What makes Strings unique among Java Object types?

What makes Strings unique among Java Object types?

We've learned that many types in Java fall neatly into one of two categories:

• Object types (FilledRect, Text, Choice)
  • Described by a class definition
  • Created using constructor and "new" command
  • Manipulated through invocation of methods.
• Non-object (primitive) types (int, boolean, double)
  • Members of each of these types are described by constants such as 3, true, 49.7
  • Manipulated through operator symbols like +, &&, *

Java considers String to be an object type. But Strings share features with both object and non-object types.

• Can be created using a constructor and "new" command.
• Can be described by constants ("hello")
• Can be manipulated using an operator symbol (+)
• Can be manipulated by invoking methods. In fact, there are over 50 methods in the String class!

What makes Strings unique among Java Object types?