cop3252 lamba expressions & networking

lambda calculus

the basis of functional programming languages

strategy pattern

passing a method into another method

lambda expressions

used with functional interfaces, replaces many uses of anonymous inner classes, and represents an anonymous method or function

lambda syntax

(parameters) → {statements}

void PrintHello() {

System.out.println(“Hello, World”); }

() → System.out.println(“Hello, World”)

double average (double x, double y, double z) { return(x+y+z)/3.0; }

(double x, double y, double z) → (x+y+z)/3.0

void UpdateIfOdd (int x) {

if (x%2≠0) {

y=10;

System.out.print(“y is now “ +y); }

x → { if (x%2≠0) y=10; System.out.print(“y is now “ +y); }

cilent

requests some information or action

server

performs action and responds to the cilent

connection-based service

a cilent and server form a connection and communicate back and forth until the connection is given up

connectionless service

a cilent and server communicate by sending individual packets back and forth

socket

a software construct that represents 1 endpoint of a connection

contains Java’s fundamental networking capabilities

package.java.net

URL stands for

uniform resource locator

class for wrapping up a URL and working with it (contains many get methods)

java.net.URL

stream sockets

TCP communication, used for connection-oriented communcation between a cilent and server 

datagram sockets

UDP communication, used for connectionless communcation between programs 

UDP

user datagram protocol, most common protocol for connectionless communication

TCP

transmission control protocol, most common protocol for connection-based transmission

SSH is

connection-oriented

port number

identifies the application on the host computer

queue length

max number of cilents that can connect to server

Server: create a ServerSocket object

ServerSocket serv=new ServerSocket (portNumber, queueLength);

Server: listen for a cilent connection

Socket connection=serv.accept();

Server: close the socket

connection.close();

Server: input and output streams

OutputStream os = connection.getOutputStream();

InputStream is = connection.getInputStream();

Cilent: create a socket to connect to the server

Socket connection = new Socket (serverAddress, port);

class DatagramSocket

used for creation of datagram sockets

creation of datagram sockets

DatagramSocket s1, s2;

s1 = new DatagramSocket(12345); // bind to port 12345

s2 = new DatagramSocket(); // bind to any available port on local host machine

class DatagramPacket

used to build packets of information to send over datagram sockets

create a packet for storing up to 500 bytes of data that will be used to receive a datagram packet

DatagramPacket p1, p2;

byte[] data1=new byte[500]; 

p1=new DatagramPacket(data1, data1.length);

send a packet

s2.send(p2);

receive a datagram packet

s1.receive(p1);

convert a string to a byte array and create a datagram packet of outgoing data (“Hello, World”), set the port number to 1234

String message=”Hello, World”;

byte[] data2=message.getBytes();

p2 = new DatagramPacket (data2, data2.length, InetAddress.getLocalHost(), 1234);