Quick Answer

Handle reflection access violations.

Understanding the Issue

This exception occurs when trying to reflectively access inaccessible class members (private/protected/package-private).

The Problem

This code demonstrates the issue:

Java Error 
Field field = MyClass.class.getDeclaredField("privateField");
Object value = field.get(instance); // Throws

The Solution

Here's the corrected code:

Java Fixed 
// Solution 1: Set accessible flag
field.setAccessible(true);
Object value = field.get(instance);

// Solution 2: Use proper public API
// Instead of accessing private fields directly

// Solution 3: Check modifiers
if (Modifier.isPublic(field.getModifiers())) {
    field.get(instance);
}

// Solution 4: Use MethodHandles (Java 7+)
Lookup lookup = MethodHandles.lookup();
MethodHandle mh = lookup.findGetter(MyClass.class, "field", String.class);
String value = (String) mh.invoke(instance);

Key Takeaways

Respect encapsulation and use reflection judiciously.