ATB8x Notes

4 months in Java to Better , Follow The ROADMAP.
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github.com/ create

Core Java

Why do we need Programming?

To interact with machine
to Teach machine
Communicate with machine.
Machine don't understand english.

Computers / Machine can't understand the English.

0, 1 -> switch off, switch on. - binary language.

Langage -> Translate -> Machine Language.

010101010101010101010 010101010101001 0101001010101

English , Medium Level

High Level Language

Easier for humans to read and write; abstracts hardware details.
Python ,Javascript JS, C#
Consumes more memory during execution. (Translation happends)
Easier to modify and maintain.

**Low Level Language **

Closer to machine code; less readable for humans.
Binary Language ( 0,1)
More efficient, consumes less memory.
More challenging to modify.

Major Features of Java Programming Language

Simple
Object Oriented
Platform Independent
Portable
Secure

What is Source Code?

Human understandable code written using High Level Programming language.
In java - NameOfFile.java
Source code is something that human write .
You have to follow the rules of the programming language.
Syntax - Rules that we have to follow.

**What is Byte Code? **

Source Code -> Byte Code. ( JVM Can understand) .

JVM?

Native Code

Code which NATIVE to the OS.

Compiler, Interpreter

JDK > JRE> JVM

JDK
1. Java Development Kit
  1. Complete package.
  2. Create a Java program
  3. Execute and Run also.
JRE
1. Java Runtime Environment
2. Run the Execute /Java Files.
JVM
1. Java virtual Machine
2. Execute Byte Code -> Native Code.

TOOLSet

JDK - Version ->
1. JDK different Companies
  1. Sun Microsystem, -> Oracle
  2. OS JDK (Source)- Oracle - Paid - EE - JDK EE 22 ( Extra functionality)
  3. open JDK -> FREE OS - JDK 22
  4. Amazon - JDK
  5. MS - JDK
Code Editor - Source Code.
1. Eclipse
  1. Difficult for Starter.
2. IntelliJ
  1. Professional - Paid - 30 Trial - Don't Install
  2. FREE Community Edition - Every company - - Accenture, Con.... -OS
3. VS Code - Not good for the Automation.

How to create a Program in java?

IDE - Integrated Development Environment ( Tool which can help you to write your Source Code)
JDK **Source Code -> **Code written by the Human which will converted to the machine understandable code later.

Byte Code -> Magic value which Source Code of Java is converted to ByteCode (Compiled Code) by Javac (c ,c++ ), which can be run by the JVM.

Native Code -> OS specific code, ByteCode -> Native Code, different for the different OS. windows - different, mac, different.

Source Code ->(javac) ByteCode Code -> (jvm) -> (java) Native Code

Which part of the Code is Platform Independent -> ByteCode.

Installed the IntelliJ
Installed the JDK

Java Versions

1 to 22 ->. which one we are going to use, JDK > 11 is fine

JDK -> Java Development Kit

JRE -> Java runtime environment

JVM -> Java Virtual Machine (Byte Code -> Native Code)

Java Editions

Enterprise Edition
Micro Edition
Standard Edition ( SE)
Fx

**Install the JDK **

How to check if this is installed properly?

open the CMD file ( mac, terminal)
java --version

'java~~version' is not recognized as an internal or external command,

operable program or batch file.

reason for this error is JAVA_HOME is not set.

JAVA_HOME we need to set it

C:\Program Files\Java\jdk21
Search for the Env in th task bar - Add the JAVA_HOME , system variable and user variable -

**How to Install the IDE **

Eclipse
1. Not for starters
2. IDE is little difficult to use
IntelliJ CE
1. FREE
2. OS
3. You can use this (office) - www.jetbrains.com/idea/download/?section=mac

You can install both the IntelliJ and Eclipse on a single machine.

Github.com -> Where we will upload the programs to showcase or practice

**Error **

git.exe not found, error failed...... cann't run No Such a file..

To fix this - git-scm.com/downloads

Restart the system, It will work next time.

GIT vs GITHUB

git is just protocol (rules) - version control - it is used to track the source code files.
Github.com is online platform to upload your code or repository. (showcase our project).

Package

Folder in Java
We keep the code classes here -> class ?
Sub - Package - Folder within Folder

We will Push the intial Code to GITHUB.com

create some class java -> make sure they are green color
'In top menu - git -> github -> share the project on the github.com.

**Task #1 **

JDK Installed
IntelliJ
Create a Github.com account Email. -> github.com/

Java Topics | Today

Our First Program
Keyboard Shortcuts - resources.jetbrains.com/storage/products/intellij-idea/docs/IntelliJIDEA_ReferenceCard.pdf
package - Folder Java - Where is your class or code is present.
pakacge name_of_package.

Structure of the Java Programs

Class - Blueprint
1. class Name. {
public static void main(String[] args) functions -> {}

}

Running Java program via Notepad

Create a Program with the name HelloATB.java in the notepad
Open the CMD and convert your source code -> bytecode ( .java to .class) - javac HelloATB.java
java HelloATB

Explain the main method in Java

The main method in Java is the entry point for any Java program.
public static void main(String[] - JVM seraching for the Source Code.
It is a predefined method that is executed when a Java program is run, and is required in every Java program.
public -> public toilet - - public access modifier -> visibility = everyone.
static -> we will cover later, void -> doesn't return anything , main -> name of the functions, String [] args -> String array arguments.
System.out.println("Hello World!");
We are using a println. function from the System class -> which can help to us to print the output in the console.
The main method takes an optional argument, "args".

Steps that the JVM takes to call the main method:

JVM - Class Loader Method area heap
1. Loads the necessary classes for the program. ( System, PrintStream)...
1. Locates the entry point class specified on the command line. - String[] args
1. Locates the main method in the entry point class.
1. Sets up the environment( javac) -> convert his line by line(JIT(just in time) and executes the code inside the main method. ( System.out.println("Hello World!");
When the main method completes, the JVM terminates the program.

What Happens if main() is Missing?

If a Java program does not have the main() method, it will compile but not run, because the JVM will not recognize it as the entry point.

Can the main() method be overloaded in Java?

Yes, There will be always 1 main functions rest are just clones

package sept.ex_06092024; public class Lab005 { public static void main(String[] args){ System.out.println("Hello World!"); } public static void main(String args){ System.out.println("Hello World!"); } public void main(int args){ System.out.println("Hello World!"); }

}

How do you call an overloaded main() method from another main() method?

yes, main()

Comments in Java

Single Line
Multiple Line
Keywords & Identifiers
What are the differences between keywords and identifiers in Java?
What are the most commonly used Java keywords?
How many Java keywords are currently used?

GIT Push -> Command line

SDET Club
WhatsApp Community
Email Notifications- Class Join

**Attendance **

https://forms.gle/YuhTLeNC73po2Ep27

Learning Java

Why Learn Java?
- Platform Independent
- Open Source ( Oracle) , Open JDK - OS
- Widely used
- Secure
- Robust , Portable.
- High Level Langauge

High Level Language -> Human Friendly -> Java, Python, C#

Low Level Language -> Machine Close - Binary( 1,0)

Major Features of Java Programming Language

OOps
Platform independent
Secure ( Inner class)
multi - theading
High performance

What is Source Code?

Human understandable code written using High Level Programming language is called as Source Code.
.java

How to write the Java Class?

Rule - Name of Class is same as the FileName.java
Name of class will be always - capital First letter. HelloWorld ✅
helloWorld, Not space is not.
numbers are not allowed first letter.

class FileName{

}

**What is Byte Code? **

JVM understandable code generated by Java Compiler is called as Byte Code. Byte code is also called as Magic Value.
javac - program
FileName.java -> FileName.class
Magic Value
Yes - Platform independent
What is Java Compiler? - javac

Is Java compiled or Interpreted?

Both
1. javac -> source code -> bytecode
2. java -> (jvm) -> Bytecode -> Native Code( OS)

What is JDK (Java Development Kit) / SDK (Software Development Kit)?

Java Development Kit
Create a Java programs.
Execute and Run also.
JRE and JVM
Sun Microsystem -> Oracle
1. Oracle JDK
2. Open JDK - OS source
  1. Amzon JDK
  2. MicroSoft.
  3. Azul, Eclipse (Apache foundation)

javac -> source to bytecode

java -> bytecode -> native

javap -> used to get the information about the commands in java(

javap java.util.List - help -> List , Help command get information packages.

jar -> zip file contains -> java programs -> zip ( jar) - collections of classes.

Can we have multiple version of the JDK in a same machine?

jdk 22, 21, 20 -> 1 at a time.

IntelliJ IDEA Community Edition

Mac - www.jetbrains.com/idea/download/?section=mac

Windows- www.jetbrains.com/idea/download/?section=windows

What is JRE?

Java Runtime Environment
Run the Execute /Java Files.

What is JVM?

Java virtual Machine.
Execute Byte Code -> Native Code.
Class loaders(load your class), Heap, Method area, stack.

JDK Vs JRE

Java Editions

Enterprise Edition - Servlets, JSP, JDBC etc.
Micro Edition - micro devices like Mobiles,Setup Box etc
Standard Edition - Used to develop standalone applications using applet and swing.

Java Versions

1 to 22 ->

Java Comments

Single //
Multiline
1. /*
2. */
Documentation - /** ... **/

Last Time

JAVA
JDK, JRE, JVM
basic program Java
Keywords and Identifier

Variables and Data Types

Variable - Store the value

data type variable_name = variable_value

data type
variable_name
=
variable_value

Variable Name (identifier)

Rules to follow when you define an Identifier:

Identifier can contain Alphabets, Digits, and two special symbol i.e. Dollar ($),
Underscore (_).
First character of an identifier must be an Alphabet or Dollar ($) or Underscore (_).
Keywords or Reserved words can't be used as Identifiers.

exit code 0 -> success and no error

Data type

**Primitive Data Type : **pre defined - java(guys) - they can't be broken
1. Boolean Type -> boolean - true, false
2. Numeric Type ->
  1. Integral Type -> integers (whole numbers) - Size and Max, Min Value
    1. byte : -128 to 127
    2. short
    3. int
    4. long
    5. char ( ascii, unicode) - integers
  2. Floating Point Types
    1. float
    2. double
Non Primitive Data Type 1.

**Any Ref - Bytes It can take in the memory ? | **User Defined Data types

8 Byte, 64 Bit , String s = "Pramod"
In this, s is 8 Byte, and values are stored differently.

SOP with ln and without ln

formatting

System.out.print vs ln()

String vs Char

String == Bunch of Char -
char - numeric data type (int) -> 'A'

✅ Literals

data_type variable_name = variable_value;

e.g int age = 78;

variable_value = literal

Char
Integral
Boolean
Null literal
Scientific / Exponent N Literals

✅ Operators

data_type variable_name = variable_value;

Operators are used to perform operations by using operands.
int a = 10;
data type -> int ,
variable_name -> a
operator =
literal = 10
Unary Operator
Binary Operator
Ternary Operator

// Relational Operators  = boolean
//  > < , >= <= , != , ! -> true or false

//  Compound Assignment Operators
        int a = 10;
        // += ,-= , *=, /=
//        a += 20; // a = a+ 20
//        a -= 20; // a = a - 20
//        a /= 10; // a = a/10

// Unary Operator
int a = +65; // + ->  unary operator
int b = -1;  // - -> unary operator
System.out.println(a);
System.out.println(b);
b = b+1;
System.out.println(b);

// Arithmetic Operator
// +,-,/,*
int a = 10;
int b = 2;
System.out.println(a+b); // + -> binary - 2 operands
System.out.println(a-b);
System.out.println(a*b);
System.out.println(a/b);

int age = 45;
// =  Assignment
// right value to variable

Type Casting
- Source and Destination Conversion.
Increment (++) / Decrement (--) Operators
Ternary operator.
Condition and Loops

✅ Ternary operator.

The ternary operator is a concise way to perform conditional evaluations in programming, often serving as a shorthand for if-else statements.

age > 18 -> vote india - true

age < 18 -> not allowed to vote..

Condition : anything which has some output -

Syntax Ternary in

condition ? expression_if_true : expression_if_false

✅ Conditions and Loop

If Condition
if Else
if else if, else Disadvantage of if condition
break and continue keywords

Switch ( JDK 13)

Switch is multi way branch statement.
Java switch statement executes one statement from multiple conditions.
Java switch expressions must be of byte, short, int, long(with its Wrapper type), enums and String.
case/s values are not allowed. Pramod != pramod.
The value for a case must be constant or literal. Variables are not allowed.

Advantage of the Switch

We can use the break.(break is keyword which can break out your from the loop or statement or condition.)

Syntax of Switch

switch(expression)

{

case statement 1:

code 

break;

case statement 2:

code 

break;

default statement 1: (optional)

code 

break; (optional)

}

// Condition -> If else, switch ( multiple conditions)

// Loops - For, While, Do While - Perform a task multiple times. (execute a code, statement)

For Loop

for - keyword
for( A: B:C) {}
A - Initialization
B - Condition for termination
C - Increment and Decrement - updation.

break -> break keyword, break out from the loop

continue -> do nothing and go to next iteration(skip it)

While
Take user input
- Scanner sc = new Scanner(System.in);
- int num = sc.next()

While

When you are using for statement or while statement then it verifies the condition before executing the block.
So in the case of for statement and while statement, when first time condition is false then the block will not be executed.
for and while statement are also called as Entry Controlled Loop. Do While

In the case of do-while first block of statements will be executed and then condition will be verified.

Functions

Essential building blocks that allow programmers to encapsulate code for specific tasks.
Reusable block of code is called as the functions.

Define - This is what the function will do -> block of code designed to perform a particular task.
Call - we need to calling, calling of the functions is important - executing.

Syntax of a Function

accessModifier returnType functionName(parameterType parameterName) {
    // code to be executed
    return value; // if returnType is not void
}

accessModifier: Defines the visibility of the function (e.g., public , private protected).
returnType: The data type of the value returned by the function (e.g., int , void ).
functionName: A descriptive name for the function.
parameters: Variables passed into the function.

Constructor, Method (in the part of class) - OOPs

**Types of Functions - **

No Return Type - void
Return Type - data -> Primitive or Ref Type
with Argument
without Argument

No Return Type - No Argument | 1.Without Parameters and Without Return Type

package sept.ex_30092024;

public class Lab121 {
    public static void main(String[] args) {
        for (int i = 0; i < 100 ; i++) {
            greet();
        }
    }

    // Define
    // No Return Type and No Argument
    public static void greet(){
        System.out.println("Hi");
    }
}

// Parameter == Arguments

// 1.Without Parameters and Without Return Type
// 2.Without Parameters but With Return Type
// 3.With Parameters and Without Return Type
// 4. With Parameters and With Return Type

Please Explain - Java is Object Oriented Programming - OOPs.

C -> functions - block of code.

Procedural Programming lang -

OOPs

Class

Template
Blueprint to create Objects
**Class **is a user-defined data type which defines its properties and its methods

A - Attribute

B - Behaviour

static variable, functions

constructors

Object Class

God father for the all classes.
In built functions / methods which you can use.

Main method overloading - Interview.
Object(Predefined) Class in Java
Arrays in Java
String Class
- nextLine vs next

OOps vs PPL
1. // Real life problem -> OOPs concepts

Creating - New planet ( OOPs)

// AHuman
// Attributes / properties -> 2 hand, eye color, nose, mouth, height, weight, body color, hair color
// Behaviour / methods -> walk(), eat(), talk(), read(), sleep(), hear().

Constructor

Constructor is a special method which is invoked automatically at the time of object creation.
It has the same name as the Class Name
It has no return type
Main purpose of the constructor is to initialise the instance variable values.
Parameterized Constructor - they can set or initialise the instance variable values.

// functions - perform a task , block of code
// functions within the class are called -> methods?
// class -> blueprint
// object ->  real entity created from the class. / instance of the class.
// constructor -> - special method which is invoked automatically at the time of **object creation**

Default
Parametric
Constructor Overloading
this() and Super()

Inheritance

Inherit -> Attributes and Behaviour

Child / Sub Class

Parent / Base Class

Single Inheritance -> A class inherits from a single base class.

Son extends Father

Method Overload

Same name but different para/ argument, return type.

Inheritance

Single...
Poly
1. Method Overloading
2. Method Overriding
Abstraction ( Interface) , Abtract Class
Encapsulation
1. Access Modifiers - private, public and protected.
2. Getter and Setter
Static keyword and Variable, Methods
Inner Class
Wrapper Class
Final

Encapsulation

Encapsulation helps to promote the principle of "data hiding".

Abstraction

Hiding the implementation
You hide the complete class (with data members + methods)
Abstraction can be achieved
- Abstract class
- Interfaces (Pure Abstraction)

Abstract class

Abstract is the keyword.

Remember, abstract can be a class or method both.
mean -> incomplete.
If the class doesn’t have any abstract method, then it is a concrete class.
Abstract class cannot be final.
Extend
An abstract class** cannot be instantiated** i.e. one cannot create an object of an abstract class
.Since the body of an abstract method cannot be implemented in an abstract class.
You cannot use the following modifier with abstract methods:
- Private, static, final, strictfp, synchronized, native.

Interface

interface is a keyword which is used to define User Defined Datatypes.
Instance of the interface is not possible.
Implement
Interface can contain the following members:
public final static variables public abstract methods public static inner classes

Default Methods in interfaces

Default methods are methods that can have a body.

Encapsulation

Important instance variables -> by using Methods
Getter, Setter or making them in private(Access modifiers). - Hiding the data. (data memebers)
Within the class

Rule

If parent has a param constructor extended class also will have the param constructor.
Object can't be created for the Abstract class

Static Keyword

The static keyword in Java is a non-access modifier that is primarily used for memory management and to define class-level variables and methods.

-> Static variables are variable which are created at the time of the class loading.

IIB -> Instance initialisation Block

{
    System.out.println("IIB");
    System.out.println("Here you can write a code what you want to do when Object is created");
    System.out.println("Read a MySQL db()");
}

Static Functions can't have instance variable in them.
Non Function can have static varaibles

SIB -> static initialisation Block

Variable
Block
Method
Class

ENUM

Enums, short for enumerations, are a special data type in Java.
allow you to define a collection of named constants.
Constants: Enum constants are implicitly public , static , and final . This means they cannot be changed once defined.

18/10/2024

Strings

Bunch of characters
data type used to represent sequences of characters.
Non Primitive Data Type
Class - (OOPs) - Java guys
final class String - can't change.

Immutability: Strings in Java are immutable, meaning once a string object is created, its value cannot be changed. Any modification results in the creation of a new string instance.

String name = "Pramod";

name = "Dutta";

There are now two string created in the SCP.

How to Strings are created?

= Operator -> String constant Pool(JVM)
1. String a = "amit";
2. When you create a string literal, the Java Virtual Machine (JVM) checks the "string constant pool" to see if an identical string already exists. If it does, it returns a reference to that instance; otherwise, it creates a new one.
New operator -> Heap Area -> JVM Objects
1. String name = new String("Pramod");

(==) -> Checks for the Locations in case of the String

(equals) -> Check the values

How can String be represented?

String class
StringBuffer
StringBuilder
Array of Characters
ArrayList of Characters

String Functions

Run this command in the cmd -> javap java.lang.String

Here are some of the most commonly used functions of the String class:

charAt(int index): Returns the character at the specified index in the string.

Example: "hello".charAt(0) returns 'h'.

concat(String str): Concatenates the specified string to the end of the original string.

Example: "hello".concat(" world") returns "hello world".

contains(CharSequence s): Returns true if the string contains the specified sequence of characters, otherwise false.

Example: "hello world".contains("world") returns true.

equals(Object obj): Returns true if the string is equal to the specified object, otherwise false.

Example: "hello".equals("world") returns false.

**equalsIgnoreCase(String str): **Returns true if the string is equal to the specified string, ignoring case differences, otherwise false.

Example: "HELLO".equalsIgnoreCase("hello") returns true.

**indexOf(int ch): **Returns the index of the first occurrence of the specified character in the string, or -1 if the character is not found.

Example: "hello".indexOf('l') returns 2.

length(): Returns the length of the string.

Example: "hello".length() returns 5.

replace(char oldChar, char newChar): Returns a new string resulting from replacing all occurrences of the specified oldChar with the specified newChar.

Example: "hello".replace('l', 'w') returns "hewwo".

**split(String regex): **Splits the string into an array of substrings based on the specified regular expression.

Example: "hello world".split(" ") returns ["hello", "world"].

**substring(int beginIndex, int endIndex): **Returns a new string that is a substring of the original string, starting from the specified beginIndex and ending at the endIndex (exclusive).

Example: "hello".substring(1, 3) returns "el".

toLowerCase(): Returns a new string with all characters converted to lowercase.

Example: "HELLO".toLowerCase() returns "hello".

StringBuffer and StringBuilder

Two classes used for creating mutable strings.

StringBuffer

Mutable: Unlike String , which is immutable, StringBuffer allows modifications to its content.
Thread-Safe: StringBuffer methods are synchronized, making it safe for use in multi-threaded environments. This means that multiple threads can access a StringBuffer instance without corrupting its state.

StringBuilder

Mutable: Like StringBuffer, StringBuilder allows modifications to its content.
Not Thread-Safe: StringBuilder is not synchronized, making it faster than StringBuffer in single-threaded scenarios. It is suitable for use when thread safety is not a concern.

Wrapper Class

Error Handling Exception

Arrays

Collection Framework ( DSA)

PramodDutta/Data.md

ATB8x Notes

Major Features of Java Programming Language

What is Source Code?

JDK > JRE> JVM

Java Topics | Today

Structure of the Java Programs

Explain the main method in Java

What Happens if main() is Missing?

How do you call an overloaded main() method from another main() method?

Comments in Java

Learning Java

IntelliJ IDEA Community Edition

Variables and Data Types

SOP with ln and without ln

✅ Literals

For Loop

Functions

OOPs

Constructor

Inheritance

Abstraction

Default Methods in interfaces

Strings

How to Strings are created?

String Functions

StringBuffer

StringBuilder