What is the point of Interfaces?

What is the point of Interfaces? From my understanding, it is basically a list of abstract methods. These methods then can be used by implementing the class. Like so in shorthand:

public interface whatever
{
public void joe();
}
public class steve implements whatever
{
public void joe()
{
body
}
public static void main(String args[])
{
joe();
}
}

So in other words, you going to end up declaring it either way.

An interface is kind of like a template or protocol. It provides a format that anything implementing it must follow. For example, when Mr X comes to work on your code, and he wants to create a new class A based on the system you've defined in interface B, he can just implement A from B and knows what functions he has to add.

This may help you: Interface (Java) - Wikipedia, the free encyclopedia

Ok, so it is more of a template. So there is no real ease in coding, like a method, but more of ease for conformity.

Correct. You have to override all its methods anyway. It's just a way of making the code fit to what was originally intended.

They mean that you can hide implementation details.

Take the Connection interface for JDBC (database access stuff of Java). This is an interface that simply defines what all Connection classes need to be able to do (or mostly do anyway). Each db vendor has its own version of this for interacting with their database, but the Java code does not need to know how that works, it just needs to know it can get a connection and create Statements.

Now, it also means that you can change the database at the backend (say from MySQL to Derby or Oracle) and not have to change the main Java code, assuming your db set up data is in a properties file of some sort anyway.

have a look at this

Code:

---

public interface Card
{
public Image getCardImage();
}




public class PokerCard implements Card
{
public Image getCardImage()
{
// code here
}


// another implementation
public class MonopolyCard implements Card
{
public Image getCardImage()
{
// code here
}

---

See you got one interface but you can implement it any way you want

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Interfaces are really useful in a case such that you don't want to inherit classes from unrelated classes, to invoke the required functionality.

For an example assume that you've a class name vehicle with a method fuleType(). It's ridiculous that food class inherit that class just because it has fuelType() method, which is no relevant at all. If you define it in an interface then you can implement in accordingly.

The real power of interfaces comes into play when discussing terms such as modularity and encapsulation. The basic premise is, if class A needs class B to do something, class A doesn't have to know how class B performs the operation, just that it does it. Also, consider the following example:

Code:

---

public void doSomething(Vector v) {
  //code
}

---

Later on, you decide to use ArrayLists instead of Vectors, and now you have a whole bunch of code to correct. How to avoid it? Interfaces:

Code:

---

public void doSomething(List l) {
  //code
}

---

List is an interface, and now this method will work with any class that implements the List interface, making design changes much easier.

Quite similar thing I've explained in my last post I guess. ;)