If Statements

If a code statement is true then the code within the if statement block will execute. The example below uses user input and an if statement to guess what color the question is in.

import java.util.Scanner;
import java.io.*;

public class Main {
    public static void main(String[] args){
        Scanner userQuestion = new Scanner(System.in); // Gets user input using Scanner
        System.out.println("\u001B[34m" + "What color is this text?");

        String colorGuess = userQuestion.nextLine(); // Sets user input equal to new variable colorGuess
        System.out.print("Your guess is: " + colorGuess);
        
        if (colorGuess.equalsIgnoreCase("blue")) { // Uses String method equalsIgnoreCase to check if the two strings are identical. The result is a boolean expression that if true will execute the if statement.
            System.out.print(" which is correct!"); // When the answer is correct, this statement is printed
        }
}
}
Main.main(null);

What color is this text?
Your guess is: blue which is correct!

If-Else Statements

If the code statement in the if is true then the code within the the if statement will execute. If the code statement in the if is false then the code within the else statement will execute. The example below uses if and else statements to check if the response to a question is correct or not.

import java.util.Scanner;
import java.io.*;

public class Main {
    public static void main(String[] args){
        Scanner userQuestion = new Scanner(System.in); // Gets user input using Scanner
        System.out.println("\u001B[34m" + "What color is this text?");

        String colorGuess = userQuestion.nextLine(); // Sets user input equal to new variable colorGuess
        System.out.print("Your guess is: " + colorGuess);
        
        if (colorGuess.equalsIgnoreCase("blue")) { // Uses String method equalsIgnoreCase to check if the two strings are identical. The result is a boolean expression that if true will execute the if statement.
            System.out.print(" which is correct!"); // When the answer is correct, this statement is printed
        }

        else {
            System.out.print(" which is incorrect!"); // If the statement is incorrect, the else statement will execute and tell the user that their answer is incorrect. 
        }
}
}
Main.main(null);

What color is this text?
Your guess is: yellow which is incorrect!

If-Else-If-Else Statements

This option of conditionals is helpful if there are multiple options that are correct. If the code statement in the if is true, then the code segment under the if statement will execute. If the code statement in the if is false, then the code segment in the else if statement will execute if it is true. If the code segment in the else if statement is false, then the code segment in the else statement will execute.

import java.util.Scanner;
import java.io.*;

public class Main {
    public static void main(String[] args){
        Scanner userQuestion = new Scanner(System.in); // Gets user input using Scanner
        System.out.println("\u001B[34m" + "What color is this text?");

        String colorGuess = userQuestion.nextLine(); // Sets user input equal to new variable colorGuess
        System.out.print("Your guess is: " + colorGuess);
        
        if (colorGuess.equalsIgnoreCase("blue")) { // Uses String method equalsIgnoreCase to check if the two strings are identical. The result is a boolean expression that if true will execute the if statement.
            System.out.print(" which is correct!"); // When the answer is correct, this statement is printed
        }

        else if (colorGuess.equalsIgnoreCase("cyan")) {
            System.out.print(" which is correct!"); // This is another possible correct answer, so this statement will be printed if the user does not guess "blue"
        }

        else {
            System.out.print(" which is incorrect!"); // If the statement is incorrect, the else statement will execute and tell the user that their answer is incorrect. 
        }
}
}
Main.main(null);

What color is this text?
Your guess is: cyan which is correct!

If, Else, ElseIf Statements versus Switch Cases

Below is the same code segment, but expanded with more color options. The first code block uses if, else, and else if statements. The bottom code block uses switch cases.

import java.util.Scanner;
import java.io.*;

public class Main {
    public static void main(String[] args){
        Scanner userQuestion = new Scanner(System.in); // Gets user input using Scanner
        System.out.println("\u001B[34m" + "What color is this text?");

        String colorGuess = userQuestion.nextLine(); // Sets user input equal to new variable colorGuess
        System.out.print("Your guess is: " + colorGuess);
        
        if (colorGuess.equalsIgnoreCase("blue")) { // Uses String method equalsIgnoreCase to check if the two strings are identical. The result is a boolean expression that if true will execute the if statement.
            System.out.print(" which is correct!"); // When the answer is correct, this statement is printed
        }

        else if (colorGuess.equalsIgnoreCase("cyan")) {
            System.out.print(" which is correct!"); // This is another possible correct answer, so this statement will be printed if the user does not guess "blue"
        }

        else if (colorGuess.equalsIgnoreCase("red")) {
            System.out.print(" which is incorrect!"); // This is another possible incorrect answer, so this statement will be printed if the user does not guess "blue"
        }

        else if (colorGuess.equalsIgnoreCase("green")) {
            System.out.print(" which is incorrect!"); // This is another possible incorrect answer, so this statement will be printed if the user does not guess "blue"
        }

        else if (colorGuess.equalsIgnoreCase("yellow")) {
            System.out.print(" which is incorrect!"); // This is another possible incorrect answer, so this statement will be printed if the user does not guess "blue"
        }

        else if (colorGuess.equalsIgnoreCase("torquise")) {
            System.out.print(" which is correct!"); // This is another possible correct answer, so this statement will be printed if the user does not guess "blue"
        }

        else if (colorGuess.equalsIgnoreCase("orange")) {
            System.out.print(" which is incorrect!"); // This is another possible incorrect answer, so this statement will be printed if the user does not guess "blue"
        }

        else {
            System.out.print(" which is incorrect!"); // If the statement is incorrect, the else statement will execute and tell the user that their answer is incorrect. 
        }
}
}
Main.main(null);

What color is this text?
Your guess is: purple which is incorrect!

public class Main {
    public static void main(String[] args){
        Scanner userQuestion = new Scanner(System.in); // Gets user input using Scanner
        System.out.println("\u001B[34m" + "What color is this text?");

        String colorGuess = userQuestion.nextLine(); // Sets user input equal to new variable colorGuess
        System.out.print("Your guess is: " + colorGuess);
        String response;

        switch (colorGuess) { // Depending on what the user guesses, the case that matches the color guessed will execute.
            case "blue":
                response = " which is correct!";
                break;
            case "cyan":
                response = " which is correct!";
                break;
            case "purple":
                response = " which is incorrect!";
                break;
            case "turquise":
                response = " which is correct!";
                break;
            case "yellow":
                response = " which is incorrect!";
                break;
            case "red":
                response = " which is incorrect!";
                break;
            case "green":
                response = " which is incorrect!";
                break;
            case "orange":
                response = " which is incorrect!";
                break;               
            default:
                response = " which is not a valid response!";
                break;  
        } 
        System.out.print(response);
    }
}

Main.main(null)

What color is this text?
Your guess is: green which is incorrect!

De Morgan's Law

De Morgan's law shows how numbers are related through their opposites. According to De Morgan's Law logic, "the complement of the union of two sets is equal to the intersection of their separate complements." In code the definition is "if two (or more) input variables are AND’ed and negated, it should be equivalent to the OR of the complements of the individual input variables"

public class Main {
    public static void main(String[] args){
        boolean a = false;
        boolean b = false;

        if (!(a&&b)){
            System.out.println("a = " + a);
            System.out.println("b = " + b);
            System.out.println("Test 1: True");
        }

    }
}

Main.main(null)

a = false
b = false
Test 1: True

public class Main {
    public static void main(String[] args){
        boolean a = false;
        boolean b = false;

        if (!a || !b){
            System.out.println("a = " + a);
            System.out.println("b = " + b);
            System.out.println("Test 2: True");
        }
    }
}

Main.main(null)

a = false
b = false
Test 2: True