Can abstract class be instantiated?

Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract .

Why abstract classes Cannot be instantiated?

We cannot instantiate an abstract class in Java because it is abstract, it is not complete, hence it cannot be used.

When can an abstract class be instantiated?

An abstract class cannot be instantiated. Instead it defines (and, optionally, partially implements) the interface for any class that might extend it.

Is abstract class must be instantiated?

An abstract class cannot be instantiated directly, i.e. the object of such class cannot be created directly using the new keyword. An abstract class can be instantiated either by a concrete subclass or by defining all the abstract method along with the new statement.

Can abstract class be instantiated using new operator?

An abstract class cannot be instantiated using the new operator, but you can still define its constructors, which are invoked in the constructors of its subclasses. For instance, the constructors of GeometricObject are invoked in the Circle class and the Rectangle class.

Can we instantiate abstract class

Can we call constructor of abstract class?

The constructor inside the abstract class can only be called during constructor chaining i.e. when we create an instance of sub-classes. This is also one of the reasons abstract class can have a constructor.

Can we inherit abstract class?

An abstract class cannot be inherited by structures. It can contains constructors or destructors. It can implement functions with non-Abstract methods.

Can we declare a class as static?

So, Yes, you can declare a class static in Java, provided the class is inside a top-level class. Such clauses are also known as nested classes and they can be declared static, but if you are thinking to make a top-level class static in Java, then it's not allowed.

Can an interface be instantiated?

An interface can't be instantiated directly. Its members are implemented by any class or struct that implements the interface. A class or struct can implement multiple interfaces.

Is abstract and Cannot be instantiated?

Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract .

Can constructor be inherited?

Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass.

Can we create static method in interface?

Static methods in an interface since java8

Since Java8 you can have static methods in an interface (with body). You need to call them using the name of the interface, just like static methods of a class.

Can an abstract class be extended?

An abstract class can extend another abstract class. And any concrete subclasses must ensure that all abstract methods are implemented. Abstract classes can themselves have concrete implementations of methods. These methods are inherited just like a method in a non-abstract class.

Can abstract class be public?

Abstract classes shouldn't have public constructors because they don't make sense. Abstract classes are incomplete, so allowing a public constructor (which anyone could call) wouldn't work as you can't instantiate an instance anyway.

Why can't we instantiate an interface?

You can't instantiate an interface or an abstract class because it would defy the object oriented model. Interfaces represent contracts - the promise that the implementer of an interface will be able to do all these things, fulfill the contract.

Can abstract class have static methods in Java?

If you declare a method in a class abstract to use it, you must override this method in the subclass. But, overriding is not possible with static methods. Therefore, an abstract method cannot be static.

Can an interface have a constructor?

No, you cannot have a constructor within an interface in Java. You can have only public, static, final variables and, public, abstract, methods as of Java7. From Java8 onwards interfaces allow default methods and static methods. From Java9 onwards interfaces allow private and private static methods.

Can we declare interface as 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 we instantiate runnable interface?

You cannot instantiate an interface. Nor an abstract class.

Can constructor be static?

A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed only once. It is called automatically before the first instance is created or any static members are referenced.

Can a class be private?

Yes, we can declare a class as private but these classes can be only inner or nested classes. We can't a top-level class as private because it would be completely useless as nothing would have access to it.

Can we create immutable class in Java?

Immutable class in java means that once an object is created, we cannot change its content. In Java, all the wrapper classes (like Integer, Boolean, Byte, Short) and String class is immutable. We can create our own immutable class as well.

Can we create object for interface?

No, you cannot instantiate an interface. Generally, it contains abstract methods (except default and static methods introduced in Java8), which are incomplete.

Can a final class be inherited?

If a class is marked as final then no class can inherit any feature from the final class. You cannot extend a final class.

Can we inherit static class in Java?

Static methods do not use any instance variables of any object of the class they are defined in. Static methods take all the data from parameters and compute something from those parameters, with no reference to variables. We can inherit static methods in Java.