Stupid Compiler Optimization

FunClassTest.java

package serpentes.testing;

import org.testng.annotations.Test;

import java.lang.reflect.Field;

import static org.testng.Assert.assertEquals;

public class FunClassTest {

    @Test
    public void explainThis() {
        FunClass fun = new FunClass("value");
        assertEquals("value", fun.changeable());
        assertEquals("", fun.unchangeable());

        fun.changeable("newC");
        fun.unchangeable("newU");
        assertEquals("newC", fun.changeable());
        assertEquals("newU", fun.reflectGet("unchangeable"));

        //??WHY THE FOLLOWING
        assertEquals("", fun.unchangeable());
    }

    private static class FunClass {
        private final String changeable;
        private final String unchangeable = "";

        public FunClass(String str) {
            this.changeable = str;
        }

        public String changeable() {
            return changeable;
        }

        public String unchangeable() {
            return unchangeable;
        }

        public void changeable(String newVal) {
            reflectSet("changeable", newVal);
        }

        public void unchangeable(String newVal) {
            reflectSet("unchangeable", newVal);
        }

        @SuppressWarnings("unchecked")
        public <T> T reflectGet(String name) {
            try {
                Field field = getClass().getDeclaredField(name);
                field.setAccessible(true);
                return (T) field.get(this);
            } catch (Exception e) {
                throw new IllegalStateException("unable to set field value", e);
            }
        }

        private void reflectSet(String name, Object value) {
            try {
                Field field = getClass().getDeclaredField(name);
                field.setAccessible(true);
                field.set(this, value);
            } catch (Exception e) {
                throw new IllegalStateException("unable to set field value", e);
            }
        }
    }
}