What Exactly is a Client of a Class

Question

I always thought a client of a class is one that uses a reference to access instance fields/methods of that class i.e. another class (from its own methods). But when I think about some details there are some things that I couldn't figure out.

In Java I know of a few places where you can place action statements.

• Inside a method (instance/static)
• Inline initialization (when you declare an instance variable like in private int x = 5;)
• Static block

Maybe there are more that I don't know or remember.

The first part of the question is are all of these considered clients if they are in another class? Also can they access private stuff when they are in the same class?

The second part is: When JVM calls a method (like main and finalize) are they considered clients, too? (the calls are not from a class?)

Edit: Can a client access only public methods and variables? Can't we call it a client if it accesses package fields (if in the same package).

Answer 1

Before diving into Java -lets try to map the situation to a physical world scenario.

You go to a pastry shop and order a pastry. You get the pastry from the store pay for it and leave. You naturally call yourself a client of the store. So what did we understand from this?

The term client refers to any entity that requests a service from another entity. The client does not bother about how the entity providing the service actually provides the service - the client is happy as long as the service is available and fulfills its use case.

Hence, when a method M1 within a class calls another method M2 then M1 is a client of M2. Similarly when a class C1 requests service of C2 then C1 is a client of C2.

Coming to your question about main(), finalize() and the interaction with JVM - You can consider the class-loader of the JVM as the client of your class since it loads JVM class loader will load your class and then request the main method to begin execution and continue further processing. EDIT based on comment from the OP - finalize() method is accessed by the Garbage Collector within the JVM using some internal JVM tricks. As a general rule within any normal application will not perform such trickery.