Syntax of the ternary conditional operator:

boolean-expression ? expression1 : expression2

If boolean-expression evaluates to true, the result is expression1; otherwise, the result is expression2.

Example 1: Finding the maximum of two numbers

max = (num1 > num2) ? num1 : num2;

Example 2: Checking if a number is even or odd

System.out.print((numb % 2 == 0) ? "an even number" : "not an even number");

Note: The ternary operator allows you to write shorter and more concise code compared to traditional if-else statements.

Important: The switch statement allows you to select one action from multiple possibilities based on the value of an expression. It is an alternative to multiple nested if-else constructs, especially useful when you need to check many conditions.

Basic form:

switch (variable_or_expression) {
    case value1:
        // Actions for case 1
        break;
    case value2:
        // Actions for case 2
        break;
    default:
        // Default action if no case matches
}

Important Notes:

• ▶ The default block executes when none of the other blocks match.
• ▶ The break keyword causes control to jump to the end of the switch after processing the block. If you omit break, execution will continue to the next case (fall-through).

Example with integer:

public class SwitchExample {
    public static void main(String[] args) {
        int day = 3;
        
        switch(day) {
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            default:
                System.out.println("Unknown Day");
        }
    }
}

Result: Wednesday

Example with String (Java 7+):

public class StringSwitchExample {
    public static void main(String[] args) {
        String color = "green";
        
        switch(color.toLowerCase()) { // Convert to lowercase for case-insensitive comparison
            case "red":
                System.out.println("Red");
                break;
            case "blue":
                System.out.println("Blue");
                break;
            case "green":
                System.out.println("Green");
                break;
            default:
                System.out.println("Unknown color");
        }
    }
}

Result: Green

Example with Enum:

public enum Seasons {
    WINTER,
    SPRING,
    SUMMER,
    AUTUMN
}

public class EnumSwitchExample {
    public static void main(String[] args) {
        Seasons season = Seasons.SUMMER;
        
        switch(season) {
            case WINTER:
                System.out.println("It is winter.");
                break;
            case SPRING:
                System.out.println("It is spring.");
                break;
            case SUMMER:
                System.out.println("It is summer.");
                break;
            case AUTUMN:
                System.out.println("It is autumn.");
                break;
        }
    }
}

Result: It is summer.

Task 1: Age-Based Ticket Price with Ternary Operator

Objective: Create a program to input age and output ticket price. Rewrite the following if-else statement using the ternary conditional operator.

if (ages >= 16) {
    ticketPrice = 20;
} else {
    ticketPrice = 10;
}

Please enter your age
16
Price is 20

[File name and class name: L4Task1.java]

Task 2: Convert Ternary to If-Else

Objective: Create a program that rewrites the following ternary expressions using traditional if-else statements. First declare and initialize all necessary variables with appropriate values.

1. score = (x > 10) ? 3 * scale : 4 * scale;
2. tax = (income > 10000) ? income * 0.2 : income * 0.17 + 1000;
3. System.out.println((number % 3 == 0) ? i : j);

[File name and class name: L4Task2.java]

Lab 1: Coffee Size Selection

Objective: Request user to input a number — coffee size (1=small, 2=medium, 3=large). Output the price (1 — 25 cents, 2 — 50 cents, 3 — 75 cents). Use switch statement. Replace "..." with the code where it's required.

[File name and class name: L4Lab1.java]

Coffee sizes: 1=small, 2=medium, 3=large
Please enter your selection: 
2
The result: Please insert 25 cents
+++
Coffee sizes: 1=small, 2=medium, 3=large
Please enter your selection: 
5
The result: Invalid selection. Please select 1, 2, or 3.

Algorithm:

1. Within the folder 'java' create a new file named L4Lab1.java.
2. In the very first line import the Scanner package:

   
   import ...;

3. Add the class definition and main method:

   
   public class L4Lab1 {
       public static void main(...) {
   
       }
   }

4. Place your cursor immediately after the open curly brace in the main method, then press enter to create a new line.
5. Enter println() method to explain coffee sizes and request user selection:

   
   System.out.println("Coffee sizes: 1=small 2=medium 3=large");

6. Request user to input with println() method:

   
   System.out.println("Please enter your selection:");

7. Create Scanner object:

   
   Scanner scanner = ...;

8. Assign the entered value to a string variable:

   
   String str = ...;

9. Initialize a variable price with value 0:

   
   int price = 0;

10. Create a switch-case statement to test the str variable:

    
    switch (str) {
        case "1":
            price += 25;
            break;
        case "2":
            price += 50;
            break;
        case "3":
            ...;
            ...;
    }

11. Add a default section to output a message for invalid input:

    
    switch (str) {
        case "1":
            price += 25;
            break;
        case "2":
            price += 50;
            break;
        case "3":
            ...;
            ...;
        default:
            System.out.println("Invalid selection. Please select 1, 2, or 3.");
            break;
    }

12. Check the price variable and output the price if valid:

    
    if (price != 0) {
        System.out.printf("Please insert %d cents.%n", price);
    }

13. Press F5 to run the program or use commands for terminal.
14. Experiment with different values to see the output.
15. Save the project and upload the file to the learning management system.

Lab 2: Month to Season Converter

Objective: Create a program that requests a month number from user and displays the corresponding season name. Use switch statement. 

[File name and class name: L4Lab2.java]

Please enter a month number
7
Summer
+++
Please enter a month number
15
Incorrect month number!

Algorithm:

1. Create a new Java file named L4Lab2.java.
2. Import the Scanner class at the top of the file.
3. Define the class L4Lab2 with a main method.
4. Inside the main method, create a Scanner object for user input.
5. Prompt the user to enter a month number (1-12).
6. Read the integer input from the user.
7. Use a switch statement to determine the season based on the month number:
   • ▶ Cases 12, 1, 2: "Winter"
   • ▶ Cases 3, 4, 5: "Spring"
   • ▶ Cases 6, 7, 8: "Summer"
   • ▶ Cases 9, 10, 11: "Autumn"
8. Add a default case to handle invalid month numbers (outside 1-12).
9. Output the corresponding season name or error message.
10. Close the Scanner object.
11. Test the program with different month numbers to ensure correct season output.

Lab 3: Day of Week Message

Objective: Write a program that accepts a string representing a day of the week and outputs a corresponding message (Start of work week, Work day, End of work week soon, Weekend day). Use switch statement. 

[File name and class name: L4Lab3.java]

Enter day of the week (e.g., Monday):
Monday
Start of work week
+++
Enter day of the week (e.g., Monday):
Friday
End of work week soon

Algorithm:

1. Create a new Java file named L4Lab3.java.
2. Import the Scanner class.
3. Define the class L4Lab3 with a main method.
4. Create a Scanner object for user input.
5. Prompt the user to enter a day of the week (e.g., Monday).
6. Read the input string and convert it to lowercase using toLowerCase() for case-insensitive comparison.
7. Use a switch statement to check the input day:
   • ▶ Case "monday": "Start of work week"
   • ▶ Case "friday": "End of work week soon"
   • ▶ Cases "saturday", "sunday": "Weekend day"
   • ▶ Default: "Work day"
8. Output the corresponding message.
9. Close the Scanner object.
10. Test the program with different days of the week to verify correct message output.

Task 3: Importance Level

Objective: Implement a program that accepts a number from 1 to 10 inclusive and returns a word indicating the importance level ("very important" - from 7 to 10, "more important than usual"- from 4 to 6, "normal importance"- from 1 to 3). Use switch statement. 

Input: 5
Output: more important than usual

[File name and class name: L4Task3.java]

Task 4: Traffic Light Colors

Objective: Create a program that requests a color name (red, green, blue). If the color is red, output "Stop!". For green — "Go ahead." For blue — "Attention!". Use switch statement. 

Input: Green
Output: Go ahead.

[File name and class name: L4Task4.java]

Task 5: Day of Week by Number

Objective: Request user to input a serial number of the day of the week (1, 2, 3, …, 7). Check the input and output the name of the day (Monday — 1, Tuesday — 2, etc.). Use switch statement. 

Please enter a number from 1 to 7: 
2
The result: The 2-nd day of the week is Tuesday
+++
Please enter a number from 1 to 7:  
9
The result: There are no such days, please enter 1, 2, ..., 7

[File name and class name: L4Task5.java]