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JAVA QUICK REVISION NOTES

Hello everyone I am RAUSHAN RANJAN

In this post you are going to get all the neccessary that you need to learn in java. You don't need to search other places to get the exact detail. 

I know many of you are new in programming. Don't worry, you will get every minor details that is required to understand java from Basics.



Let's jump into the topic

    1. DATA TYPES:

Data types specify the type of data that a variable can store. In Java, there are two main categories of data types:

a. Primitive Data Types:

  • byte: represents a 1-byte integer (-128 to 127).
  • short: represents a 2-byte integer (-32,768 to 32,767).
  • int: represents a 4-byte integer (-2,147,483,648 to 2,147,483,647).
  • long: represents an 8-byte integer (-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807).
  • float: represents a 4-byte floating-point number with decimal precision.
  • double: represents an 8-byte floating-point number with higher decimal precision.
  • boolean: represents a boolean value (true or false).
  • char: represents a single character.

b. Reference Data Types:

  • Arrays: represents a collection of elements of the same type.
  • String: represents a sequence of characters.

Example:

int age = 25;

double salary = 50000.50;

boolean isStudent = true;

String name = "John Doe";

int[] numbers = {1, 2, 3, 4, 5};


    2. VARIABLES:

Variables are used to store data in a program. In Java, variables must be declared with a specific data type before they can be used.

Example:

int num1; // Declaration

num1 = 10; // Assignment 

int num2 = 20; // Declaration and assignment in one line


    3. OPERATORS:

Operators are used to perform operations on variables and values. Java supports various types of operators, including:

  • Arithmetic Operators: +, -, *, /, % (remainder)
  • Assignment Operators: =, +=, -=, *=, /=, %=
  • Comparison Operators: ==, !=, >, <, >=, <=
  • Logical Operators: && (AND), || (OR), ! (NOT)
  • Increment/Decrement Operators: ++, --
  • Bitwise Operators: &, |, ^ (XOR), ~ (NOT), << (left shift), >> (right shift)

Example:

int a = 10, b = 5;

int sum = a + b;

int product = a * b;

boolean result = (a > b) && (a != b);


    4. CONDITIONAL STATEMENTS (if-else):

Conditional statements allow the execution of different blocks of code based on certain conditions. The most common conditional statement is the if-else statement.

Example:

int age = 18;

if (age >= 18) {

    System.out.println("You are eligible to vote.");

} else {

    System.out.println("You are not eligible to vote.");

}

    5. LOOPS:

Loops are used to repeat a block of code multiple times. Java provides three main types of loops:

a. for Loop:

for (int i = 1; i <= 5; i++) {

    System.out.println(i);

}

b. while Loop:

int i = 1;

while (i <= 5) {

    System.out.println(i);

    i++;

}

c. do-while Loop:

int i = 1;

do {

    System.out.println(i);

    i++;

} while (i <= 5);

    6. SWITCH-CASE:

The switch case statement is used to perform different actions based on different values of a variable or an expression.

Example:

int day = 1;

String dayName;

switch (day) {

    case 1:

        dayName = "Sunday";

        break;

    case 2:

        dayName = "Monday";

        break;

    // ... more cases

    default:

        dayName = "Invalid day";

}

System.out.println("Day: " + dayName);

    7. FUNCTIONS/METHODS:

Functions or methods are blocks of code that can be called to perform a specific task. They are used to organize code and make it reusable.

Example:

// Method that calculates the sum of two numbers

public static int sum(int num1, int num2) {

    return num1 + num2;

}

// Calling the method

int result = sum(10, 20);

System.out.println("Sum: " + result);

These explanations, along with the provided examples, should give you a solid understanding of these fundamental concepts in Java programming. Remember to practice and experiment with code to further enhance your skills.

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