What is the use of Generic class in java

Question

hi everyone,
i want to know that
what is the use of Generic class in java ?
regards,
dhruvang

Answer 1

Simplistically...
A method is a block of code that makes some Objects in the block of code abstract (those abstract Objects are the parameters of the method). This allows us to reuse the method passing in different Objects (arguments) each time.
In a similar way, Generics allows us to take a Class and make some of the types in the class abstract. (These types are the type parameters of the class). This allows us to reuse the class, passing in different types each time we use it.
We write type parameters (when we declare) and type arguments (when we use) inside < >.
For example the List class has a Type Parameter which makes the type of the things in the list become abstract.
A List<String> is a list of Strings, it has a method "void add(String)" and a method "String get(int)".
A List<File> is a list of Files, it has a method "void add(File)" and a method "File get(int)".
List is just one class (interface actually but don't worry about that), but we can specify different type arguments which means the methods use this abstract type rather than a fixed concrete type in their declarations.
Why?
You spend a little more effort describing your types (List<String> instead of just List), and as a benefit, you, and anyone else who reads your code, and the compiler (which also reads your code) know more accurately the types of things. Because more detail is known, the compiler is able to tell you when you screw up (as opposed to finding out at runtime). And people understand your code better.
Once you get used to them, its a bit like the difference between black and white TV, and colour TV. When you see code that doesn't specify the type parameters, you just get the feeling that you are missing out on something. When I see an API with List as a return type or argument type, I think "List of what?". When I see List<String>, I know much more about that parameter or return type.
Bruce