Autoboxing making people lazy

When writing in Java5 primitive types get automatically converted to objects if they are needed. This means that you can write code like:

  map.put(1,4);

where before you needed

  map.put(Long.valueOf(1), Long.valueOf(4));

This is nice, and makes code prettier and easier to read.

Unfortunately it makes programmers lazy, and they don't pay attention to if they are using Long or long in methods, and may pass a Long to a method that takes a long. Like this:

public void suspicious(Long l) {
  foo(l); // <-- Here
} 

private void foo(long l) {
  System.err.println("Long was: " + l);
}

One problem is that the JVM will be creating and deleting lots of boxing objects all over the place if your code is particularly inconsistent. However, there's a more subtle problem. This code can now NPE at the line marked Here, and it's can be difficult to track down.