How to Access package private Class from a Class in some other package?

Question

I have following classses

Hello.java

package speak.hello;

import java.util.Map;

import speak.hi.CustomMap;
import speak.hi.Hi;

public cla         


        

Answer 1

I don't recommend to use non-API classes as they might change in any future version and can break your code.

How did you find out about this class? Is it an Open Source library?

Try to contact the authors of the library, tell them your use case and find a way with them to offer a public API. If it's an open source library you could help them by providing a patch.

Answer 2

Is there any other way to do this ? Using reflection perhaps ?

Yes. Reflection can be used to bypass the Java access rules, if your application has full privilege.

For instance, to access a private field of an object from a different class, you need to:

• Get the object's Class object.
• Use the Class.getDeclaredField(...) method to get a Field object for the field.
• Call Field.setAccessible(true) to turn off the access check.
• Call Class.getField(object, Field) to get the field's value (or boxed value if it is a primitive type).

If the class itself is not accessible, you need to make sure that you don't refer to the classes identifier in your source code ... 'cos that will result in a compilation error. Instead, assign its reference to (say) variable of type Object or of some other visible supertype, and perform more specific operations on the instance reflectively.

---

As you might imagine, this is tedious and error prone. You'd be advised to find a better way, like:

• getting the suppliers of the classes to fix whatever is causing you to need to break the visibility restrictions,
• getting the suppliers of the classes to change their visibility,
• finding another way to use the classes that doesn't require breaking open their abstraction, or
• ditching them and finding (or writing) something better.

(Generally speaking, if you have to break open an abstraction then something is wrong with either the abstraction itself or the way you are using it.)

---

Finally, I should add that untrusted code is (should be) run in a security sandbox that blocks the use of the key reflective operations.

Answer 3

I think by default the class will be "default" (package private, you can say), NOT "private". So it can be accessed with in the same package.

Moreover, you CANNOT make any *top level class Private in Java.

And if you want make a class default and still be able to access it in other package then what will be the purpose of having access specifiers (modifiers) ??

you either need to make class public or move to the same package.

Answer 4

Following method Invokes default scoped class method using reflection

public void discardMap() {
    //CustomMap map = (CustomMap) hi.getMap();
    //map.discard();
    try {
        Object o =hi.getClass().getMethod("getMap").invoke(hi);
        Method m = o.getClass().getMethod("discard");
        m.setAccessible(true);
        m.invoke(o);
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}