Did you read the readmes, tutorials and the SampleConsoleServer example? Also please read the OPC UA Specification on how the address space works (Part 3).

From the SampleConsoleServer:
– How to expose a java variable (attribute, typed opc ua variable): See MyNodeManager and code related handling myLevel field.
– How to expose a java method: See MyNodeManager and code related to myMethod field and MyMethodManagerListener class.
– How to handle user-access (access levels, sessions): See MyUserValidator, MyIoManagerListener and read the comments in the code.

In general it is not possible to “expose” e.g. a simple java double, in case you are thinking something along e.g. JAXB, JPA, Jackson annotations. The reason that in UA there is currently 22 possible Attributes for a node. Depending on the NodeClass Attribute, some of these are mandatory, optional and not applicable. And there are 8 different NodeClasses. In addition there are References to other nodes. In short there is lots of information modelling data in addition to the Value Attribute.
However see MyBigNodeManager sample, it might be what you want or at least close (but I would recommend using NodeSet XML -> codegen -> NodeManagerUaNode.createInstance workflow if possible). Otherwise I would need a more in depth explanation what you mean by “expose”.

Ua Methods (NodeClass Method) nodes have Input/OutputArguments subnodes which defines the parameters, which have Value Attribute of Argument Structure DataType, which defines name, description, data type, possible dimensions and their sizes of the input parameters. Currently the options are codegen and MyMethodManagerListener style. If we find a better way then it could be done for next major version.