What is the concept of Immutability for strings in Java? Why are strings immutable? Non-static variable cannot be referenced from a static context. What is blank final variable? How to execute a python file with few arguments in java? Why are you not able to declare a class as static in Java? Why it is not possible to define a static method in a Java interface? Welcome back to the World's most active Tech Community!
Password must have. Please enter a valid emailid. You may like. Interview Questions. Programming Questions. Can I define an array of size 0? Can I define an array with negative size? Since java does not support multiple inheritance in case of class, but by using interface it can achieve multiple inheritance. It is also used to achieve loose coupling.
A Java class can only extend one parent class. Interfaces are not classes, however, and an interface can extend more than one parent interface. The extends keyword is used once, and the parent interfaces are declared in a comma-separated list. 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. A class that implements an interface needs to implement them all as instance methods. You can only have one direct abstract superclass. Therefore, interfaces are useful if you need to expose two or more interfaces. Interface is basically a reference to combine two corelated but different entity. Think of a web application where you have interface defined and other classes implement it.
As you cannot create an instance of interface to access the variables you need to have a static keyword. Since its static any change in the value will reflect to other instances which has implemented it. So in order to prevent it we define them as final. Just tried in Eclipse, the variable in interface is default to be final, so you can't change it. Compared with parent class, the variables are definitely changeable. From my point, variable in class is an attribute which will be inherited by children, and children can change it according to their actual need.
On the contrary, interface only define behavior, not attribute. The only reason to put in variables in interface is to use them as consts which related to that interface.
Though, this is not a good practice according to following excerpt:. As well, the constants used by a class are typically an implementation detail, but placing them in an interface promotes them to the public API of the class.
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Ask Question. Asked 11 years, 8 months ago. Active 1 year, 9 months ago. Viewed k times. Why are interface variables static and final by default in Java? Improve this question. Jothi Jothi You shouldn't put any variables inside Interfaces. Because interfaces define contracts which can be implemented in various ways. The value of a variable is implementation. We certainly can when we know all the classes implementing the interface have some constant variables Field names for instance.
Is it a good idea to make a variable in a class an instance of the interface that the class implements? I have heard this before. Answer by Arun Raaj answered Apr 24 '18 at and comment by denis Aug 17 '17 at correctly identify Multiple Inheritance as the main issue Show 2 more comments. Active Oldest Votes.
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