I had one experience in java6 to java7 migration. The issue was a partly overriding of a list implementation. That list implementation was used in a for loop. The way the for loop was iterated across over was different in the two java versions.

e.g.

  for(Object a:list){
    a.doSomething();
  }

In java6 it was equivalent to

  for (int i:i<list.length();i++){
    list.get(i).soSomething(); 
  }

In java7 it was done like this

  Iterator iter = list.iterator();
  while(iter.hasNext() { 
    iter.next().doSomething(); 
  }

The original programmer had overridden the get method but not the next method in the iterator method. (Actually just called toLowerCase on a list of strings).

Oracle did nothing wrong, the programmer only partly overriding the list implementation was broken. This kind of programmer error is too common and is normally the reasons that upgrades become an issue, i.e. its the equivalent of using undefined behaviour in C and then scream when your compiler upgrade burns down your house.

I'm crying laughing right now. Businesses rarely see the advantages of upgrading something "Already Works". Now you could agree (and be right to a point) that it's the responsibility of developers/ops/etc to convince the business side but in my experiance the people writing the code are far enough detached from the people making decisions that they have next to no voice. My last job I saw an upgrade from Drupal 5 -> 7 and currently I work on framework that was last actively developed on 5 years ago (never versions have been released, they are now 2 major versions ahead of us which is a lifetime in PHP as of late with all it's changes). A lot of times you come into a place that is so far behind that to move up to the newest version would be equivalent to a full re-write (whereas moving up over time would have been possible had there been a bigger push for it).

2 years is not a long time to migrate large system that works fine except for minor maintenance. It isn't just time, it is finding budget for churn work.

You are talking about Sun really. But Java got really stale when Oracle bought Sun and no one cared about Java language for a few years. That's why 7 was so late and had almost no features. Everything in 8 was supposed to be in 7.