Can we declare constructor as private?
Yes, we can declare a constructor as private
. If we declare a constructor as private we are not able to create an object of a class. We can use this private constructor in the Singleton Design Pattern.
Can constructor be private or protected?
No, Constructors can be public , private , protected or default
(no access modifier at all). Making something private doesn’t mean nobody can access it. It just means that nobody outside the class can access it. So private constructor is useful too.
Which can be declared as private constructor?
We can declare a constructor private
by using the private access specifier
. Note that if a constructor is declared private, we are not able to create an object of the class. Instead, we can use this private constructor in Singleton Design Pattern.
Can constructor have private?
Yes, a constructor can be private
.
When should a constructor be private?
Private constructors are used
to prevent creating instances of a class when there are no instance fields or methods
, such as the Math class, or when a method is called to obtain an instance of a class. If all the methods in the class are static, consider making the complete class static.
Can we declare constructor as static?
So,
it is illegal to declare a constructor as static
. Thus, it will violate the whole motive of the inheritance concept. If we declare a constructor as static, then it can not be accessed by its subclasses and will belong to a class level only. The program will not be compiled and throw a compile-time error.
Can we declare constructor as final?
No, a constructor can’t be made final
. A final method cannot be overridden by any subclasses. As mentioned previously, the final modifier prevents a method from being modified in a subclass. The main intention of making a method final would be that the content of the method should not be changed by any outsider.
Can constructor be virtual?
Constructor can not be virtual
, because when constructor of a class is executed there is no vtable in the memory, means no virtual pointer defined yet.
Why constructor is private in Singleton?
In singleton class, we use private constructor
so that any target class could not instantiate our class directly by calling constructor
, however, the object of our singleton class is provided to the target class by calling a static method in which the logic to provide only one object of singleton class is written/ …
Is constructor public by default?
Class constructors are package-private by default
. Enum constructors are private by default. The only constructor that’s public by default is the implicit, no-arguments one.
How do you call a private constructor?
Class. getDeclaredConstructor()
can be used to obtain the constructor object for the private constructor of the class. The parameter for this method is a Class object array that contains the formal parameter types of the constructor.
Can we declare constructor as private in C++?
Typically, constructors have public accessibility so that code outside the class definition or inheritance hierarchy can create objects of the class. But
you can also declare a constructor as protected or private
. Constructors may be declared as inline , explicit , friend , or constexpr .
Can a constructor be overridden?
Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. But,
a constructor cannot be overridden
. If you try to write a super class’s constructor in the sub class compiler treats it as a method and expects a return type and generates a compile time error.
Can a constructor be called explicitly?
Yes, it is possible to call special member functions explicitly by the programmer
.
Can static methods be private?
Yes, we can have private methods or private static methods in an interface in Java 9
. We can use these methods to remove the code redundancy. Private methods can be useful or accessible only within that interface only. We can’t access or inherit private methods from one interface to another interface or class.
Can destructor be private?
Destructors with the access modifier as private are known as Private Destructors
. Whenever we want to prevent the destruction of an object, we can make the destructor private.
Can we declare constructor as abstract?
We can declare a constructor with no arguments in an abstract class
. It will override the default constructor, and any subclass creation will call it first in the construction chain.
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 constructor be void?
Note that the constructor name must match the class name, and
it cannot have a return type (like void )
. Also note that the constructor is called when the object is created.
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 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.
Why constructor is not abstract in Java?
But, a constructor in Java cannot be overridden therefore, there is no need of using the final keyword with the constructor. Since
you cannot override a constructor you cannot provide body to it if it is made abstract
. Therefore, you cannot use abstract keyword with the constructor.
Can a destructor be virtual?
Yes, it is possible to have a pure virtual destructor
. Pure virtual destructors are legal in standard C++ and one of the most important things to remember is that if a class contains a pure virtual destructor, it must provide a function body for the pure virtual destructor.
Can virtual function static?
A virtual function cannot be global or static
because, by definition, a virtual function is a member function of a base class and relies on a specific object to determine which implementation of the function is called.
Can we call virtual function from constructor?
You can call a virtual function in a constructor
, but be careful. It may not do what you expect. In a constructor, the virtual call mechanism is disabled because overriding from derived classes hasn’t yet happened. Objects are constructed from the base up, “base before derived”.
What happens if constructor is private?
A private constructor in Java is used in restricting object creation. It is a special instance constructor used in static member-only classes. If a constructor is declared as private, then
its objects are only accessible from within the declared class
. You cannot access its objects from outside the constructor class.
Can constructors be overloaded?
Constructors can be overloaded in a similar way as function overloading
. Overloaded constructors have the same name (name of the class) but the different number of arguments. Depending upon the number and type of arguments passed, the corresponding constructor is called.
Can constructor be public in Java?
Access specifiers/modifiers allowed with constructors
Modifiers public, protected and, private are allowed with constructors
. We can use a private constructor in a Java while creating a singleton class.
Can a class have no constructor?
Can constructors take arguments?
Parameterized Constructors:
It is possible to pass arguments to constructors
. Typically, these arguments help initialize an object when it is created. To create a parameterized constructor, simply add parameters to it the way you would to any other function.
How do you initialize a private constructor?
First, initiate a constructor as private. Then create a private static instance of this singleton class. Keep in mind to NOT instantiate it. Then, write a static method, which checks the static instance member for null and initiates the instance.
Can we create immutable class in Java?
Can constructor return a value?
No, constructor does not return any value
. While declaring a constructor you will not have anything like return type. In general, Constructor is implicitly called at the time of instantiation.
Can a constructor be private or protected in Java?
Modifiers
public, protected and, private are allowed with constructors
. We can use a private constructor in a Java while creating a singleton class.
What happens if constructor is defined as private or protected?
If a constructor is declared as private, then
its objects are only accessible from within the declared class
. You cannot access its objects from outside the constructor class.
Should the constructor be protected?
The reason for making the constructor protected, rather than private, is the same as for making any other method or field protected instead of private:
so that it can be inherited by children
.
