combination of access & non-access modifiers for a class

[siva prakash]

Hi All,

I am reading K&B book, page :15, and tried following combinations and getting compilation error, Can any one explain me what could be logic for it.

1) private & protected with "final" modifier
2) private & protected with "strictfp" modifier
3) private & protected with "abstract" modifier , i can understand the combination of private & abstract showing compilation error.

Thanks inadvance,
Prakash.

[Antonio Tercero]

It depends:

final modifier means that you can't change the value of a variable member , and with methods it means that you can't override it so all access modifiers(private , protected, public ..) can be used with final.

abstract modifier means that the method is not implemented.
You can declare an abstract method in an abstract class or an interface.
In an abstract class, you can only apply protected, public or "Default" access modifers: you CAN'T apply private modifier because the first non-abstract method that extends the abstract class doesn't inherits private methods.

Example:

public abstract class MyAbstractClass {
 private final int count=1; // OK
 public abstract void f1(); // OK
 abstract void f2(); // OK
 protected  abstract void f3(); // OK
 private abstract void f4(); // COMPILATION ERROR:  subclasses can't  
                             // implement this method
}
 
class Test extends MyAbstractClass{
public void f1(){System.out.println("f1");}
void f2(){System.out.println("f2");}
protected void f3(){System.out.println("f3");}
}

In an interface, all methods declared are by default public and abstract, so you can only use public with abstract.

Finally, a method can't be final and abstract at the same time
final -> can't override the method
abstract -> you must override the method