How to Resolve Illegal Access Exception When Accessing Parent Class Attributes via Introspection?

What causes IllegalAccessException when accessing attributes of a parent class via reflection in Java?

// Java code demonstrating reflection access
Class<?> parentClass = ParentClass.class;
Field field = parentClass.getDeclaredField("attributeName");
field.setAccessible(true); // Bypass access modifiers
Object value = field.get(parentObject);

IllegalAccessException in Java typically occurs when you attempt to access a class member (field or method) that is not accessible due to its visibility modifier (private, protected). This can arise during reflection, particularly when trying to access attributes of a parent class.

// Example demonstrating correct field access using reflection
Class<?> parentClass = ParentClass.class;
Field field = parentClass.getDeclaredField("privateField");
field.setAccessible(true); // Modify accessibility
Object value = field.get(parentObject); // Now this should work!

Causes

• Attempting to use reflection on private fields without setting accessibility correctly.
• Accessing protected or private attributes from a child class without proper permissions.
• Classpath issues and mismatched security policies.

Solutions

• Ensure you are using the appropriate access modifiers (private, protected) when trying to access fields or methods.
• Use `setAccessible(true)` on the Field object to bypass access control checks appropriately.
• Check your design to see if there are better ways to expose data rather than using reflection.

Mistake: Not calling `setAccessible(true)` before accessing a private field.

Solution: Always call `setAccessible(true)` on the Field object to bypass accessibility checks.

Mistake: Attempting to fetch class attributes before ensuring the class type is correct.

Solution: Ensure you are reflecting on the correct class and that the field exists.