If Statement

Runs a specific set of code if a condition is met.
- This conditions can be anything but it primarily composed of variables such as:
  - Booleans
  - Integers
  - Floats
  - Etc...

if(condition) {

    examplecode();
    
}

If/Else Statement

Runs a specific set of code if a condition is met. OTHERWISE if the condition is not met then it runs a separate set of code.
- This conditions can be anything but it primarily composed of variables such as:
  - Booleans
  - Integers
  - Floats
  - Etc...

if(condition) {

    runprimarycodehere();

}else{

    runsecondarycodehere();

}

If/Else Example

This is an if statement testing if the variable is below 0. If it is below 0 then it prints a message stating it's negative. If it's not above 0 then it prints a message stating it's positive.

import java.util.Scanner;
Scanner scanner = new Scanner(System.in);

int number;

System.out.print("Enter a number: ");
// Get input
number = scanner.nextInt();

System.out.println(number);
// Check if number is less than 0
if(number < 0) {

    System.out.println(number + " is negative");

}else{

    System.out.println(number + " is positive");

}

Enter a number: 15
15 is positive

If-elseIf-else Statement

Runs an if statement for a condition. If the condition is met then a set of code is run. If the condition is not met then a separate if statement is run. If that condition is met then a set of code is ran but if not then the else code is run.
In this example, we made the positive negative calculator more specific. It now tests if the number is 0 first. If it is then it states that it's not negative or positive. While if it's not then it tests if the number is greater than 0 in which case it's positive. If not then it's negative.

import java.util.Scanner;
Scanner scanner = new Scanner(System.in);

int number;

System.out.print("Enter a number: ");

number = scanner.nextInt();

System.out.println(number);

//Check if number equals 0
if(number == 0) {

    System.out.println(number + " is not negative or positive");
    
//If it doesn't then check if number is greater than 0.
}else if (number > 0) {

    System.out.println(number + " is positive");

}

else {

    System.out.println(number + " is negative");

}

Enter a number: -25
-25 is negative

If/Else example with 5 or more Conditions

This is an example of a calculator that identifies if the number is positive or negative and if's it greater than or less than 100 relative to signs.

import java.util.Scanner;
Scanner scanner = new Scanner(System.in);

int number;

System.out.print("Enter a number: ");

try {
    
    // Get input
    number = scanner.nextInt();

    System.out.println(number);

    // Check if number is equal to zero
    if(number == 0) {

        System.out.println(number + " is 0");

    // If it's not then check if number is greater than 0
    }else if (number > 0) {

        if(number > 100) {

            System.out.println(number + " is positive and greater than 100");

        }
        else {

            System.out.println(number + " is positive and less than 100");

        }
    }

    // If number is less than 0...
    else if (number < 0) {

        if(number > -100) {

            System.out.println(number + " is negative and greater than -100");

        }
        else {

            System.out.println(number + " is negative and less than -100");

        }

    }

} catch (Exception e) {  
    System.out.println("Input must be an integer");
}

Enter a number: -250
-250 is negative and less than -100

Switch-case Example

In this example, we see how instead of using if statements, we use cases from inputs. We input a message and then select a number corresponding to a color. This final output then prints your message in your chosen color.

import java.util.Scanner;
Scanner scanner = new Scanner(System.in);

int number;
String message;

//Setup of COLOR variables
public static final String RED = "\u001B[31m";
public static final String GREEN = "\u001B[32m";
public static final String YELLOW = "\u001B[33m";
public static final String BLUE = "\u001B[34m";
public static final String PURPLE = "\u001B[35m";
public static final String CYAN = "\u001B[36m";
public static final String WHITE = "\u001B[37m";

// Message Input
System.out.print("Enter a message: ");
message = scanner.nextLine();
System.out.print(message + "\n\n");
// Menu for custom color.
System.out.print(RED + "0 - Red\n");
System.out.print(GREEN + "1 - Green\n");
System.out.print(YELLOW + "2 - Yellow\n");
System.out.print(BLUE + "3 - Blue\n");
System.out.print(PURPLE + "4 - Purple\n");
System.out.print(CYAN + "5 - Cyan\n");
System.out.print(WHITE + "6 - White\n\n");
System.out.print("Enter a number: ");
number = scanner.nextInt();
System.out.print(number + "\n\n");

// Switch-case related to the chosen number.
switch(number) {

    case 0:
        System.out.println(RED + message);
        break;

    case 1:
        System.out.println(GREEN + message);
        break;

    case 2:
        System.out.println(YELLOW + message);
        break;

    case 3:
        System.out.println(BLUE + message);
        break;

    case 4:
        System.out.println(PURPLE + message);
        break;

    case 5:
        System.out.println(CYAN + message);
        break;
    case 6:
        System.out.println(WHITE + message);
        break;

    }

Enter a message: This is a message

0 - Red
1 - Green
2 - Yellow
3 - Blue
4 - Purple
5 - Cyan
6 - White

Enter a number: 4

This is a message

De Morgan's Law

Not (a and b) is the same as (not a) or (not b). In Java this is written as !(a && b) == !a || !b
Not (a or b) is the same as (not a) and (not b). In Java this is written as !(a || b) == !a && !b
Or in other words it uses "nots" that are equivalent to other "not" equations.

int x = 10;
int y = 4;

if(!(x < 3) || !(y > 2) == !(x < 3 && y > 2)) {

    System.out.print("True");

}else {

    System.out.print("False");

}

True