Autoboxing is not foolproof

gistfile1.java

// Duck.java
class Duck {
    public static void quack(Integer num) {
        System.out.println(num);
    }
}

// Main.java
class Main {
    public static void main(String[] args) {
        Duck.quack(42);
    }
}

/*

How to make this program crash
==============================

Compile both classes:

  $ javac Duck.java
  $ javac Main.java

Execute main:

  $ java Main

It should say 42. Autoboxing works.

-----

Now change the line

  .. quack(Integer num) {

to

  .. quack(int num) {

Re-compile Duck, but *don't* re-compile Main:

  $ javac Duck.java

Now try running Main:

  $ java Main

  Exception in thread "main" java.lang.NoSuchMethodError: Duck.quack(Ljava/lang/Integer;)V
	  at Main.main(Main.java:5)

Crash!

*/