DontDoThis.java

final public class DontDoThis {

    static class SuperClass {

        SuperClass() {
            overridableMethod();  // this is a bad idea.  wait, you'll see.
        }

        protected void overridableMethod() {
        }
    }
    
    static class SubClass extends SuperClass {

        final private Integer myVeryOwnField = 1;

        @Override
        protected void overridableMethod() {
            myVeryOwnField.intValue();   // this is where you will get a NullPointerException
        }
    }


    public static void main(String[] args) {
        new SubClass();
    }
}