I can't say much details, but as some have already mentioned: Java can't overload operators and Java is purely object-oriented.
That means there are no free functions - everything is inside objects.
Numbers and strings and all that are not objects in C++ - they are data types, so you can't expect "something".length() to work, as it might in Java.

Java does not support generic programming and templates to my knowledge. And I'm sure there's more.
Oh, and Java can't do multiple inheritance, can it (C++ can)?