Multiple Inheritance

[tarun saha]

hi guys,

I have read many docs regarding multiple inheritance in java.

I know that in java one class can extend only one class but can implement many interfaces, but still my doubt remains unclear.

If i have 3 classes

public class MyClassA{
}

public class MyClassB{
}

public class MyClassC{
}

how can inherit the properties of the 3 classes. I read that multiple interfaces can be implemented. But interface cannot extend a class. So how will interface use the properties of class?

Lets say that my main intented class is

public class AllClassProperties which will have certain selected properties same as the three( i am not saying common properties, it is only selected properties and their methods)

how can i bridge between AllClassProperties and the three myclasses?

CAN WE USE INTERFACE INSIDE A CLASS?

please help me with a complete example or a link if you can...

thanks for any help in advance.

[Istvan Kovacs]

You could create interfaces for each of those classes (InterfaceA for MyClassA etc.), and have

public class MyClassA implements InterfaceA {...}
public class MyClassB implements InterfaceB {...}
public class MyClassC implements InterfaceC {...}

public class AllClassProperties implements InterfaceA, InterfaceB, InterfaceC
{
  // member variables should/could actually be interface types
  private MyClassA myA = new MyClassA();
  private MyClassB myA = new MyClassB();
  private MyClassC myC = new MyClassC();

  // this method is defined in InterfaceA
  public String performSomeOperationDefinedOnA() {
    return myA.performSomeOperationDefinedOnA();
  }
  // etc.
}

Eclipse has support for delegation (Source -> Generate Delegate Methods).

If you search for composition inheritance, you'll find many articles, e.g.
http://www.artima.com/lejava/articles/designprinciples4.html

[tarun saha]

hmm, i'l try it out.

[Istvan Kovacs]

tarun saha wrote:hmm, i'l try it out.

In general, try not to create classes that are overcomplicated. Implementing several interfaces will bring lots of public functions; the delegate methods will mean lots of code (even though generated). Check whether you can simplify the design, whether there's no way to avoid this class taking on so much functionality/responsibility.