Access modifiers

[Preety Narashimhan]

Hi folks,
List of doubts on Access Modifiers

1.Are there no protected classes?? Y not if “protected” signifies that it can be accessed/extended by the sub-classes.
2.Please give me a real example of static classes.
3.Is it possible to equate static methods with final methods??
4.Is it possible to sub-class a private class, when it is not even accessible?
5.Is void a datatype?
6.Consider the following eg:

public class SuperClassA{
protected int superClassVarA;
protected void superClassMethodA(){
System.out.println("In superClassMethodA method");
}
}
public class SubClassB extends SuperClassA{
SuperClassA objRefA = new SubClassB(); //1
SubClassB objRefB = new SubClassB(); //2
void subClassMethodB(){
objRefB.superClassMethodA(); //3
objRefA.superClassVarA; // 4
}
}
Here an object of the SuperClassA(objRefA) is referencing the object of the subclassB. Since the member variable “superClassVarA” is protected in the Superclass A, y is it not available to the SubclassB?
7. When a particular native method returns a class reference then how does java handle such a return value, when it does not even know the definition of hte class(the member variables and its methods)

[Anthony Villanueva]

1. You can have a protected inner class, if I understood you correctly...

public class Test46
{   
public static void main(String[] arg) 
{
new Sub().new Inner().print();
}
}
class Outer
{
protected class Inner
{
void print() { System.out.println("Inner"); }
}
}
 
class Sub extends Outer
{
}

[Anthony Villanueva]

2.

public class Test46
{   
public static void main(String[] arg) 
{
new Outer.StaticClass().print();
}
}
class Outer
{
static class StaticClass
{
void print() { System.out.println("Static"); }
}
}

[Anthony Villanueva]

3. Static methods and final methods are not equivalent.

public class Test46
{   
final public static void main(String[] arg) 
{
System.out.println("Final and Static");
print();
Test46 t = new Test46();
t.aMethod();
t.anotherMethod();
}
public static void print() { System.out.println("Not Final, Static"); }
public void aMethod()  { System.out.println("Not Final, Not Static"); }

public final void anotherMethod()  { System.out.println("Final, Not Static"); } 
}

[Anthony Villanueva]

4. I don't think I understand you here. If it's not accessible it wouldn't be visible, yes?
5. No

[Lance Finney]

Actually, Void is a datatype, if you're talking about the Void class. It doesn't do much, but it's used in reflection.

[Eureka Jana]

6.Try with this:
public class SuperClassA{
protected int superClassVarA;
protected void superClassMethodA(){
System.out.println("In superClassMethodA method");
}
}
public class SubClassB extends SuperClassA{
public void subClassMethodB(){
SuperClassA objRefA = new SubClassB(); //1
SubClassB objRefB = new SubClassB(); //2
objRefB.superClassMethodA(); //3
objRefA.superClassVarA; // 4
}
}

[Preety Narashimhan]

sorry for the late reply ..was outa station..
hey tx a million all ya folks
so let me get things right..
1.Protected and Static classes need to be ineer classes.Cant they stand on their own?
2.Static methods can be overidden as in
public static void print() { System.out.println("Not Final, Static"); }
could be overidden as follows?
public static void print(String str) { System.out.println("Not Final, Static Overidden? :" + str); }
3.Basically there was a question which of teh following classes can be subclassed, and one of the options was a private class so i was wondering if they can be sub-classes at all?
4.Lance, the Void that u mention is it a Wrapper class?? Since it threw compilation errors when i tried to instantiate a void type variable or pass a void argument.
5.Eureka, the code u provided, has tehm as local objects, but it still on compilation of the SubClassB throws me this compilation error :
SubClassB.java:16: Invalid expression statement.
objRefA.superClassVarA; // 4
^
1 error

[Anthony Villanueva]

1. No
2. No. See the sample code below:

public class Test52
{
public static void main (String[] args)
{
Super s = new Sub();
s.staticWhoAmI(); // no polymorphic behavior
s.whoAmI(); // polymorphic behavior
}
}
class Super
{
static void staticWhoAmI()
{
System.out.println("Super");
}
void whoAmI()
{
System.out.println("Super");
}
}
class Sub extends Super
{
static void staticWhoAmI()
{
System.out.println("Sub");
}
void whoAmI()
{
System.out.println("Sub");
}
}

3. Yes. An inner private class can be subclassed. See the sample code below:

public class Test53
{
public static void main (String[] args)
{
new Test53().amethod();
}
public void amethod()
{
Inner inner1 = new SubInner();
inner1.whoAmI();
Inner inner2 = new Inner();
inner2.whoAmI();
}
private class Inner
{
void whoAmI()
{
System.out.println("Inner");
}
}
public class SubInner extends Inner
{
void whoAmI()
{
System.out.println("SubInner");
}
}
}

4. The Void class is considered a wrapper class. It is not the same as void, of course.

[Aniket S. Kulkarni]

@Preety Narashimhan

Point no: 2
static methods can not be overidden instead they can be redefined in sub class.