HelloImpl.java

package examples.hello;

import java.rmi.Naming;
import java.rmi.RemoteException;
import java.rmi.RMISecurityManager;
import java.rmi.server.UnicastRemoteObject;

/** This class serves both as the remote object implementation and the
    object server main. These two functions could be separated. */
public class HelloImpl extends UnicastRemoteObject
  implements Hello {
  
  public HelloImpl() throws RemoteException {
    super();
  }
  
  public String sayHello() {
    return  "Hello World!";
  }
  
  public static void main(String args[]) { 
    
    // Create and install a security manager 
    if (System.getSecurityManager() == null) { 
      System.setSecurityManager(new RMISecurityManager()); 
    } 
    try { 
      HelloImpl obj = new HelloImpl(); 
      // Bind this object instance to the name "HelloServer" 
      Naming.rebind("HelloServer", obj); 
      System.out.println("HelloServer bound in registry"); 
    } catch (Exception e) { 
      System.out.println("HelloImpl err: " + e.getMessage()); 
      e.printStackTrace(); 
    } 
  } 
}

• The implementation must implement all methods in the interface otherwise it will be abstract.
• It extends UnicastRemoteObject so it uses RMI's default socket-based transport and runs all the time.
  • We could have made it run only when activated (more later).
• Constructor is the same as for a non-remote class.
• Arguments and return values can be anything.
• But, if argument or return value is an object then this object must implement java.io.Serializable
• Remote objects are passed just like local objects, by reference, but it's actually a reference to a stub).
• You can implement other methods but these can only be called from within the JVM running the service.