Ques) Can we access the non-final local variable inside the local inner class? 
Ans:  No
Ques) Can we define an interface within the class?

Ans:  Yes.
class A{ 
  interface Message{ 
   void msg(); 
  } 
} 
 
class TestNestedInterface2 implements A.Message{ 
 public void msg(){System.out.println("Hello nested interface");} 
 
 public static void main(String args[]){ 
  A.Message message=new TestNestedInterface2();//upcasting here 
  message.msg(); 
 } 
} 
Ques) Can we define a class within the interface?
Ans:  Yes. If we define a class inside the interface, java compiler creates a static nested class.
To provide default implementation of an interface we can define a class inside an interface
Interface
public interface VehicleService {
public void repair();
public class DefaultVehicle implements VehicleService{
    @Override
    public void repair() {         
        System.out.println(" Default Repair");
    }
}
public class busRepair implements VehicleService{
   @Override
   public void repair() {
       System.out.println(" Bus Repair");
   }
   public static void main(String args[]){
        busRepair b = new busRepair();
        b.repair();
        DefaultVehicle d = new DefaultVehicle();
        d.repair();
    }
 }

Java Anonymous Implementer of an Interface Type

 

interface Manageable
{
  public void manage();
}
 
public class AnonymousInterfaceDemo
{
  public static void main(String[] args)
  {
    Manageable m = new Manageable() {
      public void manage()
      {
        System.out.println("It is manageable");
      }                   
    }; // anonymous interface implementer closes here
    //m contains an object of anonymous interface implementer of Manageable.
    m.manage();
  }
}

Java Anonymous Inner Class in Method Arguments

interface Manageable
{
  public void manage();
}
 
class Manager
{
  public void canManage(Manageable m)
  {
         m.manage();
  }
}
public class MethodArgumentAnonymousClassDemo
{
  public static void main(String[] args)
  {
    Manager m = new Manager();
    m.canManage (new Manageable ()         
         {
      public void manage()
      {
        System.out.println("Yes, it is being anonymously managed!");
      }                   
    }); // anonymous interface implementer as method argument closes here
  }
}

Java doesn't have a diamond problem since interfaces don't contain code.


A typical problem in OO programming is the diamond problem. I have parent class A with two sub-classes B and C. A has an abstract method, B and C implement it. Now I have a sub-class D, that inherits of B and C. The diamond problem is now, what implementation shall D use, the one of B or the one of C?

Java knows no diamond problem. I can only have multiple inheritance with interfaces and since they have no implementation, I have no diamond problem. Is this really true?
yes, because you control the implementation of the interface in class. 

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