Client.findById（id）是什么意思？

Question

Looking through the Play documentation for Java I noticed the following block of code:

public static Result show(Long id) {
  Client client = Client.findById(id);
  return ok(views.html.Client.show(client));
}

Source: http://www.playframework.com/documentation/2.1.0/JavaRouting

I am having some trouble understanding the second line, my understanding of Java Object creation is a typical constructor looks like the following:

Person john = new Person();

What is the second line doing? Creating a Object called client from Class called Client, also what is Client? It doesn't appear to be a part of the Play Framework, certainly I cannot find anything in JavaDocs.

Thanks

Edit:

I found this to be a good point of reference for the answer ( http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html )

Also I think the class Client comes from the following documentation ( http://www.playframework.com/documentation/1.1.1/controllers ) with Client being just a example model class, the new documentation probably needs updating to clear up this confusion.

Answer 1

There must be a static method called show(Client) on the views.html.Client class that returns some object. That object is passed into an ok(whatever) method, and that ok method returns a Result object.

Answer 2

Pretty clearly, the class Client has a static function of findById , which takes a Long and returns a Client . Static functions are functions that are defined without any access to object properties, and therefore can be accessed through the class name, rather than having to be accessed through an object. Most likely, the class has a static property containing a collection of all clients in the system by index, and findById grabs an existing Client from that list.

I really have no idea where the class Client is defined, however. I've also made a quick look around for it, and couldn't find it in the obvious places.

Answer 3

You're missing some basic knowledge/experience. The sample you gave has nothing to do with routes and in this snippet only first line is important, second is just some hypothetical usage. De facto it could be just...

public static Result show(Long id) {
  return ok("You want to display details of client with ID: " + id);
} 

Although @BenBarden explained what is that mean correctly , this static method isn't declared anywhere, it's (again) hyphotetical usage of some ORM. For an example the real usage with Ebean's model will be:

Client = Client.find.byId(id);

Of course you can also declare own method in your Client model and name it the same as in the sample, however it will be just only wrapper:

public static Finder<Long, Client> find
        = new Finder<>(Long.class, Client.class);

public Client findById(Long id) {
    return find.byId(id);
}

Conclusions

• You need to examine some samples available with your Play sources to get familiar with some basic syntax, fortunately you'll find it easy.
• DO NOT MIX documentation from Play 1.x with Play 2.x they are not compatible!