Java Archives - codinginvent

August 5, 2024

Java Class and Object

Q:- What is Class?

In Java, a class is a blueprint or a prototype from which objects are created. A class encapsulates data for the object and methods to manipulate that data. It defines the properties (attributes) and behaviors (methods) that the objects created from the class can have.

Q:- What is object?

In Java, an object is an instance of a class. When a class is defined, no memory is allocated until an object of that class is created. Objects are the fundamental units of object-oriented programming and represent real-world entities. An object consists of:

State: Represented by attributes or fields (variables).
Behavior: Represented by methods (functions).
Identity: A unique identifier, usually the memory address where the object is stored.

Difference between object and class

Feature	Class	Object
Definition	Class is a blueprint or template from which objects are created.	Object is an instance of a class.
	Class is a logical entity.	Object is a physical entity.
	Class is a group of similar objects.	Object is a real world entity such as pen, laptop, mobile, bed, keyboard, mouse, chair etc.
Keyword	Class is declared using class keyword	Object is created through new keyword

Feature	Class	Object
Declaration	Declared once	Created as needed
Attributes & Methods	Defines structure and behavior	Has actual values and can perform behaviors
Memory Allocation	No memory allocation	Memory is allocated
Example	public class Car { … }	Car myCar = new Car(…);

Interview Questions

Question 1:- What Is a Constructor and How Do You Use It?

Answer: A constructor is a special method that is automatically called when an object is created. It is

used to initialize the object’s attributes.

Question 2:- What Is the Purpose of the new Keyword in Java?

Answer: The new keyword is used to create new objects in Java. It allocates memory for the object and

initializes it by calling the constructor.
Person p = new Person(); // Creates a new Person object

Question 3:- Write a simple Java class Calculator that has a method add which takes two integers and

returns their sum.

Answer:

public class Calculator {

// Method to add two numbers

int add(int a, int b) {

return a + b;

}

public static void main(String[] args) {

Calculator calc = new Calculator(); // Creating an object of Calculator

System.out.println(calc.add(5, 3)); // Output: 8

}

August 1, 2024

Java Operators and Control Flow Statements

Operators

Operators are special symbols used to perform operations on variables and values. Java supports several types of operators, which can be broadly classified into the following categories:

Types of operators java

Arithmetic Operators
Unary Operators
Assignment Operators
Relational Operators
Logical Operators
Bitwise Operators
Ternary Operator
Instanceof Operator

1. Arithmetic Operator

These operators are used to perform basic arithmetic operations.

+ : Addition
– : Subtraction
* : Multiplication
/ : Division
% : Modulus (remainder)

Program

public class DemoArithmeticOperator
{
  public static void main(String[] args)
  {
  int a = 10;
  int b = 5;
  System.out.println("a+b = "+ (a+b));//15
  System.out.println("a-b = "+ (a-b));//5
  System.out.println("a*b = "+ (a*b));//50
  System.out.println("a/b = "+ (a/b));//2
  System.out.println("a%b = "+ (a%b));//0
  }
}

Output :-

a+b = 15
a-b = 5
a*b = 50
a/b = 2
a%b = 0

2. Unary Operator

These operators perform operations on a single operand.

+ : Unary plus (Indicates positive value)
– : Unary minus (Negates an expression)
++ : Increment
— : Decrement
! : Logical complement (Inverts the value of a boolean)

Program

public class UnaryOperators
 {
   public static void main(String[] args) 
  {
    int a = 10;
     int b = -a; // b is -10
     a++; // a is now 11
       b--; // b is now -11
     boolean c = true;
        System.out.println(!c); // false
  }
}

Output :-

false

3. Assignment Operators

These operators are used to assign values to variables.

= : Simple assignment
+= : Add and assign
-= : Subtract and assign
*= : Multiply and assign
/= : Divide and assign
%= : Modulus and assign

program

public class AssignmentOperators {
	public static void main(String[] args)
	{
		int a = 10;
		a += 5; // a is now 15
		a -= 2; // a is now 13
		a *= 3; // a is now 39
		a /= 3; // a is now 13
		a %= 4; // a is now 1
		System.out.println(a);
	}
}

Output :-

4. Relation Operators

These operators are used to compare two values.

== : Equal to
!= : Not equal to
> : Greater than
< : Less than
>= : Greater than or equal to
<= : Less than or equal to

program

public class RelationalOperator {
	public static void main(String[] args)
	{
		int a = 10;
		int b = 5;
		System.out.println(a == b); // false
		System.out.println(a != b); // true
		System.out.println(a > b); // true
		System.out.println(a < b); // false
		System.out.println(a >= b); // true
		System.out.println(a <= b); // false
	}
}

Output :-

false
true
true
false
true
false

5. Logical Operators

These operators are used to combine multiple boolean expressions.

&& : Logical AND
|| : Logical OR
! : Logical NOT

program

package com.operator;
public class LogicalOperator
{

public static void main(String[] args) 
    {
	boolean a = true;
	boolean b = false;
	System.out.println(a && b); // false
	System.out.println(a || b); // true
	System.out.println(!a); // false
    }
}

Output :-

false
true
false

6. Bitwise Operators

These operators are used to perform bit-level operations.

& : Bitwise AND
| : Bitwise OR
^ : Bitwise XOR
~ : Bitwise Complement
<< : Left shift
>> : Right shift
>>> : Unsigned right shift

program

public class BitwiseOperator 
{
	public static void main(String[] args)
    {
    int a=5,b=7;
    System.out.println("AND " + (a & b));
    System.out.println("OR " + (a | b));
    System.out.println("XOR " + (a ^ b));
    System.out.println("Complement " + (~a));
	}
}

Let’s :-Table int a=5(0101) b=(0111)

Output :-

AND 5
OR 7
XOR 2
Complement -6

7. Ternary Operators

This is a shorthand for if-else statements. It is also known as the conditional operator.

? : : Ternary operator

program

public class TernaryOperator {
	public static void main(String[] args)
	{
		int a = 10;
		int b = 5;
		int max = (a > b) ? a : b;
		System.out.println("Max value: " + max); // 10
	}
}

Output :-

Max value: 10

8. Instanceof Operators

This operator is used to test whether an object is an instance of a specific class or subclass.

program

public static void main(String[] args)
	{
		String str = "Hello";
		boolean result = str instanceof String;
		System.out.println(result); // true
	}
}

Output :-

true

Control Flow Statements

These statements control the execution flow of a program, allowing for decision making, looping, and branching.

DECISION-MAKING STATEMENTS

These statements allow the program to make decisions based on certain conditions.

IF STATEMENT
IF-ELSE STATEMENT
IF-ELSE-IF LADDER
SWITCH STATEMENT

1. If Statement

Executes a block of code if a specified condition is true.

Syntax if Statement :-
if (condition) {
    // code to be executed if condition is true
}

program

public class If_statements
{
public static void main(String[] args)
{
	int a = 10;
	if (a > 5) {
	    System.out.println("a is greater than 5");
}
}
}

Output :-

a is greater than 5

2. If-Else Statement

Executes one block of code if a condition is true, and another block if it is false.

Syntax if else Statement :-
if (condition)
{
    // code to be executed if condition is true
else
   // code to be executed if condition is true
}

program

public class If_Else_statements
{
	public static void main(String[] args)
	{
		int a = 10;
		if (a > 20) {
		    System.out.println("a is greater than 20");
		} else {
		    System.out.println("a is not greater than 20");
		}
	}
}

Output :-

a is not greater than 20

3. if-else-if Ladder

Allows for multiple conditions to be checked sequentially.

program

public class If_else_If_Ladder
{
public static void main(String[] args)
{
	int a = 10;
	if (a > 10) {
	    System.out.println("a is greater than 10");
	} else if (a == 10) {
	    System.out.println("a is equal to 10");
	} else {
	    System.out.println("a is less than 10");
	}
}
}

Output :-

a is equal to 10

4. Switch Statements

Allows for a variable to be tested for equality against a list of values.

Syntax:-
switch (expression) 
{
    case value1:
        // code to be executed if expression == value1
        break;
    case value2:
        // code to be executed if expression == value2
        break;
    // you can have any number of case statements
    default:
        // code to be executed if expression doesn't match any case
}

program

public class Switch_Statements {
	public static void main(String[] args)
	{
		int day = 3;
		switch (day) {
		    case 1:
		        System.out.println("Monday");
		        break;
		    case 2:
		        System.out.println("Tuesday");
		        break;
		    case 3:
		        System.out.println("Wednesday");
		        break;
		    default:
		        System.out.println("Other day");
		        break;
		}
	}
}

Output :-

Wednesday

trtrt
rtrtrtrt

August 1, 2024

Java Installation

Java Architecture

Java Development Kit (JDK):

The JDK provides tools needed to write Java programs, including the compiler javac, and tools like java (the interpreter) and javadoc.

Java Runtime Environment (JRE):

The JRE provides the libraries, Java Virtual Machine (JVM), and other components to run applications written in Java.

Java Virtual Machine (JVM):

The JVM is an abstract machine that enables your computer to run a Java program. When you run a Java program, the JVM translates the Java bytecode into native machine code.

ONLINE EDITORS OF JAVA

JDoodle

Website: JDoodle
Features: Supports multiple languages, allows sharing code snippets, has a collaborative mode for real-time coding with others.

Repl.it

Website: Repl.it
Features: Supports many languages, includes an integrated development environment (IDE), allows for real-time collaboration, and can deploy applications.

OnlineGDB

Website: OnlineGDB
Features: Supports debugging, offers multiple programming languages, includes a basic IDE, and allows you to save and share code.

OFFLINE EDITORS OF JAVA

Eclipse

Website: Eclipse
Features: Comprehensive IDE, strong plugin ecosystem, supports multiple languages, integrated debugging, and version control systems (VCS) integration.

IntelliJ IDEA

Website: IntelliJ IDEA
Features: Advanced code completion, intelligent refactoring, integrated VCS, built-in tools for web and enterprise development, and a large plugin repository. The Community Edition is free and open-source, while the Ultimate Edition is commercial.

Visual Studio Code (VS Code)

Website: VS Code
Features: Lightweight and highly customizable, supports Java through extensions (e.g., Java Extension Pack), integrated terminal, and VCS support.

For Windows

Step 1: Install Java JDK

Download the JDK:
- Go to the Oracle JDK download page.
- Download the installer for the latest version of JDK.

Install the JDK:

Run the downloaded installer.

Follow the installation wizard and complete the installation process.

By default, JDK will be installed in C:\Program Files\Java\jdk-[version].

Set up Environment Variables:

Right-click on This PC or My Computer and select Properties.

Click on Advanced system settings.

Click on Environment Variables.

Under System variables, click New and add a new variable:

Variable name: JAVA_HOME

Variable value: C:\Program Files\Java\jdk-[version]

Find the Path variable in the System variables section and click Edit.

Click New and add %JAVA_HOME%\bin.

Click OK to save the changes.

Step 2: Install STS

Spring Tool Suite (STS) is an Eclipse-based IDE that provides a superset of the Java EE distribution of Eclipse. Here are the steps to install STS:

Step 1: Download STS

Visit the STS Download Page:
- Go to the Spring Tool Suite download page.
Select the Version:
- Choose the appropriate version for your operating system (Windows, macOS, Linux).

Step 2: Install STS

For Windows:

Extract the Downloaded ZIP File:
- Locate the downloaded ZIP file (e.g., spring-tool-suite-4-4.x.x.RELEASE-e4.x-win32.win32.x86_64.zip).
- Extract the contents to your desired installation directory.
Run STS:
- Navigate to the extracted folder and find the SpringToolSuite4.exe file.
- Double-click to launch STS.

August 1, 2024

Data Types & Variables

Java First Program

 public class Main
{
   public static void main(String[] args)
   {
      System.out.println("Hello World");
   }
}

Java Comments

Comments can be used to explain Java code, and to make it more readable. It can also be used to prevent execution when testing alternative code.

Java single-line Comments

Single-line comments start with two forward slashes (//).

This example uses a single-line comment before a line of code:

Java multi-line Comments

Multi-line comments start with /* and ends with */.

Example

/* The code below will print the words Hello World

to the screen, and it is amazing */ System.out.println(“Hello World”);

Java Variables

Variables are containers for storing data values.

In Java, there are different types of variables, for example:

Variables Declaration and Initialization

Declaration: This involves specifying the data type and the variable name.
Initialization: This involves assigning a value to the variable.

// Declarationint a; // Initialization a = 10; // Declaration and Initializationint b = 20;

Types of Variables in Java

Variables Local Variables
Instance Variables
Static (Class)

Local Variables

Declared inside a method, constructor, or block.
Created when the method, constructor, or block is entered and destroyed once exited.
Scope is limited to the method, constructor, or block.

Instance Variables

Declared inside a class but outside any method, constructor, or block.
Created when an object is created and destroyed when the object is destroyed.
Instance variables are unique to each instance of a class.

Static (Class) Variables

Declared with the static keyword inside a class, outside any method, constructor, or block.
Created when the program starts and destroyed when the program stops.
Shared among all instances of a class.

Java Data Types

In Java, data types specify the size and type of values that can be stored in variables. Java supports two categories of data types:

1. Primitive Data Types

Introduction

Java supports eight built-in data types known as primitive data types.
Primitive data types are predefined by the language and named by a keyword.

Categories of Primitive Data Types

Integer Types
Floating-Point Types
Character Type
Boolean Type

Integer Types

byte

Size: 8-bit
Range: -128 to 127

short

Size: 16-bit
Range: -32,768 to 32,767

int

Size: 32-bit
Range: -2^31 to 2^31 – 1

long

Size: 64-bit
Range: -2^63 to 2^63 – 1

Floating-Point Types

float
- Size: 32-bit
- Single-precision
double
- Size: 64-bit
- Double-precision

boolean

Size: Not precisely defined (depends on JVM)

Values: true or false

Character Type

char
- Size: 16-bit
- Represents a single 16-bit Unicode character
- Range: ‘\u0000’ (0) to ‘\uffff’ (65,535)

Default Values

byte: 0
short: 0
int: 0
long: 0L
float: 0.0f
double: 0.0d
char: ‘\u0000’
boolean: false

2. Non-Primitive Data Types

Introduction

Non-primitive data types, also known as reference types, refer to objects.
Unlike primitive types, non-primitive types are created by the programmer.

Categories of Non Primitive Data Types

Strings
Arrays
Classes
Interfaces
Collections

Strings

A sequence of characters.
Defined using the String class.
Immutable: once created, their values cannot be changed.

public class StringExample 
{ 
    public static void main(String[] args)
     { 
       String str = "Hello, World!"; 
       System.out.println(str); 
     }
}

Arrays

A collection of elements of the same type.
Fixed in size once created.
Can be one-dimensional or multi-dimensional.

public class ArrayExample
 {
      public static void main(String[] args)
    {
       int[] arr = {1, 2, 3, 4, 5}; for (int num : arr) 
       { 
          System.out.println(num);
        }
     }
 }

Classes

Blueprint for creating objects.
Contains fields (variables) and methods to define behaviors.

class Dog 
{
    String breed;
    int age;
    void bark()
    {
        System.out.println("Woof!");
    }
}


public class ClassExample 
{
    public static void main(String[] args)
    {
        Dog myDog = new Dog();
        myDog.breed = "Golden Retriever";
        myDog.age = 5;
        myDog.bark();
        System.out.println("Breed: " + myDog.breed + ", Age: " + myDog.age);
    }
}

Interview Questions

Q-1:- What is type casting? Explain with an example.

A-1:- Type casting is converting a variable from one data type to another. There are two

types of casting in Java:

Q-2:- What is the difference between float and double?

A-2:- float: Single precision (32 bits), approximately 6-7 decimal digits.

double: Double precision (64 bits), approximately 15-16 decimal digits.

Q-3:- What are the major differences in data types between Java and JavaScript?

A-3:- Java has strong and static typing. Data types must be declared explicitly, and type

checking is done at compile-time. Examples include int, double, char, boolean,

String.

JavaScript has dynamic typing. Variables can hold any type of data, and types are

checked at runtime. Examples include number, string, boolean, object,

undefined, null.

JAVA MCQ

Q-1:- What is the default value of a local variable in Java?

A) 0

B) null

C) false

D) No default value

Q-2:- Which of the following is not a primitive data type in Java?

A) int

B) float

C) String

D) boolean

Q-3:- Which of the following is not a keyword in Java?

A) static

B) Boolean

C) void

D) private

August 1, 2024

Introduction to Java Programming

Java is a powerful and widely-used programming language that is based on object-oriented principles. Developed by Sun Microsystems in 1995, it remains one of the most popular programming languages today. Java is utilized for web applications, mobile apps (Android), and enterprise-level solutions.

Why Learn Java?

Java is a versatile language that is ideal for beginners due to its simple and easy-to-understand syntax. Key features of Java include platform independence (Write Once, Run Anywhere), robust memory management, and a comprehensive standard library. Learning Java can open up career opportunities in enterprise-level applications and Android development.

Key Concepts of Java

Java programming is based on several fundamental concepts:

Object-Oriented Programming (OOP): Java follows OOP principles, including classes, objects, inheritance, polymorphism, and encapsulation.
Syntax: Java’s syntax is similar to C++, making it easier to understand if you have prior knowledge of C++ or a similar language.
Memory Management: Java uses automatic garbage collection to manage memory, which helps prevent memory leaks and inefficient memory usage.

Getting Started with Java

To start with Java programming, you need to install the Java Development Kit (JDK). You can use Integrated Development Environments (IDEs) such as IntelliJ IDEA, Eclipse, or NetBeans for coding and debugging. Starting with basic Java programs like “Hello World” and gradually working on more complex projects is an effective way to learn.

Conclusion

Learning Java provides a strong foundation that can lead to opportunities in various fields, including software development, web development, and mobile application development. Regular practice and working on real-world projects will enhance your skills and help you become a proficient Java programmer.

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Category: Java

Q:- What is Class?

Difference between object and class

Operators

Types of operators java

1. Arithmetic Operator

Program

Output :-

2. Unary Operator

Program

Output :-

3. Assignment Operators

program

Output :-

4. Relation Operators

program

Output :-

5. Logical Operators

program

Output :-

6. Bitwise Operators

program

Let’s :-Table int a=5(0101) b=(0111)

Output :-

7. Ternary Operators

program

Output :-

8. Instanceof Operators

program

Output :-

Control Flow Statements

DECISION-MAKING STATEMENTS

1. If Statement

program

Output :-

2. If-Else Statement

program

Output :-

3. if-else-if Ladder

program

Output :-

4. Switch Statements

program

Output :-

Java Architecture

Java Development Kit (JDK):

Java Runtime Environment (JRE):

Java Virtual Machine (JVM):

ONLINE EDITORS OF JAVA

OFFLINE EDITORS OF JAVA

For Windows

Step 1: Install Java JDK

Step 2: Install STS

Step 1: Download STS

Step 2: Install STS

For Windows:

Java First Program

Java Comments

Java single-line Comments

Java multi-line Comments

Example

Java Variables

Variables Declaration and Initialization

// Declarationint a; // Initialization a = 10; // Declaration and Initializationint b = 20;

Types of Variables in Java

Local Variables

Instance Variables

Static (Class) Variables

Java Data Types

1. Primitive Data Types

Introduction

Categories of Primitive Data Types

Integer Types

Floating-Point Types

boolean

Size: Not precisely defined (depends on JVM)

Character Type

Default Values