How to make private member more secure ?

[Manoja]

In below example I am able to access the private member variable in subclass.Is there any way I can protect my private member variable?
Means no way it will be accessible.

--------------------------
class SuperClass
{
private int x;
}

class SubClass extends SuperClass
{
public void method() throws Exception
{
SuperClass obj = new SuperClass();
Field field = obj.getClass().getDeclaredField("x");
field.setAccessible(true);

field.setInt(obj, 10);
System.out.println("The private member x vlaue :" + field.getInt(obj));
}
}

[Jeroen Wenting]

no.

If you use reflection you can break through anything (well, almost, you won't get instances of abstract classes or interfaces I think or if you do they'll be pretty useless).

One more reason to be extremely careful when using reflection.

[Ernest Friedman-Hill]

A SecurityManager can be configured to disallow this. This is certainly not a beginner question, though; I'll move it to Java in General (Intermediate) for further discussion.

[Nicholas Cheung]

A SecurityManager can be configured to disallow this.

Are there any examples for this? Could I configure how the object be created, which variables to initialize and which does not, and how the object be destroyed?

Nick

[Petr Blahos]

Make it final. You will be able to set is accessible but
not to change the value.
P.

[Cay Horstmann]

Generally, you configure a security manager with a policy file.

The simplest way to do that is to start your Java app with the command line

java -Djava.security.manager -Djava.security.policy=MyApp.policy  MyApp

Then place policy directives into the file

MyApp.policy

.

Once you have a security manager in place, reflection no longer lets you
peek into private fields. To turn the feature back on, you add a directive
such as

grant 
{
   permission java.lang.reflect.ReflectPermission suppressAccessChecks
}

to the policy file.

As you can see, you don't get any fine-grained control. Either all reflection into non-public members is allowed, or it is all forbidden.

Cheers,

Cay