Can a package final variable be changed through reflection?

问题

Say I have this:

public class Widget {
  final int val = 23;
}

Can the val be changed through reflection if made accessible?

If so, is there any way to prevent it that without using the security manager?

回答1:

Turns out, changing final members causes reflection-obtained values to differ from values returned by regular code! This is quite scary.

import java.lang.reflect.Field;

public class Test {

    private static final class Widget {
        private final int val = 23;

        public int getVal() {
            return val;
        }
    }

    public static void main(String[] args) throws Exception {
        Widget w = new Widget ();

        Field m = Widget.class.getDeclaredField("val");

        m.setAccessible(true);

        m.set(w, 233);

        Field m1 = Widget.class.getDeclaredField("val");
        m1.setAccessible(true);


        System.out.println(m.get(w)); /// PRINT 233
        System.out.println(w.getVal()); /// PRINT 23
        System.out.println(m1.get(w)); /// PRINT 233

    }
}

回答2:

YES. Try this code:

public static void main(String[] args) throws Exception {
    Widget w = new Widget ();

    Field m = Widget.class.getDeclaredField("val");

    m.setAccessible(true);

    m.set(w, 233);

    System.out.println(m.get(w)); /// PRINT 233
}

回答3:

Try this.

 Widget() {
     checkPerMission();
  }
     private void checkPerMission() {
         Class self = sun.reflect.Reflection.getCallerClass(1);
          Class caller = sun.reflect.Reflection.getCallerClass(3);
         if (self != caller) {
             throw new java.lang.IllegalAccessError();
         }

 }

来源：https://stackoverflow.com/questions/23894354/can-a-package-final-variable-be-changed-through-reflection

标签

java

access-modifiers