What is advantage of interface in java?Plz help

Please explain in dumbest language possible.So i can understand
check this example

Code:

---

interface BaseInterface
 {
    int i=0;
 }
interface BaseInterface2
 {
    int i=1;
 }
class SubClass implements BaseInterface,BaseInterface2
 {
    public static void main(String args[])
    {
        System.out.println(BaseInterface2.i);
    }
 }

---

it works fine

just it is used to define some general information which can be used for specific purpose as we can define an interface Vechile with some attributes and method as drive(). Now this interface can be implemepented by some another classes as Car, Bus. now these classes define their own way to how to drive them. Isn't a sufficient

In your example there are two interfaces and a class with the main method.

An interface is a collection of method definitions, empty bodies, and constant values. So you cannot modify those variable values later in your application.

Interface form a relationship between the Java class and the outside world. This relationship validate in compile time. So if a class implement and interface, all the methods of that interface must be coded before compile.

In your case there is no any methods to implement in the interface implemented class. Only have variable, constant variables.

If you want to read about more, go the the Suns' tutorial. There are nice explanation on this. Good luck!

ty for replies
Is not the problem of ambiguity still there??
i actually expect answer likes problems faced without interface and thus solved by using them.

Quote:

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i actually expect answer likes problems faced without interface and thus solved by using them.

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I don't see how these explanations would have any bearing on your examples as they're not good examples of the beneficial use of interfaces. Probably better than our trying to rewrite a chapter for ya (especially since your question is so general and broad), I'd recommend you read some good tutorials on interfaces and then come back if you have any specific questions. A decent place to start is here: Sun Interface Tutorial

Best of luck!

edit: one more tutorial that's somewhat simplistic but briefer than the one above: Game programming Wiki: Java: Tutorials: Interfaces
I still recommend the first link as the more complete tutorial, but I'd recommend that you read it second.

Interfaces are used to allow a group of classes to say they implement a certain set of methods. Another class can then declare a field of the interface type and use the methods of any of the classes that implement that interface.

This is more useful for advanced programming; you certainly can write applications without creating interfaces.

Basic use of interface
Suppose you have three classes Ferrari, Toyota and Ford. All these are Cars and can move().

Code:

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Ferrari scaglietti = new Ferrari();
Toyota yaris = new Toyota();
Ford focus = new Focus();

---

If you wanted to call move() for all 3 objects you should code like this:

Code:

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yaris.move();
scaglietti.move();
focus.move();

---

But if you had 1 thousand of cars it would be impossible. So you say

Code:

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interface Car {
  void move();
}

class Ferrari implements Car { ... public void move() ... }
class Toyota implements Car { ... public void move() ... }
class Ford implements Car { ... public void move() ... }

---

And then you can:

Code:

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Car[] myCars = { ... }

for(each car in myCars) {
  car.move();
}

---

It is called an UPCAST. This is one of the major goals of interfaces. Of course, there are lots of other things, you'd better read the Sun Tutorial linked by Fubarable

The main use of interface is to inherit multiple inheritence.
i think you are beginner of java.
i hope you know java does'nt support multiple inheritence,to overcome this ,interface is used often.

Quote:

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Originally Posted by makpandian

The main use of interface is to inherit multiple inheritence.

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And I disagree with this strongly. I believe that the main use of interface is to loosen coupling between a public contract and the private implementation of the contract.

contract thing sounds convincing, as(i think) there was no such mechanism in c++ i.e interface.
However most website said multiple inheritance as advantage.So i actually thought that interfaces remove disadvantage of multiple inheritance i.e ambiguity(which is what my example, in earlier post, is)...HOwever this advantage (i think) is only for java not having multiple inheritance with classes.
I have already visited that sun interface tutorial but with "Multiple Inheritance Disadvantage in Mind" and neglected others.
And Sorry guys i'm pretty poor at grasping things and thnks for your replies.

If i'm wrong please correct me.

Eyeinstyin's last post has the right information; let me try to clarify a bit.

Java was designed to be a "better" C++. C++ allows you extend multiple classes. This is powerful, but it can lead to problems. The Java designers decided to allow only one class to be extended. To make up for that, they created interfaces. A Java class extends one class and can implement many interfaces. Interfaces do serve as contracts, guaranteeing that the class specifies all the specified methods.

I dont say that interface are used only for an alternative of multiple inheritance .
What i said is ,one of the usage of interface is an alternative of multiple inheritance...

I agree with fubarable that interface are being used for loose coupling..

Any by interface we can force a class that should do certain things..

Thanks Fubarable..

Hi

What would you do when someone asks you to buy 10 things or more than that which you can not hold it by your hands , certainely you will take help of some bag by which you will not worried about to hold 10+ things by your hand , now you just need to hold only that bag.

Now think about a situation when your friend suddenly come to your home and ask 5-6 things from that bag and you say yes i have those and i can give it to you but the condition is if you want 5-6 things you also need to carry other things too which ppl called contract which you must need to follow.

Please let me know how much i m correct to tell you about interface.

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