Week 10

Question 1

What is networking in Java?

Answer 1

Java provides a framework for communication between machines using:

TCP (Transmission Control Protocol): Reliable, connection-based

UDP (User Datagram Protocol): Unreliable, connectionless

Question 2

What are sockets in networking?

Answer 2

A socket is a connection endpoint for sending and receiving data between two machines

Sockets are bound to a specific port on a server to listen for client requests

Question 3

What are the differences between TCP and UDP?

Answer 3

TCP:

Connection-based

Guarantees data delivery and order

Error-checked and reliable

Example applications: HTTP, FTP

UDP:

Connectionless

No guarantee of delivery or order

Lightweight and faster due to minimal overhead

Example applications: Streaming, DNS

Question 4

What are ports in networking?

Answer 4

A port is a 16-bit number used to direct data to specific applications on a machine

Well-known ports: 0-1023 (e.g., port 80 for HTTP)

Used in both TCP and UDP communication

Question 5

What is required for socket communication?

Answer 5

Server:

Runs on a specific machine (IP address) and listens on a port

Accepts client connections and creates a new socket for communication

Client:

Knows the server’s hostname and port

Opens a connection to the server’s socket

Question 6

How do you read/write data using sockets in Java?

Answer 6

1. Open a socket
2. Open input/output streams to the socket
3. Read and write data using the streams
4. Close the streams
5. Close the socket

Question 7

What are Java classes for TCP and UDP communication?

Answer 7

TCP:

Socket and ServerSocket: For client-server communication

URL and URLConnection: For HTTP connections

UDP:

DatagramPacket: Represents a UDP packet

DatagramSocket: For sending and receiving packets

MulticastSocket: For group communication

Question 8

How is data sent and received with UDP?

Answer 8

Data is sent as independent packets (datagrams)

No dedicated channel is established

The receiver must handle missing or out-of-order packets

Question 9

What are client-server pairs in Java?

Answer 9

Server:

Creates a ServerSocket to listen for incoming connections

Accepts a client connection and communicates via a new Socket

Client:

Creates a Socket to connect to the server’s IP and port

Exchanges data with the server through streams

Question 10

What are common uses of TCP and UDP?

Answer 10

TCP:

Reliable communication for web services, file transfers

UDP:

Fast communication for streaming, gaming, or broadcasting

Question 11

What are the key advantages of using TCP over UDP?

Answer 11

Ensures data integrity and order

Better for applications where reliability is critical

Question 12

What are the advantages of UDP over TCP?

Answer 12

Lower latency

Suitable for real-time applications where minor data loss is acceptable

Question 13

What is Java RMI?

Answer 13

A framework allowing objects in one JVM to invoke methods on objects in another JVM

Facilitates remote communication between Java programs on different machines

Question 14

What are the basic components of RMI?

Answer 14

Registry: Maps names to remote objects using bind and rebind

Server: Registers remote objects with the RMI registry and waits for client invocations

Client: Looks up remote objects in the registry and invokes methods on them

Question 15

What is required for an object to be remote?

Answer 15

The object must implement an interface extending java.rmi.Remote

Methods in the interface must declare throws java.rmi.RemoteException

Question 16

What are the steps to create an RMI service?

Answer 16

1. Define a remote interface
2. Implement the interface in a concrete class (remote implementation)
3. Use the Java compiler to generate stubs and skeletons
4. Start the RMI registry
5. Start the remote service

Question 17

What is the role of the RMI registry?

Answer 17

A server-side process that allows clients to look up and obtain references to remote objects by name

Question 18

What are stubs and skeletons in RMI?

Answer 18

Stub: Client-side helper that communicates with the server’s remote object

Skeleton: Server-side helper that dispatches client requests to the appropriate method on the remote object (deprecated in modern Java)

Question 19

How is security managed in RMI?

Answer 19

Permissions are set using security policies defined in .policy files

Security settings control access to local and remote resources

Question 20

What is the java.rmi.RemoteException?

Answer 20

A checked exception that must be declared by methods in remote interfaces

Indicates errors during remote communication

Question 21

What is the Compute Engine example?

Answer 21

Demonstrates a server executing arbitrary tasks sent by clients

The server does not need to know the task definitions beforehand

Question 22

What are the key RMI runtime settings?

Answer 22

-Djava.rmi.server.codebase: Specifies the location of the remote class definitions

-Djava.security.policy: Specifies the security policy file

Question 23

What are some common RMI methods?

Answer 23

Server-side:

bind(String name, Remote obj)

rebind(String name, Remote obj)

Client-side:

lookup(String name)

Question 24

What are the limitations of RMI?

Answer 24

Limited to Java applications

Performance overhead due to serialization and deserialization

Requires careful handling of security and network configurations