Generics - This long-awaited enhancement to the type system allows a type or method to operate on objects of various types while providing compile-time type safety. It adds compile-time type safety to the Collections Framework and eliminates the drudgery of casting. See the Generics lesson in the Java Tutorials. (JSR 14)
Enhanced for Loop - This new language construct eliminates the drudgery and error-proneness of iterators and index variables when iterating over collections and arrays. (JSR 201)
Autoboxing/Unboxing - This facility eliminates the drudgery of manual conversion between primitive types (such as int) and wrapper types (such as Integer). (JSR 201)
Typesafe Enums - This flexible object-oriented enumerated type facility allows you to create enumerated types with arbitrary methods and fields. It provides all the benefits of the Typesafe Enum pattern (Effective Java, Item 21) without the verbosity and the error-proneness. (JSR 201)
Varargs - This facility eliminates the need for manually boxing up argument lists into an array when invoking methods that accept variable-length argument lists.
Static Import - This facility lets you avoid qualifying static members with class names without the shortcomings of the "Constant Interface antipattern." (JSR 201)
Annotations (Metadata) - This language feature lets you avoid writing boilerplate code under many circumstances by enabling tools to generate it from annotations in the source code. This leads to a "declarative" programming style where the programmer says what should be done and tools emit the code to do it. Also it eliminates the need for maintaining "side files" that must be kept up to date with changes in source files. Instead the information can be maintained in the source file. (JSR 175) NOTE: The @Deprecated annotation provides a way to deprecate program elements. See How and When To Deprecate APIs.
