What is the main difference between interface and abstract class in Java?
Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior. Variables declared in a Java interface is by default final. An abstract class may contain non-final variables.
What is difference between abstract class and interface with real time example?
Abstract classes can have methods with implementation whereas interface provides absolute abstraction and can’t have any method implementations. Abstract classes can have constructors but interfaces can’t have constructors. Abstract class have all the features of a normal java class except that we can’t instantiate it.
Why interface is used instead of abstract class?
The short answer: An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.
What is difference between class and interface?
A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements. A class may contain abstract methods, concrete methods. An interface contains only abstract methods.
What is the use of interface?
You use an interface to define a protocol of behavior that can be implemented by any class anywhere in the class hierarchy. Interfaces are useful for the following: Capturing similarities among unrelated classes without artificially forcing a class relationship.
What are the advantages of interface?
Advantages of interfaces over abstract base classes
- Space efficiency.
- Compiler optimisation.
- Efficient multiple inheritance.
- Object creation efficiency.
- Forces a clean separation of interface and implementation.
- Not type intrusive.
- Objects can implement the same interface in different ways.
- Avoidance of heap allocations.
Where do we use abstract class?
An abstract class is a good choice if we are using the inheritance concept since it provides a common base class implementation to derived classes. An abstract class is also good if we want to declare non-public members. In an interface, all methods must be public.
Why would you use an abstract class?
An abstract class is used if you want to provide a common, implemented functionality among all the implementations of the component. Abstract classes will allow you to partially implement your class, whereas interfaces would have no implementation for any members whatsoever.
How do we declare an abstract class?
You create an abstract class by declaring at least one pure virtual member function. That’s a virtual function declared by using the pure specifier ( = 0 ) syntax. Classes derived from the abstract class must implement the pure virtual function or they, too, are abstract classes.
Can abstract class have constructors?
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.
Can abstract class have body?
Abstract methods cannot have body. Abstract class can have static fields and static method, like other classes. An abstract class cannot be declared as final.
Can an interface have a constructor?
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).
Can abstract class have private methods?
If a method of a class is private, you cannot access it outside the current class, not even from the child classes of it. But, incase of an abstract method, you cannot use it from the same class, you need to override it from subclass and use. Therefore, the abstract method cannot be private.
Which method Cannot be overridden?
A method declared final cannot be overridden. A method declared static cannot be overridden but can be re-declared. If a method cannot be inherited, then it cannot be overridden. A subclass within the same package as the instance’s superclass can override any superclass method that is not declared private or final.
Can an interface have an abstract method?
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). All constant values defined in an interface are implicitly public , static , and final .
Are methods abstract?
The class and all of its methods are abstract. An abstract class can have implemented methods but the class itself cannot be instantiated (useful for inheritance and following DRY).
Can an interface method have a body?
Interfaces are declared using the interface keyword, and may only contain method signature and constant declarations (variable declarations that are declared to be both static and final ). All methods of an Interface do not contain implementation (method bodies) as of all versions below Java 8.
Are all methods in an abstract class abstract?
Not all methods in an abstract class have to be abstract methods. An abstract class can have a mixture of abstract and non-abstract methods. Subclasses of an abstract class must implement (override) all abstract methods of its abstract superclass.