Should constructor be protected?
Protecting a constructor prevents the users from creating the instance of the class, outside the package. During overriding, when a variable or method is protected, it can be overridden to other subclass using either a public or protected modifier only. Outer class and interface cannot be protected.
Should constructors be public or private?
A constructor is a special member function of a class which initializes objects of a class. In C++, constructor is automatically called when object of a class is created. By default, constructors are defined in public section of class.
Can a constructor be protected 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 .
Why should constructors 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.
Can we have 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.
When should I use protected in Java?
Use the protected modifier when you need to only allow access to the code within the package or when its subclassed.
What happens if I make a constructor 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.
Why do we generally declare constructor as public members?
The public constructor also means it can be accessible outside the class The other class can also getting them in a simply manner however if we make the constructor as private it is not accessible outside the class. Also we make constructor the constructor as public to initialized the class any where in the program .
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 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.
Why constructors are not inherited?
In simple words, a constructor cannot be inherited, since in subclasses it has a different name (the name of the subclass). Methods, instead, are inherited with “the same name” and can be used.
Can constructor be static?
Java constructor can not be static
One of the important property of java constructor is that it can not be static. We know static keyword belongs to a class rather than the object of a class. A constructor is called when an object of a class is created, so no use of the static constructor.
Can we declare constructor as final?
No, a constructor can’t be made final. A final method cannot be overridden by any subclasses.
Can abstract class have constructor?
Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses.
Can inner class be protected?
You can just think protected inner class is protected member, so it only access for class, package, subclass but not for the world. In addition, for outter class, there is only two access modifier for it. Just public and package.
Can constructor throw an exception?
Yes, constructors are allowed to throw an exception in Java. A Constructor is a special type of a method that is used to initialize the object and it is used to create an object of a class using the new keyword, where an object is also known as an Instance of a class.
Can copy constructor be private?
As you can see, in the Derived type, the copy constructor was intentionally made private, because it would be bad API design to give programmers to ability to accidentally try to call the copy constructor manually, rather than using the clever interface provided by clone().
Can we extend a class with private constructor?
When you have a class with only private constructors, you can also change the class to final because it can’t be extended at all.
How many constructor can a class have?
You can have 65535 constructors in a class(According to Oracle docs).
Do constructors have a return type?
No, constructor does not have any return type in Java. Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. Mostly it is used to instantiate the instance variables of a class.
Which two statements are not true about constructors?
Which two statements are NOT true about constructors? A constructor method has a return type void. A constructor method may return a value.
Which of the following is not true about constructors?
Constructor needs to be invoked explicitly: There is no need to call constructors directly because they are called automatically when the object is created. This is a false statement.
Can singleton class have multiple constructors?
EDIT: IF you have a singleton-class you won´t need both constructor. All your initializations can be done by the default one, where you set all important members of that instance whereas the static one can be omitted.
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.
Can we call constructor without creating object?
NO. You can’t invoke a constructor without creating an object.
Can you have 2 constructors in Java?
The technique of having two (or more) constructors in a class is known as constructor overloading. A class can have multiple constructors that differ in the number and/or type of their parameters. It’s not, however, possible to have two constructors with the exact same parameters.
Does a singleton class need a constructor?
So for a Singleton class, i.e. one with at most one instance, then a private constructor is required.
Can we overload private constructor in Java?
1) NO! A constructor belongs to the class in which it is declared. A sub class is a different class and must have its own constructor. So, constructors simply can’t be overridden.
Does a base class need a default constructor?
The default constructor in the Person class is not inherited by Employee and therefore a default constructor must be provided in Employee, either automatically by the compiler or coded by the developer. Note that the compiler will also generate a call to the base class default constructor.
Do inherited classes need constructors?
To inherit only selected ones you need to write the individual constructors manually and call the base constructor as needed from them. Historically constructors could not be inherited in the C++03 standard.
Can we declare interface as final?
interface method can not be final . cannot be declared final.
What is difference between constructor and method?
Constructor is used to create and initialize an Object . Method is used to execute certain statements. A constructor is invoked implicitly by the System. A method is to be invoked during program code.
Can constructor be overloaded in derived class?
Since the constructors can’t be defined in derived class, it can’t be overloaded too, in derived class.
Can you use this () and super () both in a constructor?
“this()” and “super()” cannot be used inside the same constructor, as both cannot be executed at once (both cannot be the first statement). “this” can be passed as an argument in the method and constructor calls.
Can we declare a class as static?
We can declare a class static by using the static keyword. A class can be declared static only if it is a nested class. It does not require any reference of the outer class. The property of the static class is that it does not allows us to access the non-static members of the outer class.
Can abstract class be inherited?
An abstract class cannot be inherited by structures. It can contain constructors or destructors. It can implement functions with non-Abstract methods. It cannot support multiple inheritances.
Can we pass parameter in abstract class?
Even though A is abstract, you can receive parameters of type A (which, in this case, would be objects of type B ). You cannot really pass an object of class A , though, since A is abstract and cannot be instantiated.
What happens if a constructor is declared protected?
Protecting a constructor prevents the users from creating the instance of the class, outside the package. During overriding, when a variable or method is protected, it can be overridden to other subclass using either a public or protected modifier only. Outer class and interface cannot be protected.
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 outer class default?
Java inner class is defined inside the body of another class. Java inner class can be declared private, public, protected, or with default access whereas an outer class can have only public or default access.
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.
When should I use protected in Java?
Use the protected modifier when you need to only allow access to the code within the package or when its subclassed.
Can constructor be static?
Java constructor can not be static
One of the important property of java constructor is that it can not be static. We know static keyword belongs to a class rather than the object of a class. A constructor is called when an object of a class is created, so no use of the static constructor.
Can 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 constructor have try catch?
Like any method can throw exception, a constructor can also throw a exception since it is also a method which is invoked when a object is created. yes we can write a try catch block within a constructor same as we can write in inside a method.
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.
What is a static constructor?
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 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.