Java reflection example to change final member

ReflectionChangeFinalMember.java

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

// Extended code from https://stackoverflow.com/questions/3301635/change-private-static-final-field-using-java-reflection
// to support change of final members of an instance.
public class ReflectionChangeFinalMember {

  static void setFinalMemberOfObject(Object target, Field field, Object newValue) throws Exception {
    field.setAccessible(true);

    Field modifiersField = Field.class.getDeclaredField("modifiers");
    modifiersField.setAccessible(true);
    modifiersField.set(field, field.getModifiers() & ~Modifier.FINAL);

    field.set(target, newValue);
  }

  public static void main(String args[]) throws Exception {
    Map<Integer, String> changedMap = new HashMap<Integer, String>() {
      {
        put(1, "UNO");
      }
    };

    A a = new A();
    System.out.printf("A.getSteOne = %s%n", a.getStepOne()); // original map

    Field stepsField = a.getClass().getDeclaredField("steps");
    setFinalMemberOfObject(a, stepsField, changedMap);
    System.out.printf("A.getSteOne = %s%n", a.getStepOne()); // changed map
  }

}

class A {

  private final Map<Integer, String> steps = Collections.unmodifiableMap(new HashMap<Integer, String>() {
    {
      put(1, "one");
    }
  });

  public String getStepOne() {
    return steps.get(1);
  }
}