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Why an interface can not have anything but constants and abstract methods?
Wiki User
∙ 11y ago
The idea is that an interface is not a class, it is just a specification of what classes that implement it must contain.
Wiki User
∙ 11y ago
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What kind of constructs can be declared in a Java interface?
Constants and abstract methods. That's it.
What is the major difference between an Interface and a Class?
An interface can only have abstract methods or constants in it. A class can have both that and everything else in Java.
Abstract class vs interface?
Comparison between an Abstract Class and an Interface:While an abstract class can define both abstract and non-abstract methods, an interface can have only abstract methods. Another way interfaces differ from abstract classes is that interfaces have very little flexibility in how the methods and variables defined in the interface are declared. These rules are strict:
What do mean by interface in java?
An interface in Java is like an abstract class, but there are no method bodies allowed in it and it has to be declared with the interface keyword. It is Java's way of getting around the Deadly Diamond of Death. Only abstract methods and constants are allowed in it.
What is difference between interface and abstract in java?
While an abstract class can define both abstract and non-abstract methods, an interface can have only abstract methods. Another way interfaces differ from abstract classes is that interfaces have very little flexibility in how the methods and variables defined in the interface are declared. These rules are strict: • All interface methods are implicitly public and abstract. In other words, you do not need to actually type the public or abstract modifiers in the method declaration, but the method is still always public and abstract. (You can use any kind of modifiers in the Abstract class) • All variables defined in an interface must be public, static, and final-in other words, interfaces can declare only constants, not instance variables. • Interface methods must not be static. • Because interface methods are abstract, they cannot be marked final, strictfp, or native. (More on these modifiers later.) • An interface can extend one or more other interfaces. • An interface cannot extend anything but another interface. • An interface cannot implement another interface or class. • An interface must be declared with the keyword interface. You must remember that all interface methods are public and abstract regardless of what you see in the interface definition.
What are the differences between an abstract class and an interface in java?
They are very different. An abstract class is a class that represents an abstract concept (google define "abstract" if you're unsure) such as 'Thoughts' or 'BankAccount'. When a class is defined as abstract it cannot be used (directly) to create an object. Abstract classes are used as super-classes so that all of their subclasses inherit all methods. Interfaces can be thought of as contracts with all of their implementing classes. They simply require all implementing classes to have methods with the same signature as that defined in the interface, but such methods can behave as appropriate. Hope that helps :)
What is interface in java?
Interface is collection of abstract methods which has only declaration and no implementation
What is an interface class and what is an abstract class?
The term interface class does not exist in C#. If this is a term describing a class being an interface to other component (human, subsystems, etc), it is very application specific. The designer of that application should know the abstraction.However, C# does have another type called interface. An interface is NOT a class. An interface defines the intention of some behaviors that classes may be extended it and provides the implementation. The intention, is nothing but method signatures, which defines the return data type, the method name, and any method arguments and associated data type. The implementation is the code of the method. Interface is used for separating the concern of design and implementation.Abstract class is a class with abstract keyword. It can be just like a class without that keyword (then, why it is an abstract class?). But it may have some methods or properties defined as abstract. These abstract methods, like the method signatures of an interface, defines the intention.The subclasses of such an abstract class would need to implement those abstract methods (providing the code).There are more common, differences between interfaces and abstract classes, please see answer(s) of those related questions in C# category.
What is the difference between an interface and an abstract class?
We can't instantiate both interfaces and abstract classes.The only one difference between them is that an interface can't contain concrete(fully defined) methods where as an abstract class may contain them.An abstract class not necessarily contain abstract methods. we can make a class as abstract class even it does not has any abstract methods.When there is a need to write both abstract and concrete methods in a single unit we have to use an abstract class instead of an interface since an interface cant contain concrete methods.All the fields(or properties) of an interface are by default 'static final' even when you don't mention explicitly. And all methods are 'public abstract'.But in an abstract class we can have any type of fields and methods.
Can you have an interface without any abstract method?
My answer to "Can an interface without any abstract method?" is YES.If abstract methods do not include the properties, then this interface should have at least 1 property (get or set) defined. It makes sense to have at least one of the abstract method or property/mutator/getter-setter.If the interface contains no properties, no methods, I cannot think of a reason to create such an interface, meaning - it is useless.
What do you mean when you say that Java has two concepts?
You are talking about the implementation point view of Abstract class and the interface. Let's go. 1. Interface helps Multiple inheritance:- In java you can't have a class inherited from more than one class, i.e. the multiple inheritance. Interface helps us in implementing the multiple inheritance(virtually), because their is no such restriction in implementing more than one interface. But the Abstract class can't help you doing so. 2. Interface helps global declaration:- In C/C++, a header file holds the declaration of the functions and the symbolic constants. Similarly we can have a interface which is having only the symbolic constants which is same for all classes which implements it. And also the method have only the signature and the class which implements it is free to write the body at his own wish. Abstract class can't help in doing this. 3. Abstract class is more secure:- Because in Interface we have all the things public. But in Abstract class we can have private and also friendly members. 4. Interface is overhead:- Because in Interface we are bound to implement all the methods though some of them we actually need. But in case of the Abstract class we can override the methods which we want.
What is difference between interface and abstract class?
All the methods declared inside an Interface are abstract. Where as abstract class must have at least one abstract method and others may be concrete or abstract. In Interface we need not use the keyword abstract for the methods.
