Yes, you can declare an abstract method protected. If you do so you can access it from the classes in the same package or from its subclasses. (Any you must to override an abstract method from the subclass and invoke it.)
Can abstract classes have private variables?
Abstract classes can have private methods. Interfaces can’t. Abstract classes can have instance variables (these are inherited by child classes).
Can abstract classes define variables?
Unlike concrete classes, they merely specify an interface to an object, not an object itself. All you can do with an abstract type is to declare a variable to be of that type. Such a variable can point to any actual object which is a subtype of that abstract class.
Should class variables be private or protected?
It should be private if you want it private, and protected if you want it protected. It depends on their use case but you want them to permissions to be as slim as possible. If you want the variable to be accessible by the instance class protected is the way to go.
Can we use protected variable in another class?
Protected Access Modifier – Protected
Variables, methods, and constructors, which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members’ class. The protected access modifier cannot be applied to class and interfaces.
Can we initialize variable in abstract class?
Constructors:
b. Since an abstract class can have instance variables. Therefore, we can define constructors within the abstract class to initialize instance variables.
Can an abstract class have a constructor?
Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses.
Can abstract classes have static variables?
1) Yes. An abstract class can have a static variable.
Can a abstract class have attributes?
An abstract class can contain attribute or variables, abstract method, and normal method or anyone of them. But the subclass of the abstract class can only implement the abstract method of the abstract class.
Why are encapsulation variables private?
By making the variable a private data member, you can more easily ensure that the value is never negative. On the other hand, if the variable is public, another class could change it to a negative value which can cause other parts of the code to crash.
What are protected variables?
Protected variables are those data members of a class that can be accessed within the class and the classes derived from that class. In Python, there is no existence of “Public” instance variables. However, we use underscore ‘_’ symbol to determine the access control of a data member in a class.
Can protected variables be inherited in Java?
The protected access modifier is accessible within the package. However, it can also accessible outside the package but through inheritance only.
Can private variables be inherited in Java?
Private Members in a Superclass
A subclass does not inherit the private members of its parent class. However, if the superclass has public or protected methods for accessing its private fields, these can also be used by the subclass.
Can abstract class extend another class?
A concrete class is a conventional term used to distinguish a class from an abstract class. And an abstract class cannot be instantiated, only extended. An abstract class can extend another abstract class. And any concrete subclasses must ensure that all abstract methods are implemented.
Can we declare abstract class as final?
Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods.
Can abstract class have getters and setters?
You can do everything in an abstract class that you can do in a normal class except creating a new object only by using a constructor. This means that you can simply copy and paste the getters and setters from your subclass into your parent class.
Can we create object of abstract class?
We cannot create objects of an abstract class. To implement features of an abstract class, we inherit subclasses from it and create objects of the subclass. A subclass must override all abstract methods of an abstract class.
Can we declare interface as final?
interface method can not be final . cannot be declared final.
Can we override 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. The calling of method depends upon the type of object that calls the static method.
Can a abstract class implement an interface?
Java Abstract class can implement interfaces without even providing the implementation of interface methods. Java Abstract class is used to provide common method implementation to all the subclasses or to provide default implementation. We can run abstract class in java like any other class if it has main() method.
Can abstract class have access modifiers in Java?
Abstract Access Modifier is a modifier applicable only for classes and methods but not for variables.
Java.
| Abstract Access Modifier | Public Access Modifier |
|---|---|
| This modifier is more restricted than the public access modifier. | This modifier is less restricted than the abstract access modifier. |
What is Polymorphism in Java?
In Java, polymorphism refers to the ability of a class to provide different implementations of a method, depending on the type of object that is passed to the method. To put it simply, polymorphism in Java allows us to perform the same action in many different ways.
What is the difference between encapsulation and data hiding?
While data hiding focuses on restricting data use in a program to assure data security, data encapsulation focuses on wrapping (or encapsulating) the complex data to present a simpler view to the user. In data hiding, the data has to be defined as private only. In data encapsulation, the data can be public or private.
What is the difference between abstraction and encapsulation?
Abstraction is the method of hiding the unwanted information. Whereas encapsulation is a method to hide the data in a single entity or unit along with a method to protect information from outside. We can implement abstraction using abstract class and interfaces.
Why do we use polymorphism in Java?
Polymorphism is considered one of the important features of Object-Oriented Programming. Polymorphism allows us to perform a single action in different ways. In other words, polymorphism allows you to define one interface and have multiple implementations.
What does a protected variable mean Java?
In Java, protected means that the member can be accessed by any class in the same package and by subclasses even if they are in another packages. Note A protected variable is not visible outside the package. for example B extends A and A has a protected int x; it can be use within the class B.
What is difference between private and protected in Java?
The private modifier specifies that the member can only be accessed in its own class. The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.
What does super () __ Init__ do?
When you initialize a child class in Python, you can call the super(). __init__() method. This initializes the parent class object into the child class. In addition to this, you can add child-specific information to the child object as well.
Can object access protected members?
Protected members in a class are similar to private members as they cannot be accessed from outside the class. But they can be accessed by derived classes or child classes while private members cannot.
Can protected members be inherited?
The protected members are inherited by the child classes and can access them as its own members. But we can’t access these members using the reference of the parent class. We can access protected members only by using child class reference.
Can interface be protected in Java?
In general, the protected members can be accessed in the same class or, the class inheriting it. But, we do not inherit an interface we will implement it. Therefore, the members of an interface cannot be protected.
Are static members inherited to subclasses?
In essence, static members are not inherited, they are just class-level (i.e. universal) methods that are accessible from anywhere.
Is constructor inherited?
Constructors are not inherited. The superclass constructor can be called from the first line of a subclass constructor by using the keyword super and passing appropriate parameters to set the private instance variables of the superclass.
Can abstract class have main () function defined inside it?
Can abstract class have main() function defined inside it? Explanation: This is a property of abstract class. It can define main() function inside it. There is no restriction on its definition and implementation.
Can we extend 2 abstract classes in Java?
You can’t extend two or more classes at one time. Multiple inheritance is not allowed in java.
Can abstract class have private constructor?
Answer: Yes. Constructors in Java can be private. All classes including abstract classes can have private constructors. Using private constructors we can prevent the class from being instantiated or we can limit the number of objects of that class.
Can a constructor be declared static?
No, we cannot define a static constructor in Java, If we are trying to define a constructor with the static keyword a compile-time error will occur. In general, static means class level. A constructor will be used to assign initial values for the instance variables.
Can abstract class have static methods?
Yes, of course you can define the static method in abstract class. you can call that static method by using abstract class,or by using child class who extends the abstract class. Also you can able to call static method through child class instance/object.
Why abstract class has a constructor?
The main purpose of the constructor is to initialize the newly created object. In abstract class, we have an instance variable, abstract methods, and non-abstract methods. We need to initialize the non-abstract methods and instance variables, therefore abstract classes have a constructor.
What happens when we extend abstract class?
Extending an abstract class
Once you extend an abstract class in Java you need to override all the abstractmethods in it or, declare it abstract.
How many abstract methods can an abstract class have?
To create an abstract class, just use the abstract keyword before the class keyword, in the class declaration. You can observe that except abstract methods the Employee class is same as normal class in Java. The class is now abstract, but it still has three fields, seven methods, and one constructor.
How many instances can be created for an abstract class?
0 instances can be created for an abstract class.
The answer to the question of how many instances of an abstract class can be created is zero. That is, we cannot create an instance of an abstract class as it does not have any complete implementation. An abstract class acts like a template or an empty structure.
Can we create instance of interface?
No, you cannot instantiate an interface. Generally, it contains abstract methods (except default and static methods introduced in Java8), which are incomplete. Still if you try to instantiate an interface, a compile time error will be generated saying “MyInterface is abstract; cannot be instantiated”.
Is abstract class always public?
abstract methods have the same visibility rules as normal methods, except that they cannot be private .
Can we declare abstract class as 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.
Can we override interface?
No. Interface methods can be implemented. To overload/override a method, that method must be defined first.
Can we declare a class with static modifier?
The static modifier can be used to declare static classes. In classes, interfaces, and structs, you may add the static modifier to fields, methods, properties, operators, events, and constructors. The static modifier can’t be used with indexers or finalizers.
Can we overload the main () method?
Yes, we can overload the main method in Java, but When we execute the class JVM starts execution with public static void main(String[] args) method.
Can abstract class have attributes?
An abstract class can contain attribute or variables, abstract method, and normal method or anyone of them. But the subclass of the abstract class can only implement the abstract method of the abstract class.
Can an abstract class implement an interface?
This is a class that usually contains at least one abstract method which can’t be instantiated and It is also possible for the class to have no methods at all. The instance of an abstract class can’t be created. Now as all methods in an interface are abstract methods therefore we can implement it using Abstract Class.