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Can interface methods have return type?
3 Answers. If the return type must be the type of the class that implements the interface, then what you want is called an F-bounded type: This is typically used to declare things like clone() or copy() methods that are well-typed. As another example, it’s used by java.
CAN interfaces contain concrete methods?
Interfaces cannot have any concrete methods. If you need the ability to have abstract method definitions and concrete methods then you should use an abstract class. Java 8 has default methods, which is basically what you’re asking about.
What type of methods does an interface contain?
The interface body can contain abstract methods, default methods, and static methods. An abstract method within an interface is followed by a semicolon, but no braces (an abstract method does not contain an implementation).
What will happen if we define a concrete method in an interface?
It’s a feature that allows developers to add new methods to an interface without breaking the existing implementations of these. It provides flexibility to allow interface define implementation which will use as default in the situation where a concrete class fails to provide an implementation for that method.
Can an interface have fields?
An interface can’t contain instance fields, instance constructors, or finalizers. Interface members are public by default, and you can explicitly specify accessibility modifiers, such as public , protected , internal , private , protected internal , or private protected .
What happens if we define concrete method inside interface?
Q) What happens, if we define concrete method inside Interface ? Concrete method (method with body) are allowed with default or static keyword prefixed, as shown below Q) Can a method inside an interface be declared as final ?
Can you create an object for an interface?
Since, interface doesn’t have constructor and contains only abstract methods and constants therefore we don’t need to instantiate Instead implementing classes provide concrete implementation for these abstract methods and constants can be accessed using . Q) Can we create an object for an interface ?
Can a method inside an interface be declared as final?
Concrete method (method with body) are allowed with default or static keyword prefixed, as shown below Q) Can a method inside an interface be declared as final ? By default, methods declared inside interface are public & abstract even if we don’t declare it explicitly compiler adds these modifier during compilation time
Can a final modifier be used in an interface?
Still, final modifier is not allowed in any of the methods in interface i.e.; abstract, default & static methods Q) What happens, if we don’t initialize variables inside Interface ? As variables defined inside interface are by default public, static & final.