What is Distributed Application? Explain the steps to create RMI applications using example.

 A Distributed Application is a software system that runs on multiple computers, connected through a network, and works together to perform a task. These applications are designed to leverage the benefits of distributed computing, such as scalability, fault tolerance, and high performance.

RMI (Remote Method Invocation) is a Java API that allows a Java object running in one JVM (Java Virtual Machine) to invoke methods on an object running in another JVM, thus enabling distributed computing. Here are the steps to create RMI applications:

1. Define the remote interface:

The remote interface defines the methods that can be invoked remotely by the client. This interface must extend the java.rmi.Remote interface and declare all the methods that can be invoked remotely.

For example:

public interface Calculator extends Remote {
    public int add(int x, int y) throws RemoteException;
    public int subtract(int x, int y) throws RemoteException;
    public int multiply(int x, int y) throws RemoteException;
    public int divide(int x, int y) throws RemoteException;
}

2. Implement the remote interface:

The implementation of the remote interface contains the actual implementation of the methods defined in the interface. This implementation must extend the java.rmi.server.UnicastRemoteObject class and implement the remote interface.

For example:

public class CalculatorImpl extends UnicastRemoteObject implements Calculator {
    public CalculatorImpl() throws RemoteException {
        super();
    }
    public int add(int x, int y) throws RemoteException {
        return x + y;
    }
    public int subtract(int x, int y) throws RemoteException {
        return x - y;
    }
    public int multiply(int x, int y) throws RemoteException {
        return x * y;
    }
    public int divide(int x, int y) throws RemoteException {
        return x / y;
    }
}

3. Create the server program:

The server program creates an instance of the remote object, binds it to a name in the RMI registry, and waits for incoming client requests.

For example:

public class CalculatorServer {
    public static void main(String[] args) {
        try {
            Calculator calculator = new CalculatorImpl();
            Naming.rebind("CalculatorService", calculator);
            System.out.println("CalculatorService bound in registry");
        } catch (Exception e) {
            System.err.println("Calculator exception: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

4. Create the client program:

The client program looks up the remote object in the RMI registry, obtains a reference to the remote object, and invokes its methods.

For example:

public class CalculatorClient {
    public static void main(String[] args) {
        try {
            Calculator calculator = (Calculator) Naming.lookup("rmi://localhost/CalculatorService");
            int sum = calculator.add(5, 10);
            int difference = calculator.subtract(5, 10);
            int product = calculator.multiply(5, 10);
            int quotient = calculator.divide(5, 10);
            System.out.println("5 + 10 = " + sum);
            System.out.println("5 - 10 = " + difference);
            System.out.println("5 * 10 = " + product);
            System.out.println("5 / 10 = " + quotient);
        } catch (Exception e) {
            System.err.println("Calculator exception: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

In this example, the server program creates an instance of the CalculatorImpl class, which implements the Calculator remote interface. The server program then binds this object to a name ("CalculatorService") in the RMI registry. The client program looks up this object in the registry using the Naming.lookup() method and invokes its methods