Q without A

1. Nature's last word
2. why using single quotes update variable? not double quotes?

   $ export PS1='${RANDOM} $ '
   $ export PS1="${RANDOM} $ "

3. In svn, this is not working:

   $ svn copy -r 9 file:///Users/username/myrepos/trunk/baz.c baz.c
   // however this is working:
   $ svn copy file:///Users/username/myrepos/trunk/baz.c@9 baz.c

4. Why using %s to display enum type values?

   // getScale() returns enum type
   out.printf("%5.2f degrees %s%n", getNumber(), getScale());

5. Java, what's the difference between:

   List<String> list = new ArrayList<String>(Arrays.asList("one", "two", "", "three"));
   // version 1:
   List<String> sub = new ArrayList<String>(list.subList(1,3));
   // version 2:
   // work
   list.remove(sub);
   List<String> sub2 = list.subList(1,3);
   // won't work:
   list.removeAll(sub2); // why???

6. why does this work:

   public class Wildcards {
       public static void main(String[] args) {
           Holder<?> unbounded = new Holder<Long>();
           Long lng = 1L;
           Object r11 = wildSubtype(unbounded, lng);  // why can pass in Holder<?> to wildSubtype(Holder<? extends T> holder, T arg)?
       }
       
       static <T> T wildSubtype(Holder<? extends T> holder, T arg) {
           T t = holder.get();
           return t;
       }
   }
   
   class Holder<T> {
       private T value;
       public Holder() {}
       public Holder(T val) { value = val; }
       public void set(T val) { value = val; }
       public T get() { return value; }
   }

7. d
8. d
9. d
10. d
11. d
12. d