Is it possible to invoke private attributes or methods via reflection
JavaReflectionJava Problem Overview
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.
Java Solutions
Solution 1 - Java
You can set the field accessible:
field.setAccessible(true);
Solution 2 - Java
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);
Solution 3 - Java
Yes, you can "cheat" like this:
Field somePrivateField = SomeClass.class.getDeclaredField("somePrivateFieldName");
somePrivateField.setAccessible(true); // Subvert the declared "private" visibility
Object fieldValue = somePrivateField.get(someInstance);