Final variable manipulation in Java

Question

Could anyone please tell me what is the meaning of the following line in context of Java:

final variable can still be manipulated unless it\'s immut

Answer 1

The following is code I created several years back to turn final off and then back on so you can modify the reference/value, it will only work on variables, but it does work.

You can also do something similar with method handles, however unless you are writing some form of auto object parser/generator, I would avoid doing either like the plague.

public static void setValueOnField(Object instance, Field field, Object value)
        throws NoSuchFieldException, IOException, IllegalArgumentException,
        IllegalAccessException {
    try (Accessor access = open(field)) {
        field.set(instance, value);
    }
}


  public static class Accessor
            implements Closeable {
        private final boolean isAccessible;
        private final boolean isFinal;
        private final int modifiers;
        private final T accessibleObject;

        private Accessor(T accessibleObject) throws IOException {
            super();
            if (accessibleObject == null) {
                throw new IOException(
                        "Error preparing field for accesibility: Field is null");
            }
            try {
                this.accessibleObject = accessibleObject;
                this.modifiers = accessibleObject.getModifiers();
                this.isAccessible = accessibleObject.isAccessible();
                this.isFinal = Modifier.isFinal(modifiers);
                if (!this.isAccessible) {
                    accessibleObject.setAccessible(true);
                }
                if (this.isFinal) {
                    getModifiersField(accessibleObject).setInt(
                            accessibleObject, modifiers & ~Modifier.FINAL);
                }
            } catch (Exception e) {
                throw new IOException("Error preparing field for accesibility",
                        e);
            }

        }

        @Override
        public void close() throws IOException {

            if (!this.isAccessible) {
                accessibleObject.setAccessible(false);
            }
            if (this.isFinal) {
                try {
                    getModifiersField(accessibleObject).setInt(
                            accessibleObject, modifiers);
                } catch (Exception e) {
                    throw new IOException("Error setting field to final", e);
                }
            }
        }

        public T getAccessibleObject() {
            return accessibleObject;
        }

        private static Field getModifiersField(AccessibleObject toFetch) {
            Field field;
            try {
                field = toFetch.getClass().getField("modifiers");
                field.setAccessible(true);
                return field;
            } catch (Exception e) {
                throw new RuntimeException(
                        "Error occured getting modifiers field", e);
            }
        }
    }