This question already has answers here:
Implementing Class Adapter Pattern in Java
(5 answers)
Closed 9 years ago.
Is it possible to implement class adapter pattern in Java?
I'm trying to read everything on the internet but still have found an example.
It is possible, but pure interfaces must be used instead of abstract classes, since Java does not support multiple inheritance.
There are two variations of the Adapter pattern: inheritance-based (a.k.a. class Adapter) and composition-based. The inheritance variation requires the use of multiple inheritance, which doesn't exist in Java and therefore it's impossible to implement. But of course, you can do the composition-based implementation, without any problems.
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This question already has answers here:
Why is there no multiple inheritance in Java, but implementing multiple interfaces is allowed?
(21 answers)
Closed 3 years ago.
Multiple inheritance is not supported in the case of class because of ambiguity. However, it is supported in case of an interface. why there is no ambiguity when it comes to implementation?
Its because interface just states what methods are there. We need to define how methods will work.
And even if you define a method it automatically becomes static(from java 1.8 on wards. defining method body is permitted in an interface).
In multiple inheritance, same function may be defined differently in both the parent class which results in conflict. Thus, Multiple inheritance is not supported.
This question already has answers here:
Marker Interfaces in Java?
(10 answers)
Closed 3 years ago.
I just need some clarifications regarding marker interface in java. I have read that its an empty interface in java. I just want to know why and where we need to use this. Can anyone please help.
Shortly said, it is used to mark (or annotate) types with some information that the JVM compiler will use. For instance, the Serializable is a marker interfaces that a type must implement if it needs to have its state persisted (serialized and deserialized).
This question already has answers here:
What does it mean to "program to an interface"?
(33 answers)
Closed 6 years ago.
I can't understand a simple thing.
example: A is an interface, B is a class that implement correctly A.
What dose exactly mean doing:
A name = new B(some_argument);
I see lot of people using this instead of
B name = new B(some_argument);
But I can't figure out what dose that mean making an object with an interface.
And WHY they do this? There are some differences between them?
Sometimes one is better than other?
for example the opposite dose not work
B name = new A();
technically both works.
The reason most people use the first solution (and you should do that too) is that an interface defines a certain contract / API for a type of classes.
That means an interface is used when you dont know the implementation of it or the implementation is exchangeable.
So coding against the interface and not against the real specific implementation is the best way to make your code exchangeable and generic which helps you to modularize your code, keep hard-linked-dependency between classes as low as possible and make your code maintainable.
Also an interface can be used to add additional functionality to a class as you can implement multiple interface but only extend one class.
A practical example:
Think of an SDK for a plugin. It defines some interface.
How do you want to call a function of a class implementing this interface when the implementation of that interface is done by an other guy wrinting a plugin two years after you developed your application/sdk? ;)
This question already has answers here:
Why is multiple inheritance not supported in most of programming language?
(3 answers)
Closed 9 years ago.
Yeah the title pretty much describes the question.
Are there any advantages to non allowing multiple inheritance in a programming language?
It removes the possibility of the so called "diamond problem" (http://en.wikipedia.org/wiki/Multiple_inheritance#The_diamond_problem) that can occur when a class inherits from two classes having different implementations of methods of the same name.
Java instead have interfaces. A class can implement any number of interfaces and you can use a reference of the interface type to refer to any object of a class that implements this interface. Interfaces does not contain implementations and cannot be instantiated.
This question already has answers here:
Closed 12 years ago.
I have a class which inherits from two different interfaces. Both interfaces declare a method with the same name. How can I provide a different implementation for each interface ?
In C#, the answer is there, but it does not work in java:
Inheritance from multiple interfaces with the same method name
I thought about providing a union implementation which uses type comparison but it's kind of ugly.
Thanks
EDIT : closed, my question was a duplicate of the following, thank you for the answers !
Java - Method name collision in interface implementation
You can't. Interfaces describe behavior, but they don't implement it. So if you implement a method, there's no way to tell which interface you are implementing it from.
No, there's no equivalent feature in Java.
And you can't do it yourself, because inside the method, you have no way of telling if the calling code is referencing the object as InterfaceA or InterfaceB. Even if you could, I think it would be a bad idea.