Access Control in Java Reflection

Introduction

By Default:
- We cannot access private fields, methods, or constructors of another class directly.
- Even if we try to access private members using Reflection without any special permission, it will throw an IllegalAccessException.
But we can bypass Java's access control checks and access private members of any class.
For this, Java Reflection provides the setAccessible(true) method which can be called on Field, Method and Constructor objects.
So, Access Control in Reflection API decides whether our code can access fields, methods or constructors of a class, especially private ones.

Program:

Program 1: Accessing a private field with and without setAccessible(true)

import java.lang.reflect.*;

class Demo
{
    private String secret = "This is private";

    private void showSecret()
    {
        System.out.println("Secret: " + secret);
    }
}

public class MainApp
{
    public static void main(String[] args) throws Exception
    {
        Demo obj = new Demo();
        Class<?> c = obj.getClass();

        // Try to access private field without setAccessible()
        Field f = c.getDeclaredField("secret");

        try
        {
            System.out.println(f.get(obj)); // ❌ Throws IllegalAccessException
        }
        catch (IllegalAccessException e)
        {
            System.out.println("Cannot access private field without setAccessible(true)");
        }

        // Now bypass access control
        f.setAccessible(true); // ✅ Disables access checks
        System.out.println("Private Field Value: " + f.get(obj)); // Works fine
    }
}

Output:

Cannot access private field without setAccessible(true)
Private Field Value: This is private

Program 2: Accessing both a private field and a private method using setAccessible(true)

import java.lang.reflect.*;

class Student
{
    private String name = "Deepak";

    private void showMessage()
    {
        System.out.println("Hello from private method!");
    }
}

public class MainApp
{
    public static void main(String[] args) throws Exception
    {
        Student s = new Student();
        Class<?> c = Student.class;

        // Access private field
        Field field = c.getDeclaredField("name");
        field.setAccessible(true); // ✅ bypass access control
        System.out.println("Private Field Value: " + field.get(s));

        // Access private method
        Method method = c.getDeclaredMethod("showMessage");
        method.setAccessible(true); // ✅ allow invocation
        method.invoke(s);
    }
}

Output:

Private Field Value: Deepak
Hello from private method!

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Access Control in Java Reflection

Introduction

Program:

Output:

Output:

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