Should I put constructor in interface?
In order to call any method we need an object since there is no need to have object of interface, there is no need of having constructor in interface (Constructor is being called during creation of object).
Can we declare constructor inside interface and abstract class?
Yes, an Abstract Class can have a Constructor. You Can Overload as many Constructor as you want in an Abstract Class. These Contractors Can be used to Initialized the initial state of the Objects Extending the Abstract Class.
What happens when a constructor is defined for an interface?
What happens when a constructor is defined for an interface? Explanation: Constructor is not provided by interface as objects cannot be instantiated.
Can an interface contain a constructor Java?
Interfaces can contain instance methods, properties, events, indexers, or any combination of those four member types. Interfaces may contain static constructors, fields, constants, or operators.
Why constructor is not used in interface?
Constructor in an interface An Interface in Java doesn't have a constructor because all data members in interfaces are public static final by default, they are constants (assign the values at the time of declaration). There are no data members in an interface to initialize them through the constructor.
Can we call constructor of abstract class?
The constructor inside the abstract class can only be called during constructor chaining i.e. when we create an instance of sub-classes. This is also one of the reasons abstract class can have a constructor.
Why constructor is not overridden?
Constructor Overriding is never possible in Java. This is because, Constructor looks like a method but name should be as class name and no return value. Overriding means what we have declared in Super class, that exactly we have to declare in Sub class it is called Overriding.
Can a class have multiple interfaces?
A class can implement more than one interface at a time. A class can extend only one class, but implement many interfaces. An interface can extend another interface, in a similar way as a class can extend another class.
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.
Can we declare interface as abstract?
The interface body can contain abstract methods, default methods, and static methods. An abstract method within an interface is followed by a semicolon, but no braces (an abstract method does not contain an implementation).
Can we declare variable in interface?
No you can not declare variable in interface. No, we can't declare variables, constructors, properties, and methods in the interface. no,interface cannot contains fields.
Can we define class inside interface Java?
Yes, you can define a class inside an interface. In general, if the methods of the interface use this class and if we are not using it anywhere else we will declare a class within an interface.
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.
Can we use constructor in inheritance?
No, constructors cannot be inherited in Java. In inheritance sub class inherits the members of a super class except constructors. In other words, constructors cannot be inherited in Java therefore, there is no need to write final before constructors.
Can we create constructor in static class?
Static classes cannot contain an instance constructor. However, they can contain a static constructor. Non-static classes should also define a static constructor if the class contains static members that require non-trivial initialization.
Why can't we define constructors in interfaces?
This is because interfaces do not allow to define the method body in it.but we should have to define the constructor in the same class as interfaces have by default abstract modifier for all the methods to define. That's why we can not define constructor in the interfaces.
Why can't we create objects to declared methods?
Why we can’t create object to declared methods is-object creation is nothing but allocating some memory (in heap memory) for non-static members . JVM will create memory for members which are fully developed and ready to use.Based on those members , JVM calculates how much of memory required for them and creates memory.
What is an interface in API?
An interface defines a contract for an API, that is a set of methods that both implementer and user of the API agree upon. An interface does not have an instanced implementation, hence no constructor. The use case you describe is akin to an abstract class in which the constructor calls a method of an abstract method which is implemented in an child ...
What is a use case in a class?
The use case you describe is akin to an abstract class in which the constructor calls a method of an abstract method which is implemented in an child class.
What is dependencies in interfaces?
Dependencies that are not referenced in an interfaces methods should be regarded as implementation details, not something that the interface enforces. Of course there can be exceptions, but as a rule, you should define your interface as what the behavior is expected to be.
Can you ensure that every implementation of this class has a receiver set?
You say "In the constructor I could ensure [every implementation of this class really has an receiver set]." But no, you couldn't possibly do that. Provided it was possible to define such a constructor, the parameter would only be a strong hint to your implementors – but they could chose to simply ignore it if they wanted to.
Can constructors be used inside an interface?
without object creation, there is no chance to initialize non-static members through a constructor.That is why constructor is not allowed inside a interface.(as there is no use of constructor inside a interface)
How to declare an interface?
To declare an interface, use interface keyword. It is used to provide total abstraction. That means all the methods in interface are declared with empty body and are public and all fields are public, static and final by default. A class that implement interface must implement all the methods declared in the interface. To implement interface use implements keyword.
Why should constructor not be static?
Another good point mentioned by Prashanth in the comment section: Constructor definition should not be static because constructor will be called each and every time when object is created. If you made constructor as static then the constructor will be called before object creation same like main method.
What is constructor's main use?
Constructor's main use is to actually initialize the variable that we declare for the class , but the thing is , for interface every variable is public static final variable , thus what i mean to say is , every variable in interface is supposed to be initialized by us while declaring and it is final , and we cant modify value of final variable .
What is interface in programming?
Interface is a promise to calling code of methods that will exist on any object that conforms. It is not specific to any single class; it isolates the caller from that
Why do we use interfaces in abstract classes?
So the question arises why use interfaces when we have abstract classes?The reason is, abstract classes may contain non-final variables, whereas variables in interface are final, public and static.
Is a constructor allowed in an interface?
To call any method, object is needed and for interface no object is required. Hence, no constructor is allowed in interface.
Is there a default constructor in Java 8?
While it is true that since Java 8, one can have a default method, there is no such thing as a default constructor, nor will there be.
What happens if both interfaces have a constructor?
In such a case, if both interfaces would include a constructor, they would dictate incompatible signatures for your class. You would not be able to write a constructor that would work with both, except in the rare case where their constructor is identical.
Why is my interface so many methods?
If the interface contains too many methods, this probably points to a design issue where your interface just mirrors your classes. This might lead to code where different responsibilities are so tightly coupled that you can’t make changes to one without affecting the other.
What does the interface care about?
So, the interface does only and exclusively care about the interaction points between objects. The instantiation (which is the constructor’s responsibility) is not about how objects interact, but rather about how to turn a class (blueprint) into an object in the first place. At the point where the constructor comes into play, you don’t even have an object yet.
Why do we use interfaces?
The goal of using interfaces is to make your code agnostic of specific implementations. Whenever you want to call a method declared in an interface, you can just rely on the object implementing the interface to accept that method call.
Can constructors be used in interfaces?
Don’t put constructors into your interface definitions. They don’t serve a valid purpose, and they might cause all sorts of issues down the road.
Do you need to know if a view object has a logger?
If you get passed a View object, and you want to render that view, you should not need to know whether that specific object had also asked for a Logger when being instantiated.
Do you need a signature for API?
If you absolutely must provide a specific signature to be used as part of your API, you are already defining one part of the specific implementation, not just the contract.
