Why does abstract class have constructor?
1) Abstract classes have constructors and those constructors are always invoked when a concrete subclass is instantiated. We know that when we are going to instantiate a class, we always use constructor of that class. Now every constructor invokes the constructor of its super class with an implicit call to super() .
What is the use of abstract constructor?
Abstract constructors will frequently be used to enforce class constraints or invariants such as the minimum fields required to setup the class. NOTE: As there is no default (or no-arg) constructor in the parent abstract class, the constructor used in subclass must explicitly call the parent constructor.
How do you call an abstract constructor?
5 Answers. You can define a constructor in an abstract class, but you can’t construct that object. However, concrete sub-classes can (and must) call one of the constructors defined in the abstract parent class. You can’t call an abstract class constructor with a class instance creation expression, i.e.
What is constructor example?
A constructor in Java is similar to a method that is invoked when an object of the class is created. Here, Test() is a constructor. It has the same name as that of the class and doesn’t have a return type.
Can a constructor be abstract?
You can’t have an abstract constructor, as abstract means you need to provide the implementation for that at some point of time in your subclass. But you cannot override constructor. There will be no point in having an abstract constructor : Since the constructor needs to be of the same name as of class.
Can abstract method have body?
Abstract methods cannot have body. Abstract class can have static fields and static method, like other classes.
Can we declare constructor as abstract?
Yes, an abstract class can have a constructor in Java. You can either explicitly provide a constructor to the abstract class or if you don’t, the compiler will add a default constructor of no argument in the abstract class. This is true for all classes and it also applies to an abstract class.
Why can’t a constructor be final?
i.e. The purpose of making a method final is to prevent modification of a method from outside (child class). In inheritance whenever you extend a class. In other words, constructors cannot be inherited in Java therefore you cannot override constructors. So, writing final before constructors makes no sense.
What happens if an abstract method is not defined?
A method which does not have body is known as abstract method. To use an abstract method, you need to inherit it by extending its class and provide implementation to it. A class which contains 0 or more abstract methods is known as abstract class.
Why does an abstract class need a constructor?
Purpose of constructor is abstract classes may contain fields and sometimes they need to be initialized somehow by using constructor. This chaining of constructors is one of the reasons abstract class can have constructors in Java. Abstract class has fields X and Y.
What is the use of an abstract class constructor?
In general, a class constructor is used to initialize fields. Along the same lines, an abstract class constructor is used to initialize fields of the abstract class.
Can We have constructor in abstract class?
Abstract class can have a constructor though it cannot be instantiated. But the constructor defined in an abstract class can be used for instantiation of concrete class of this abstract class.
Can you create an object of an abstract class?
You cannot create an object of an abstract class type; however, you can use pointers and references to abstract class types. A class that contains at least one pure virtual function is considered an abstract class.