an abstract class contains the concrete methods as well 
abstract methods. It may instance variables and static 
final variables
an interface contains only abstract methods. all the 
variables are by default static and final.
an abstract class contains constructor where as an 
interface does not have constructors...

abstract class A
{
protected abstract void show();
}

public class xx extends A
{
protected void show()
{
System.out.println("karthik ok");

}

static void main(String aa[])
{
xx ob=new xx();
ob.show();
}
}


But in Interface


interface A
{
protected abstract void show();
}



public class xx implements A
{
protected void show()
{
System.out.println("karthik ok");

}

static void main(String aa[])
{
xx ob=new xx();
ob.show();
}
}

modifier protected not allowed here
protected abstract void show(); in Interface
Because Default public method


But in Abstract class we can have protected


interface A
{
int x;//Error we should need initial value
}