Java
Banuprakash C
banu@lucidatechnologies.com
banuprakashc@yahoo.co.in
-----------------------------
Week 1:
Java as a Programming Language
Week 2:
Web Development using Servlet and JSP
JPA
Spring Core Container
Week 3:
Spring MVC
Spring RESTful Webservices
Spring Security
-----------------------------------------
OOP
Object Oriented Programming
Programming which resemble real world
Object communicates with other by sending a message. What messages object can
accept is exposed thro its interface.
OBject just needs to know what the message does rather than how it is going to work
----
OOP should follow SOLID Design Principles
S ==> Single Responsibility
O ==> Open Close Principle (OCP)
Open for Extension
Closed for Change
L ==> Liskov Substitution Principle
I ==> Interface seggregation
D ==> Dependecy Injection
------
What is Java?
Java is a technology
==> Platform + APIs
to execute a certain kind of code called as ByteCode
How do you generate a bytecode?
Choose a programming language and compile
Java Prog Lang ---> Java Compiler ---> ByteCode
Kotlin Prog ---> Kotlin Compiler ---> Bytecode
Groovy Prog ---> Groovy Compiler ----> Bytecode
ByteCode is portable [ Platform Independent and Architecture Neutral]
=============================================
Object --> state and behaviour
Templates for Objects
class , Type, function, ..
class Account {
}
Account sa = new Account();
function Account () {
}
var sa = new Account();
==========
Logically grouping of Objects/classes
a) Entity / Domain / Model
==> Business data
Customer, Trip, Payment, Driver, Vehicle
b) DAO ==> Data Access Object
c) Business
d) Service ( Facade)
void transferFunds(Account fromAcc, Account toAcc, double amt) {
}
e) UI
f) Utility
============
https://xxxxx-6080.cloudlab.jnaapti.io/vnc.html
Eclipse IDE
Comments:
for Developers
a)
/*
*/
b) // single line comment
for API users
Java Doc Comments
/**
*/
=======
ClassLoader:
findLoadedClass()
loadClass()
findSystemClass()
defineClass()
String s1 = new String("Hello"); // goes to EDEN area
String s2 = "World"; // String POOL area
String s3 = "World"; // refers to existing
s2 == s3 ; // true
String s4 = new String("Hello"); // goes to EDEN area
s1 == s4; // false
System.gc();
===================================================
Relationship between Objects:
a) Generalization and Specialization
b) Realization
c) Assoication
d) Uses A
Tools of Development for Java
a) Checkstyle
checks for NamingConventions, whitespaces, comments
b) PMD and FindBugs
Coding Conventions
==> Empty Conditional Statement
if(cond){
} else {
code
}
===> Dead Code
===> Empty Catch Block
===> Copy & Paste Code
c) SONAR
d) Clover/ CodeCoverage
e) GITHub
f) Maven
g) Jenkins
https://shrib.com/#banu
Issues with VM like [ Ctrl, Caps lock]
VM terminal
without 6080
https://abc.cloudlab.jnaapti.io
terminal
login
# sudo systemctl restart jnaaptivnc
============
class Product {
Product() { new Mobile(); // PA , MA
prints PA
} new Mobile(22,"iPhone");
Product(int x) { // PA, MX
prints PX
}
}
class Mobile extends Product {
Mobile() {
//super();
prints MA
}
Mobile(int x, String a){
prints MX
}
}
=======
class Mobile extends Product {
Mobile() {
//super();
prints MA
}
==========
class Product {
new Mobile(22,"iPhone");
Product(int x) { //
prints PX
}
}
class Mobile extends Product {
Mobile() {
//super();
prints MA
}
Mobile(int x, String a){
prints MX
}
}
====================
class Product {
doTask() { prints "PTASK"}
}
class Mobile extends Product {
doTask() { prints "MTASK"}
print() { prints "MPRINT" }
}
Product p = new Mobile(); // valid ==> UPCASTING
p.doTask(); // MTASK
p.print(); // Cmpiler Error
Product[] products = new Product[5]; // Array of 4 Pointers
products[0] = new Tv(133,"Sony Bravia",135000.00,"LED");
products[1] = new Mobile(453, "MotoG", 12999.00, "4G");
products[2] = new Tv(634,"Onida Thunder",3500.00,"CRT");
products[3] = new Mobile(621, "iPhone XR", 99999.00, "4G");
products[4] = new Mobile(844, "Oppo", 9999.00, "4G");
-------
Java doesn't support multiple inheritance
Object is the super class for all objects [ Single root hierarchy]
constructor chaining super()
constrcutor chain with a class this()
class A {
A() {
}
A(int x) {
this();
}
}
============
class Product {
doTask() {
}
}
class Mobile extends Product {
doTask() {
super.doTask();
}
}
Product p = mew Mobile();
p.doTask();
===================
Access Code: visat45
Recap
-----
OOP
instance variables ==> Heap Area
static variables ==> class variables ===> Class Data ==> PermGen==>MetaSpace
local variables ==> Stack
instance variables ==> GC
Logically grouping of objects
Generalization and Specialization ==> extends ==> Inheritance
super(); constructor chaining to super class constructor
abstract class:
can't instantiate
abstract method: pure virtual function without body
All inherited class should compulstorly override this method
else the inherited class should be marked abstract
==============
public static Time addTime(Time t1, Time 2) {
}
public Time addTime(Time t) {
this and t will be used
}
==================================
Realization Relationship
========================
A Component/Object will realize the behaviour specifed by Other component/object in order to communicate
Project and Laptop can communicate with each other because
Project has specifed that the communication can happen using HDMI/ VGA
Laptop realizes it
This is done using interface
In Software Industry
UI ==> Service ==> DAO Implementation ==> database
As of Java 7:
interface interfaceName{
abstract methods
constants
}
Why program to interface?
a) DESIGN
b) IMPLEMENTATION
c) TESTING
d) INTEGRATION
interface UserDao {
void register(User user);
boolean login(User user);
}
interface Flyable {
void fly();
}
class Bird implements Flyable {
fly()
}
class Aeroplane implements Flyable {
fly()
}
============
Creating Objects:
a) If we know the class Name
obj = new ClassName();
b) We Don't know the class name, still need to create an object
String s = "java.util.Date";
Class.forName(s); //loads the Date class
Class.forName(s).newInstance();
==========================
Generic Class and interface
class Rectangle<T> { class Rectangle {
T width; Object width;
T breadth; Object breadth;
//
}
Rectangle<Integer> r1 = new Rectangle<>(4,5);
Rectangle<Dobule> r2 = new Rectangle<>(1.4,3.5);
class Node<T> {
T data;
Node<T> next;
//
}
class LinkedList<T> {
Node<T> first;
//
}
LinkedList<Employee> empList;
====================================================
Fight f = new Fight(); // ERROR
interface Dance { Fight f = new Hero();
dance(); f.fight();
} f.dance(); /ERROR
Dance d = (Dance) f;
interface Swim { d.dance();
swim();
}
interface Fight {
fight();
}
class Actor implements Dance {
dance(){}
}
class Hero extends Actor implements Fight, Swim {
fight() {} swim() {}
}
==============
Functional Interface: is an interface where in only one method
needs to be implemented
interface Flyable {
void fly();
}
class Bird implements Flyable {
public void fly() {
}
}
Flyable f = new Flyable(); // ERROR
Flyable f = new Bird();
Flyable f = new Flyable() {
public void fly() {
"jump from 10th floor!!!";
}
}
f.fly();
=================================================
Java Collection Framework
Data Containers
Array is a data container, should be the first choice
==> Size is fixed, adding/removing at arbitrary position is difficult
==> Contiguos memory
JCF provides data containers which are inter-operable.
a) interfaces
b) implementations
==> Apache
==> VAVR
c) Utility classes
class Folder implements Comparable<Folder> {
int compareTo(Folder other){
name comparision
}
}
List Set
a) supports duplicates unique
b) ordered Not
c) supports index based operation Not
get(20);
add("a", 5)
remove(5);
d) re-ordered [ sort, shuffle, reverse] Not
BAD:
List list = new ArrayList();
list.add("A");
list.add(new Date());
list.add(new Product());
List<String> list = new ArrayList<>();
list.add("A");
list.add(new Date()); // Compilation Error
==================================================
Functional Style of Programming
OOP functional style
methods function
tightly coupled to state functions are independent of state of
of object
deposit(), getBalance()
=============
High Order Functions
=> Functions which accept other functions as arguments
==> function which return a function
commonly used high order functions:
a) map
transform data
b) filter
filtering
c) reduce
aggregate
d) forEach
traverse
e) sort
terminal operations:
forEach()
reduce()
collect()
sum()
intermediary operations:
map()
filter()
limit()
skip()
flatMap()
https://rxmarbles.com/
================================================
products.stream()
products.parallelStream()
===============================================
HashSet uses hashCode() and equals() to identify duplicates
HashCode [ Numerical representation ]:
==> Two similar objects should have same hashcode
==> Two objects with different content can also have same hashcode
Map is a key/value pair
==> Dictionary
==> Registry
Map<Key,Value> map
Map<String, Double>
Map<String, List<Employee>>
============================================================================
Every exception is an object
==> What went wrong
==> Where?
==> Why?
Error and Exception types of exceptions
Error types of exceptions can't be handled during runtime
UnsatisfiedLinkError
StackOverflowError
Exception types of excetions can be handled
Exception types of Exceptions can be classified into:
a) Checked
b) Unchecked
Unchecked
Compiler doesn't enforce handling with try-catch
should be handled using conditional statements
Employee e = null;
if(e != null) {
String s = e.getName();
}
Exceptions reasons are within JRE
Checked
Compiler enforecs you to handle using try-catch
No way you can handle it with conditional statement
Reasons are outside JRE
SQLException
ClassNotFoundException
IOExcpetion
SocketException
try {
} catch(Exception ex) {
} finally {
}
============================
Compilation Errors: Code Not Reachable [ DEAD code]
try {
} catch(IOException ex) {
} catch(FileNotFoundException ex) {
}
=======================
Java Concurrent Programming ==> MultiThreaded applications
A process ==> Program in execution
A process needs at least one unit of work running
Thread is a unit of work within a process
Every Thread has a seperate Stack
Notepad, Calculator ==> Single Threaded application
Eclipse, Word, Browsers ==> Multi threaded applications
Word
Edit, SpellCheck, Grammer Check, AutoSaving
Why Multithreaded application?
a) User Experience
b) Avoid starvation
c) Optimization of available resources including CPUs
==============
Main Thread: entry point is main()
for every other user threads entry point is : run()
interface Runnable {
void run();
}
Thread class: thread control methods
a) start()
b) yield()
c) interrupt()
d) join()
e) sleep(long ms)
deprecated:
f) stop()
g) suspend()
i) resume()
http://collabedit.com/k4k72
==============================================
Thread Safety
A member is said to be thread safe if it doesn't get corrupted in
mult-threaded environment
local var --> Stack --> Each thread has a seperate stack --> Safe
instance var --> Heap --> shared by threads -> Not Safe
static var --> class data -> shared --> not Safe
Atomic variables with volatile keyword --> Safe
class SomeClass {
private volatile boolean flag = true;
}
====================
Unit Testing
Developer has to do the UnitTesting
For every class we write a test class
Account AccountTest
TCER ==> Test Case Expected Result
NO | Description | class | Method | Sample Data|expected Output| Actual |RESULT
UnitTesting Frameworks for Java:
JUnit
TestNG
=================================
Java Concurrency New APIs
Problems with legacy concurrency solutions:
a) synchronized
i) One lock per object [ instance var]
ii) one per class [ static var ]
Account
balance
profileInfo
iii) only owner can release the mutex/monitor/lock
Release when we come out of critical section or call wait()
JMX
iv) Lots of DeadLock
class BankingService {
public void transferFunds(Account fromAcc, Account toAcc, double amt) {
synchronized(fromAcc) {
synchronized(toAcc) {
update formAcc
update toAcc
insert into tx table
}
}
}
}
v) No Timeout
T1
SB105, SB106 60000
T2
SB106, SB105 89999
Rentrant locks
synchronized void doThat() {
code
doThis();
code
}
synchronized void doThis() {
}
@Roles("admin")
public void release() {
balLock.unlock();
}
With Lock APIs
class BankingService {
public void transferFunds(Account fromAcc, Account toAcc, double amt) {
if(fromAcc.balLock.tryLock(1000)) {
try{
if(toAcc.balLock.tryLock(1000)) {
try{
update formAcc
update toAcc
insert into tx table
} finally {
toAcc.balLock.unlock();
}
}
} finally {
fromAcc.balLock.unlock();
}
}
}
}
T1
SB105, SB106 60000
T2
SB106, SB105 89999
=================================================================