Quick Answer: How Many Methods Can An Interface Have?

Can an interface have methods?

Like a class, an interface can have methods and variables, but the methods declared in an interface are by default abstract (only method signature, no body).

Interfaces specify what a class must do and not how.

It is the blueprint of the class..

Can an interface be final?

If you make an interface final, you cannot implement its methods which defies the very purpose of the interfaces. Therefore, you cannot make an interface final in Java. Still if you try to do so, a compile time exception is generated saying “illegal combination of modifiers − interface and final”.

CAN interface have private methods?

As of Java 9, methods in an interface can be private. A private method can be static or an instance method, but it cannot be a default method since that can be overridden.

What happens if you give method body in interface?

It is a compile-time error if a method declared in an interface is declared static, because static methods cannot be abstract. … A static method also has a block body, which provides the implementation of the method. So it explicitly states that in Java 8, they can exist.

How many abstract methods can an interface have?

Type of methods: Interface can have only abstract methods. Abstract class can have abstract and non-abstract methods. From Java 8, it can have default and static methods also.

What is a interface?

In general, an interface is a device or a system that unrelated entities use to interact. … Unlike a class, an interface never implements methods; instead, classes that implement the interface implement the methods defined by the interface. A class can implement multiple interfaces.

How many default methods can an interface have?

With default functions in interfaces, there is a possibility that a class is implementing two interfaces with same default methods. The following code explains how this ambiguity can be resolved.

Which method Cannot be overridden?

A method declared final cannot be overridden. A method declared static cannot be overridden but can be re-declared. If a method cannot be inherited, then it cannot be overridden. A subclass within the same package as the instance’s superclass can override any superclass method that is not declared private or final.

Can we define variables in interface?

In Java , interface doesn’t allow you to declare any instance variables. Using a variable declared in an interface as an instance variable will return a compile time error. You can declare a constant variable, using static final which is different from an instance variable.

When would you use an interface?

You should use an interface if you want a contract on some behavior or functionality. You should not use an interface if you need to write the same code for the interface methods. In this case, you should use an abstract class, define the method once, and reuse it as needed.

What is the purpose of interface?

An interface is a programming structure/syntax that allows the computer to enforce certain properties on an object (class). For example, say we have a car class and a scooter class and a truck class.

How many interfaces can a class have?

To declare a class that implements an interface, you include an implements clause in the class declaration. Your class can implement more than one interface, so the implements keyword is followed by a comma-separated list of the interfaces implemented by the class.

Can an interface contain constants?

Java programmers commonly define constants inside their interfaces, if it makes design sense. You can do so using variables in an interface because the values will be present instantly at runtime and their values shared among all classes implementing your interface, because they are static and final.

Can we write method body in interface?

All methods of an Interface do not contain implementation (method bodies) as of all versions below Java 8. … Interfaces cannot be instantiated, but rather are implemented. A class that implements an interface must implement all of the non-default methods described in the interface, or be an abstract class.

Can interface contain static methods?

An interface in Java is similar to class but, it contains only abstract methods and fields which are final and static. … You can access static methods using class name without instantiation.