Java Essentials
Java JDK, JRE and JVM
JVM (Java Virtual Machine) is an abstract machine that enables your computer to run a Java program.

JRE (Java Runtime Environment) is a software package that provides Java class libraries, Java Virtual Machine (JVM), and other components that are required to run Java applications.
JDK (Java Development Kit) is a software development kit required to develop applications in Java. When you download JDK, JRE is also downloaded with it.
What is JDK?
JDK (Java Development Kit) is a software development kit required to develop applications in Java. When you download JDK, JRE is also downloaded with it.
In addition to JRE, JDK also contains a number of development tools (compilers, JavaDoc, Java Debugger, etc).

If you want to develop Java applications, download JDK.
Relationship between JVM, JRE, and JDK.

Java Operators
Operators in Java can be classified into 5 types:
Arithmetic Operators
Assignment Operators
Relational Operators
Logical Operators
Unary Operators
Bitwise Operators
Arithmetic Operator
+
Addition
-
Subtraction
*
Multiplication
/
Division
%
Modulo Operation (Remainder after division)
Logical Operators
~
Bitwise Complement
<<
Left Shift
>>
Right Shift
>>>
Unsigned Right Shift
&
Bitwise AND
^
Bitwise exclusive OR
Java Unary Operators
+
Unary plus: not necessary to use since numbers are positive without using it
-
Unary minus: inverts the sign of an expression
++
Increment operator: increments value by 1
--
Decrement operator: decrements value by 1
!
Logical complement operator: inverts the value of a boolean
Java Assignment Operators
=
a = b;
a = b;
+=
a += b;
a = a + b;
-=
a -= b;
a = a - b;
*=
a *= b;
a = a * b;
/=
a /= b;
a = a / b;
%=
a %= b;
a = a % b;
Java Relational Operators
=
a = b;
a = b;
+=
a += b;
a = a + b;
-=
a -= b;
a = a - b;
*=
a *= b;
a = a * b;
/=
a /= b;
a = a / b;
%=
a %= b;
a = a % b;
Java Logical Operators
&&
(Logical AND)
expression1 && expression2
true
only if both expression1 and expression2 are true
||
(Logical OR)
expression1 || expression2
true
if either expression1 or expression2 is true
!
(Logical NOT)
!expression
true
if expression is false
and vice versa
Java Bitwise Operators
~
Bitwise Complement
<<
Left Shift
>>
Right Shift
>>>
Unsigned Right Shift
&
Bitwise AND
^
Bitwise exclusive OR
Java Basic Input and Output
Java Output
System.out.println(); or
System.out.print(); or
System.out.printf();
Java Input
import java.util.Scanner;
// create an object of Scanner
Scanner input = new Scanner(System.in);
// take input from the user
int number = input.nextInt();
Java Flow Control
Java if...else Statement
Working of if Statement

How the if...else statement works?

How the if...else...if ladder works?

class Main {
public static void main(String[] args) {
int number = 0;
// checks if number is greater than 0
if (number > 0) {
System.out.println("The number is positive.");
}
// checks if number is less than 0
else if (number < 0) {
System.out.println("The number is negative.");
}
// if both condition is false
else {
System.out.println("The number is 0.");
}
}
}
Output
The number is 0.
Java switch Statement
switch (expression) {
case value1:
// code
break;
case value2:
// code
break;
...
...
default:
// default statements
}
Java for Loop

for-each Loop Sytnax
// print array elements
class Main {
public static void main(String[] args) {
// create an array
int[] numbers = {3, 9, 5, -5};
// for each loop
for (int number: numbers) {
System.out.println(number);
}
}
}
/* Output
3
9
5
-5
*/
Java while loop
while (testExpression) {
// body of loop
}


do {
// body of loop
} while(textExpression);
Break Statement
How break statement works?

if (number < 0.0) {
break;
}
Java break and Nested Loop

Labeled break Statement

Java continue Statement
Working of Java continue statement

Java continue with Nested Loop.

Java continue with Nested Loop

Labeled continue Statement

Java Arrays
String[] array = new String[100];
// declare arrray
dataType[] arrayName;
// declare an array
int[] age = new int[5];
// initialize array
age[0] = 12;
age[1] = 4;
age[2] = 5;
..

int[][] a = new int[3][4];
Here, we have created a multidimensional array named a. It is a 2-dimensional array, that can hold a maximum of 12 elements,

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