Java Essentials Code Notes
import java .util .Scanner ;
public class HelloJava {
public static void main (String [] args ) {
// Printing
System .out .println ("Hello World !!\n New Line !!" );
// Variables
int score = 6 ; // Declare and Initialize
score = score + 1 ; // Update variable
System .out .println ("Your score: " + score ); // Your score: 7
double studentGrade = 88.8 ;
String name = "Mosaad Sallam" ;
System .out .println (name + " : " + studentGrade ); // Mosaad Sallam : 88.8
long views = 3_000_000_000L ;
float price = 50.99F ;
char answer = 'A' ;
boolean isRaised = false ;
double result = 10 % 3 ; // 1
int x = 1 , y ;
y = ++x ; // Postfix x=2 y=2 Score
x += 2 ; // x = x + 2
// Casting in JAVA
long a = 5 ;
int b = (int ) a ;
System .out .println (b ); // 5
// Salary Program
String salaryDetails =
"Salary details :" +
"\n ------------------" +
"\n Your base salary : " + a +
"\n Taxes : " + b +
"\n Salary after taxes : " + (x - y ) +
"\n Incentive : " + score +
"\n --------------------" +
"\n Net salary : " + price ;
System .out .println (salaryDetails );
// If-else Statement
int number1 = 1 ;
if (number1 > 0 ) {
System .out .println ("The number is positive." );
} else {
System .out .println ("The number is not positive." );
}
System .out .println ("Statement outside if...else block" );
// Operators
// Arithmetic Operators
int e = 12 , f = 5 ;
System .out .println ("a + b = " + (e + f ));
System .out .println ("a - b = " + (e - f ));
System .out .println ("a * b = " + (e * f ));
System .out .println ("a / b = " + (e / f ));
System .out .println ("a % b = " + (e % f ));
// Assignment Operators
int g = 4 , lol ;
lol = g ;
System .out .println ("Var using =: " + lol );
lol += g ;
System .out .println ("Var using +=: " + lol );
lol *= g ;
System .out .println ("Var using *=: " + lol );
// Relational Operators
int h = 7 , j = 11 ;
System .out .println ("a is " + a + " and b is " + b );
System .out .println (h == j ); // false
System .out .println (h != j ); // true
System .out .println (h > j ); // false
System .out .println (h < j ); // true
System .out .println (h >= j ); // false
System .out .println (h <= j ); // true
// Logical Operators
System .out .println ((5 > 3 ) && (8 > 5 )); // true
System .out .println ((5 > 3 ) && (8 < 5 )); // false
System .out .println ((5 < 3 ) || (8 > 5 )); // true
System .out .println ((5 > 3 ) || (8 < 5 )); // true
System .out .println ((5 < 3 ) || (8 < 5 )); // false
System .out .println (!(5 == 3 )); // true
System .out .println (!(5 > 3 )); // false
// Unary Operators
int l = 12 , z = 12 ;
int result1 , result2 ;
System .out .println ("Value of a: " + l );
result1 = ++l ;
System .out .println ("After increment: " + result1 );
System .out .println ("Value of b: " + z );
result2 = --z ;
System .out .println ("After decrement: " + result2 );
// Java instanceof Operator
String str = "Programiz" ;
boolean isString ;
isString = str instanceof String ;
System .out .println ("Is str an object of String? " + isString );
// switch-case
int num = 44 ;
String size ;
switch (num ) {
case 29 :
size = "Small" ;
break ;
case 42 :
size = "Medium" ;
break ;
case 44 :
size = "Large" ;
break ;
case 48 :
size = "Extra Large" ;
break ;
default :
size = "Unknown" ;
break ;
}
System .out .println ("Size: " + size );
// Getting Input
Scanner input = new Scanner (System .in );
System .out .print ("Enter float: " );
float myFloat = input .nextFloat ();
System .out .println ("Float entered = " + myFloat );
System .out .print ("Enter double: " );
double myDouble = input .nextDouble ();
System .out .println ("Double entered = " + myDouble );
System .out .print ("Enter text: " );
String myString = input .next ();
System .out .println ("Text entered = " + myString );
// Java Arrays
String [] array = new String [100 ];
double [] data ;
data = new double [10 ];
double [] dataArray = new double [10 ];
int [] ageArray = {12 , 4 , 5 , 2 , 5 }; // Declare, Initialize, and Access
System .out .println ("Accessing Elements of Array:" );
for (int i = 0 ; i < ageArray .length ; i ++) {
System .out .println ("Element at index " + i + ": " + ageArray [i ]);
}
// Compute Sum and Average of Array Elements
int [] numbersArray = {2 , -9 , 0 , 5 , 12 , -25 , 22 , 9 , 8 , 12 };
int sumArray = 0 ;
double averageArray ;
for (int numArray : numbersArray ) {
sumArray += numArray ;
}
int arrayLength = numbersArray .length ;
averageArray = ((double ) sumArray / arrayLength );
System .out .println ("Sum = " + sumArray ); // Sum = 36
System .out .println ("Average = " + averageArray ); // Average = 3.6
// Create a 2D array
int [][] array2D = {
{1 , 2 , 3 },
{4 , 5 , 6 , 9 },
{7 },
};
System .out .println ("Length of row 1: " + array2D [0 ].length );
System .out .println ("Length of row 2: " + array2D [1 ].length );
System .out .println ("Length of row 3: " + array2D [2 ].length );
// Copying arrays
int [] numbersCopy = {1 , 2 , 3 , 4 , 5 , 6 };
int [] positiveNumbers = numbersCopy .clone (); // Copying arrays
for (int numCopy : positiveNumbers ) {
System .out .print (numCopy + ", " );
}
}
}