Reading the release notes of gcc 4.3 at http://gcc.gnu.org/gcc-4.3/porting_to.html will give you a little bit surprise about how significant the gcc community has done.

An example.

#include <iostream.h>

int main()
{
  cout << "I'm too old" << endl;
  return 0;
}

Compiling with previous compilers gives:

warning: #warning This file includes at least one deprecated or
antiquated header. Please consider using one of the 32 headers found
in section 17.4.1.2 of the C++ standard. Examples include substituting
the <X> header for the <X.h> header for C++ includes, or
<iostream> instead of the deprecated header
<iostream.h>. To disable this warning use -Wno-deprecated.

But now says:

error: iostream.h: No such file or directory
In function 'int main()':
6: error: 'cout' was not declared in this scope
6: error: 'endl' was not declared in this scope

Hotspot code includes "*.h" version almost everywhere, so we have to change our code to meet the upcoming change of gcc.