Q:

How to initialize a variable to accept any given class

I'm designing a jax-rs application.  I need to have a common response object to every api call.  This is the model of it.  UserObject variable should be modified to accept any class that I set using get/set'ers.  Currently it can only accept Customer class only.  I need this variable to be able to accept Customer,Address,Employee ..... (any thing I pass).  How can I do it? 
public class CustomResponse {
    private Customer UserObject;
    private String Attributes;
    private String Tags;
    ....
}

A:

You can use a generic class for that:
public class CustomResponse<T> {
    private T userObject;
    private String Attributes;
    private String Tags;

    //a setter...
    public void setUserObject(T object) {this.userObject = object;}
    public T getUserObject() {return this.userObject;}
}

And specific object types can be constructed as:
CustomResponse<Customer> customerResponse = new CustomResponse<Customer>();
customerResponse.setUserObject(new Customer());
...

In a different resource method:
CustomResponse<Address> customerResponse = new CustomResponse<Address>();
customerResponse.setUserObject(new Address());
...

