CODEWITHSUNDEEP
javareflection
Abhijit Chakra
Abhijit Chakra

Reputation: 3234

Java reflection can't access dynamically changed private field values

Here I am facing some difficulties while running the java reflection code i can't access dynamically changed field values in run time using reflection in java here i am putting my code complete code snippets with outputs and expected outputs

Here is my Reflection Class

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;


public class Test1 {

    public void reflect() throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {

        TestJava instance = new TestJava();

        Class<?> secretClass = instance.getClass();





        // Print all the field names & values

        Field fields[] = secretClass.getDeclaredFields();

        System.out.println("Access all the fields");

        for (Field field : fields) {

           System.out.println("Field Name: " + field.getName());
           if(field.getName().equals("i")) {
               field.setAccessible(true);

               System.out.println("For testing" +" "+field.get(instance) + "\n");
           }

           field.setAccessible(true);

           System.out.println(field.get(instance) + "\n");

        }

     }

    public static void main(String[] args) {

        Test1 newHacker = new Test1();
        TestJava secret = new TestJava();



        try {
           secret.increment();
          newHacker.reflect();
          secret.increment(); 
          newHacker.reflect();
          secret.increment();
          newHacker.reflect();
          secret.increment(); 
          newHacker.reflect();


        } catch (Exception e) {

          e.printStackTrace();

        }

      }


}

Here i am accessing the private variables from this class

public class TestJava {

   private  int i;

   public void increment() {
       i++;

       System.out.println("Testing i value" +" "+ i);
   }

}

The Out put of this program is 

Testing i value 1
Access all the fields
Field Name: i
For testing 0

0

Testing i value 2
Access all the fields
Field Name: i
For testing 0

0

Testing i value 3
Access all the fields
Field Name: i
For testing 0

0

Testing i value 4
Access all the fields
Field Name: i
For testing 0

0

But the expected result is

Testing i value 1
Access all the fields
Field Name: i
For testing 1

1

Testing i value 2
Access all the fields
Field Name: i
For testing 2

2

Testing i value 3
Access all the fields
Field Name: i
For testing 3

3

Testing i value 4
Access all the fields
Field Name: i
For testing 4

4

Upvotes: 2

Views: 405

Answers (1)

C. K. Young
C. K. Young

Reputation: 223023

Your Test1.reflect uses a different instance of TestJava from the secret in main. (Notice there are two places where new TestJava() is called.) So calling secret.increment() won't affect the instance of TestJava used by Test1.reflect.

But if you did this:

public class Test1 {
    public void reflect(TestJava instance) throws IllegalAccessException, InvocationTargetException {
        // Everything in your original method minus the first line
    }
    // ...
}

and then used the following in main:

secret.increment();
newHacker.reflect(secret);

then things should behave as you expect.

Upvotes: 3

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