Generic

Generic collections were introduced in Java 1.5 and since then have become preferable to non-generic collections. A non-generic collection defaults to being a collection of Objects, and in order to effectively use those Objects, you need to cast them as their correct data type during use. A generic collection knows what type of object it contains, and thus no casting is needed.

It's just like 'Java Class, and 'Class Room'. In a 'Java Class', the faculty have to teach only java related topics. And the students in the class must belongs to 'Java' subject. Means it is specific for 'Java' only.i.e., A Platform is a specific one where all the functionality are predefined. Where as, a 'Class Room' is a Generic one where java/.net/php/flex, N-number of classes can be conducted. Like wise, an Environment is a generic one where the needs for platform is provided.

Generics are a part of generic programming within Java. They are commonly used to hold objects of any type, within a Java Collection Framework (JCF), and are a reusable data collection tool.

Only Objects can be used as generic arguments. Primitives Data Types (int, long, char ...) are not objects. But you can use Integer, an Object that wrap the data type int instead.