Is it possible to invoke private attributes or methods via reflection

Question

I was trying to fetch the value of an static private attribute via reflection, but it fails with an error.

Class class = home.Student.class; Field field = studentClass.getDeclaredField("nstance"); Object obj = field.get(null); 

The exception I get is:

java.lang.IllegalAccessException: Class com.test.ReflectionTest can not access a member of class home.Student with modifiers "private static". 

Moreover, there is a private I need to invoke, with the following code.

Method method = studentClass.getMethod("addMarks"); method.invoke(studentClass.newInstance(), 1); 

but the problem is the Student class is a singleton class, and constructor in private, and cannot be accessed.

Answer 1

You can set the field accessible:

field.setAccessible(true); 

Answer 2

Yes it is. You have to set them accessible using setAccessible(true) defined in AccesibleObject that is a super class of both Field and Method

With the static field you should be able to do:

Class class = home.Student.class; Field field = studentClass.getDeclaredField("nstance"); field.setAccessible(true); // suppress Java access checking Object obj = field.get(null); // as the field is a static field                                 // the instance parameter is ignored                                // and may be null.  field.setAccesible(false); // continue to use Java access checking 

And with the private method

Method method = studentClass.getMethod("addMarks"); method.setAccessible(true); // exactly the same as with the field method.invoke(studentClass.newInstance(), 1); 

And with a private constructor:

Constructor constructor = studentClass.getDeclaredConstructor(param, types); constructor.setAccessible(true); constructor.newInstance(param, values);