Can abstract classes have constructors in Java?
Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses.
Why do abstract classes have constructors in Java?
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.
How do you call a constructor from an abstract class?
You can’t call an abstract class constructor with a class instance creation expression, i.e. As constructors of abstract classes can only be called within subclass constructors (and by chaining one to another within the same class), I typically make them protected making them public would serve no purpose.
Is it OK to call abstract method from constructor in Java?
It’s a very bad practice to call an abstract method from a constructor. Methods called from constructors should always be private or final, to prevent overriding.
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.
What is the use of constructor in abstract class?
A constructor is used to initialize an object not to build the object. As we all know abstract classes also do have a constructor. So if we do not define any constructor inside the abstract class then JVM (Java Virtual Machine) will give a default constructor to the abstract class.
Should Abstract classes have constructors?
Since an abstract class can have variables of all access modifiers, they have to be initialized to default values, so constructor is necessary. As you instantiate the child class, a constructor of an abstract class is invoked and variables are initialized.
Does abstract class have default constructor?
Can abstract class have final methods?
As a final class cannot be inherited. However, an abstract class can have a final method. This final method is treated like a normal method with a body which cannot be overridden.
Can abstract class contain constructor?
Constructor is always called by its class name in a class itself. A constructor is used to initialize an object not to build the object. As we all know abstract classes also do have a constructor.
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 abstract classes be final?