This question already has answers here:
Why is there no multiple inheritance in Java, but implementing multiple interfaces is allowed?
(21 answers)
Closed 7 years ago.
In java by default all classes are inherit from Object class and even we can also inherit the classes.
class A{ // default **Object class** is extended
}
class B extends A{
//default **Object class** is extended and also **class A** extended.
}
Then why we say that java doesn't support multiple inheritance through classes?
It is just to remove ambiguity, because multiple inheritance can cause
ambiguity in few scenarios. One of the most common scenario is Diamond
problem.
Look at this page : http://www.instanceofjava.com/2014/12/why-java-does-not-supports-multiple.html
Related
This question already has answers here:
Java Multiple Inheritance
(17 answers)
Closed 2 years ago.
Please explain how to extend two classes from different packages.
public class Animal extends Herbivores extends Omnivores {
}
Multiple Inheritance or Diamond Inheritance is a feature of object oriented concept, where a class can inherit properties of more than one parent class.
Java does not support that.
There are multiple resources over the net which tells you the problem that arises if you are allowed to do that.
Coming to your problem, it seems to me like a fault in Design.
Animal should be a parent type rather than a child type. Both Herbivores and Omnivores are animals. Whereas an animal doen't necessary have to be either. It can be a carnivore also.
This question already has answers here:
Protected in Interfaces
(15 answers)
Closed 6 years ago.
Why does java force interface methods to be public and how does abstract class differs from an interface?
A quick response is:
All the interface methods must be overriden, for that they must be public.
Abstract classes can be extended by other classes, the interfaces only can be implemented by classes and inherited by other interfaces.
You can get a lot more information here: http://www.javaworld.com/article/2077421/learn-java/abstract-classes-vs-interfaces.html
This question already has answers here:
Do/can abstract classes replace interfaces? [duplicate]
(11 answers)
what is the actual use of interface in java? [duplicate]
(6 answers)
Closed 7 years ago.
In java there is interface which having only abstract method means method declration only and those methods are implement in class that implement interface so why to use interface which has only declaration .This question is asked in interview.
Interfaces are used for only declaration of methods because it can achieve multiple behavior. It is the class's responsibility to implement the interfaces and define their methods as they desire.
Interfaces allow same methods to be implemented in different manner by implementing classes, which allows you to achieve behavioral facility.
For understanding sake, you can consider interfaces exist so you can achieve behavioral approach for your application, and class exist to achieve characteristic approach.
This question already has answers here:
Defining an abstract class without any abstract methods
(12 answers)
Use of an abstract class without any abstract methods
(7 answers)
Closed 9 years ago.
can any one please explain the scenario when A class may be declared abstract even if it has no abstract methods. i have tried in many websites but i did not found it.Thanks a lot.
Broadly, this would be because the class provides concrete implementations of functionality but should not itself be instantiated. For example, an AbstractWidget in a price calculator may not be suitable to directly instantiate, but it has concrete implementations of certain widget functionality like being rearranged. The expectation is that the subclass adds new methods altogether, or overrides the ones already declared.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Interface vs Abstract Class (general OO)
When to use abstract class or interface?
Can you provided implementations on a abstract class?
what's the difference between these two?
and when will I know when will I know to use them?
This pages gives a good comparison: http://download.oracle.com/javase/tutorial/java/IandI/abstract.html . You could have found it with a very quick google search.
Interface is used for defining a contract. Abstract classes are used for defining some methods which are common to all descendants and possibly some methods which will differ(they will be abstract). With interfaces or abstract classes polymorphism is reached.