- 1 What is the point of a default constructor?
- 2 Is it mandatory to use constructor in a class?
- 3 Does every interface have a default constructor?
- 4 Which class has a default constructor?
- 5 Can we inherit a constructor?
- 6 Are default constructors inherited?
- 7 Why can’t a constructor be final?
- 8 Why constructor has no return type?
- 9 Can a constructor be private?
- 10 Can an interface have main method?
- 11 Can we declare an interface as final?
- 12 Can an interface be instantiated?
- 13 What is default constructor with example?
- 14 How many arguments does a default constructor have?
- 15 How many default constructors can a class have?
What is the point of a default constructor?
If not Java compiler provides a no-argument, default constructor on your behalf. This is a constructor initializes the variables of the class with their respective default values (i.e. null for objects, 0.0 for float and double, false for boolean, 0 for byte, short, int and, long).
Is it mandatory to use constructor in a class?
CONSTRUCTOR is a special method that is used to initialize a newly created object and is called just after the memory is allocated for the object. … It is not mandatory for the coder to write a constructor for a class.
Does every interface have a default 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.
Which class has a default constructor?
Java compiler automatically creates a default constructor (Constructor with no arguments) in case no constructor is present in the java class.
Can we inherit a constructor?
Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass.
Are default constructors inherited?
Constructors are not inherited.
The default constructor just invokes the default constructor of the superclass, and the default constructor of Object is empty.
Why can’t a constructor be final?
The child class inherits all the members of the superclass except the constructors. In other words, constructors cannot be inherited in Java therefore you cannot override constructors. So, writing final before constructors makes no sense. Therefore, java does not allow final keyword before a constructor.
Why constructor has no return type?
So the reason the constructor doesn’t return a value is because it’s not called directly by your code, it’s called by the memory allocation and object initialization code in the runtime. Its return value (if it actually has one when compiled down to machine code) is opaque to the user — therefore, you can’t specify it.
Can a constructor be private?
Yes, class can have a private constructor. It is needed as to disallow to access the constructor from other classes and remain it accessible within defined class. … A singleton is a design pattern that allows only one instance of your class to be created, and this can be accomplished by using a private constructor.
Can an interface have main method?
main() is a static method. Hence, main() is allowed in interfaces. We don’t need this, since it wasn’t allowed before, and yet we survived. But since static methods, by definition, are not bound to an instance of a class, but to the class itself, it makes sense to allow them in interfaces.
Can we declare an interface as final?
If you make an interface final, you cannot implement its methods which defies the very purpose of the interfaces. Therefore, you cannot make an interface final in Java. Still if you try to do so, a compile time exception is generated saying “illegal combination of modifiers − interface and final”.
Can an interface be instantiated?
Interfaces cannot be instantiated, but rather are implemented. A class that implements an interface must implement all of the non-default methods described in the interface, or be an abstract class.
What is default constructor with example?
In computer programming languages, the term default constructor can refer to a constructor that is automatically generated by the compiler in the absence of any programmer-defined constructors (e.g. in Java), and is usually a nullary constructor.
How many arguments does a default constructor have?
Types of constructor
There are two type of constructor in Java: No-argument constructor: A constructor that has no parameter is known as default constructor. If we don’t define a constructor in a class, then compiler creates default constructor(with no arguments) for the class.
How many default constructors can a class have?
A class can only have one default constructor.