Quick Answer: Can We Write Main Method In Interface?

How do you write default method in interface?

Default methods can be provided to an interface without affecting implementing classes as it includes an implementation.

If each added method in an interface is defined with implementation, then no implementing class is affected.

An implementing class can override the default implementation provided by the interface..

Why static methods are not allowed in interface?

Any method you write in an interface can’t rely on any implementation details. As an example in favor of static methods in interfaces, consider utility classes like Collections in the Java API. That class only exists because those static methods can’t be declared in their respective interfaces.

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.

Can we declare static method inside interface?

You can’t define static methods in an interface because static methods belongs to a class not to an instance of class, and interfaces are not Classes. Read more here. In this case what you have is two classes with 2 distinct static methods called methodX().

Can an interface have main () method?

Answer : Yes, we can provide different implementation of main() declared in an interface and classes implementing that interface by overriding method and can overload static main method if defined in an interface. Some more information regarding interface changes in Java 8.

What is default method?

Default methods enable you to add new functionality to existing interfaces and ensure binary compatibility with code written for older versions of those interfaces. In particular, default methods enable you to add methods that accept lambda expressions as parameters to existing interfaces.

Is it compulsory to implement all methods of interface?

Yes, it is mandatory to implement all the methods in a class that implements an interface until and unless that class is declared as an abstract class. … Declare the class as an abstract class, as a result, forces you to subclass the class (and implement the missing methods) before you can create any objects.

Can we override default method of interface?

If you have default method in an interface, it is not mandatory to override (provide body) it in the classes that are already implementing this interface. In short, you can access the default methods of an interface using the objects of the implementing classes.

Can we write concrete methods in interface?

1. Interface. Interface is a blueprint for your class that can be used to implement a class ( abstract or not); the point is interface cannot have any concrete methods. Concrete methods are those methods which have some code inside them; in one word – implemented.

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 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 have 2 default method in interface?

Multiple Defaults 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. First solution is to create an own method that overrides the default implementation.

What is the use of static method in interface?

Java interface static method helps us in providing security by not allowing implementation classes to override them. We can’t define interface static method for Object class methods, we will get compiler error as “This static method cannot hide the instance method from Object”.

Can abstract class have method body?

A class that is declared using “abstract” keyword is known as abstract class. It can have abstract methods(methods without body) as well as concrete methods (regular methods with body). A normal class(non-abstract class) cannot have abstract methods.

What is difference between abstract class and interface?

Abstract class can inherit another class using extends keyword and implement an interface. Interface can inherit only an inteface. Abstract class can be inherited using extends keyword. Interface can only be implemented using implements keyword.

Can we write method definition in interface?

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). … If a class implements an interface and does not provide method bodies for all functions specified in the interface, then the class must be declared abstract.

Can we override static method?

Can we override a static method? No, we cannot override static methods because method overriding is based on dynamic binding at runtime and the static methods are bonded using static binding at compile time. So, we cannot override static methods.

Can abstract class have private method?

Abstract methods in an abstract class cannot be private but can be of specifiers public, protected or default. Similarly, any class cannot be protected or private (can be only public or default). … Abstract method or concrete method in abstract class can be protected (a program is available at the end).

Can we make static method in interface?

Similar to Default Method in Interface, the static method in an interface can be defined in the interface, but cannot be overridden in Implementation Classes. To use a static method, Interface name should be instantiated with it, as it is a part of the Interface only.