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Can we create objects for interface?
We can’t create instance(interface can’t be instantiated) of interface but we can make reference of it that refers to the Object of its implementing class. A class that implements interface must implements all the methods in interface. All the methods are public and abstract.
Can an interface implement another interface?
An interface can extend any number of interfaces but one interface cannot implement another interface, because if any interface is implemented then its methods must be defined and interface never has the definition of any method.
Can we declare fields in interface?
Since Java 1.8, an interface can have default methods and static methods as well. An interface can have default methods and static methods. Any other methods are implicitly public and abstract. All the fields declared in an interface are implicitly public, static and final constants.
Why interface Cannot have fields?
The interface will always defined with the help of keyword ‘interface’. Interface cannot contain fields because they represent a particular implementation of data. Multiple inheritance is possible with the help of Interfaces but not with classes.
Can I Autowire interface in spring boot?
currently we only autowire classes that are not interfaces. Another part of this question is about using a class in a Junit class inside a Spring boot project. If we want to use a CalendarUtil for example, if we autowire CalendarUtil, it will throw a null pointer exception.
Do you need to use field injection in Java?
First of all, you have to answer a question: Do I want my class to be instantiable only with reflection? Using field injections means narrowing down compatibility of a class to dependency injection environments that instantiate objects using reflection and support these particular injection annotations.
How is constructor injection different from field injection?
At least with constructor and setter injection, you have the option of not using the frameworks and/or reflection in your tests. Well, this seems a polemic discussion. The first thing that needs to be addressed is that Field injection is different from Setter injection.
What does interface injection mean in Java Spring?
I think, that the confusion around interface injection is caused by missunderstanding what the term “interface injection” actually means. In my understanding, interface injection describes the ability of a bean contener to inject a new interface to the bean, no matter that the class definition of this bean is not implementing it.
Can a bean be injected into an interface?
The fact, that in all cases bean is injected into a field defined as an interface does not matter- all operations are done with beans created out of concrete instances. As you see here, it is even possible to create a bean out of interface! Still, it is not a interface injection, as IoC contener initializes instanse of this bean by its own.