ChangingStaticFinalsIsStupid.java

package test;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

public class ChangingStaticFinalsIsStupid {
    static class Value {
        // It's Integer, so not a compile time constant
        public static final Integer VALUE = 10;
    }
    
    static void setFinalField(Field field, Object newValue) throws Exception {
        field.setAccessible(true);
        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
        field.set(null, newValue);
    }
    
    static Integer useField() {
        for (int i = 0; i < 1_000_000; i++) {
            if (Value.VALUE != 10) {
                return Value.VALUE;
            }
        }
        return Value.VALUE;
    }
    
    public static void main(String args[]) throws Exception {
        // Comment out the next line for a different result
        useField();
        useField();
        setFinalField(Value.class.getField("VALUE"), 200);
        System.out.println(useField());
    }
}