show 2 more comments. Active Oldest Votes. Improve this answer. Nathan Hughes Nathan Hughes 88k 19 19 gold badges silver badges bronze badges. For instance, Scala's equivalent of "static classes" which are called objects allow overloading of methods.
Objective-C also allows overriding class methods. There is a compile-time type hierarchy and a run-time type hierarchy. It makes perfect sense to ask why a static method call doesn't avail itself of the run-time type hierarchy in those circumstances where there is one. In Java this happens when calling a static method from an object obj. When the static call is in a non-static method of a class, the "current" object could be a derived type of the class -- but static methods defined on the derived types are not considered they are in the run-time type hierarchy.
I should have made it clear: it is not true that the concept is not applicable. This answer, while correct, is more akin to "how it is" rather than how it should be or more accurately how it could be in order to meet the expectations of the OP and, hence here, myself and others. There is no concrete reason to disallow the overriding of static methods other than "that's how it is". I think it's a flaw personally.
Show 10 more comments. But it doesn't work. Find centralized, trusted content and collaborate around the technologies you use most. Connect and share knowledge within a single location that is structured and easy to search. Static methods can not be overridden in the exact sense of the word, but they can hide parent static methods. In practice it means that the compiler will decide which method to execute at the compile time, and not at the runtime, as it does with overridden instance methods.
For a neat example have a look here. And this is java documentation explaining the difference between overriding instance methods and hiding class static methods.
Overriding: Overriding in Java simply means that the particular method would be called based on the run time type of the object and not on the compile time type of it which is the case with overriden static methods.
Hiding: Parent class methods that are static are not part of a child class although they are accessible , so there is no question of overriding it. Even if you add another static method in a subclass, identical to the one in its parent class, this subclass static method is unique and distinct from the static method in its parent class.
Static methods can not be overridden because there is nothing to override, as they would be two different methods. For example. Static methods cannot be overridden because they are not dispatched on the object instance at runtime.
The compiler decides which method gets called. Static methods can be overloaded meaning that you can have the same method name for several methods as long as they have different parameter types. Parent class methods that are static are not part of a child class although they are accessible , so there is no question of overriding it.
Static methods can not be overridden because they are not part of the object's state. Rather, they belongs to the class i.
It is ok to overload static and final methods. If I m calling the method by using SubClass name MysubClass then subclass method display what it means static method can be overridden or not. Static methods is a method whose single copy shared by all the objects of the class.
Static method belongs to the class rather than objects. In case of method overloading , methods should be in the same class to overload. But in case of method overriding , the method in the super class and the method in the sub class act as different method. Overloading is also called static binding, so as soon as the word static is used it means a static method cannot show run-time polymorphism. We cannot override a static method but presence of different implementations of the same static method in a super class and its sub class is valid.
Its just that the derived class will hide the implementations of the base class. For static methods, the method call depends on the type of reference and not which object is being referred, i. Static method belongs only to a class and not its instances , so the method call is decided at the compile time itself. Whereas in case of method overloading static methods can be overloaded iff they have diff number or types of parameters.
If two methods have the same name and the same parameter list then they cannot be defined different only by using the 'static' keyword. No,Static methods can't be overriden as it is part of a class rather than an object. But one can overload static method. Note: if we call a static method with object reference, then reference type class static method will be called, not object class static method. The very purpose of using the static method is to access the method of a class without creating an instance for it.
It will make no sense if we override that method since they will be accessed by classname. No, you cannot override a static method. The static resolves against the class, not the instance. Each class has a static method getCName. When you call on the Class name it behaves as you would expect and each returns the expected value. No surprises in this unit test. But this is not overriding. This declaring something that has a name collision. If we try to reach the static from an instance of the class not a good practice , then it really shows:.
Even though cp is a Child, the static is resolved through the declared type, Parent, instead of the actual type of the object. For non-statics, this is resolved correctly because a non-static method can override a method of its parent.
You can overload a static method but you can't override a static method. Actually you can rewrite a static method in subclasses but this is not called a override because override should be related to polymorphism and dynamic binding.
0コメント