3.6

3.6 Lab - Switch Statements in Java

Introduction

In this lab, you will learn how to use switch statements in Java. The switch statement provides an alternative to the if-else structure when dealing with multiple possible values of a variable. This control structure can make your code more readable when you have a set of predefined values to check. You will write a program that utilizes the switch statement to make decisions based on user input.

Objectives

By the end of this lab, you will be able to:

Understand the structure and syntax of a switch statement in Java.
Use the switch statement to handle multiple cases in a program.
Write a Java program that uses the switch statement to evaluate user input.
Compile and run a Java program using switch statements.

Lab Steps

Step 1: Access the Linux Terminal

Open the terminal on your Linux system.
Ensure you are in your home directory by running the command:
```
cd ~
```

Step 2: Create and Edit a Java File

Create a new Java file using Nano called SwitchExample.java:
```
nano SwitchExample.java
```

Type the following Java code into the file. This program will ask the user for a number between 1 and 7 and then output the corresponding day of the week:

import java.util.Scanner;

public class SwitchExample {
    public static void main(String[] args) {
        // Create a Scanner object for user input
        Scanner scanner = new Scanner(System.in);

        // Prompt the user to enter a number between 1 and 7
        System.out.print("Enter a number (1-7) to select a day of the week: ");
        int day = scanner.nextInt();

        // Switch statement to determine the day of the week
        switch (day) {
            case 1:
                System.out.println("Sunday");
                break;
            case 2:
                System.out.println("Monday");
                break;
            case 3:
                System.out.println("Tuesday");
                break;
            case 4:
                System.out.println("Wednesday");
                break;
            case 5:
                System.out.println("Thursday");
                break;
            case 6:
                System.out.println("Friday");
                break;
            case 7:
                System.out.println("Saturday");
                break;
            default:
                System.out.println("Invalid input! Please enter a number between 1 and 7.");
                break;
        }
    }
}

Save the file by pressing CTRL + O, then hit Enter to confirm the filename.
Exit Nano by pressing CTRL + X.

Step 3: Compile the Java Program

In the terminal, compile the Java program using the javac command:
```
javac SwitchExample.java
```
If there are no errors, this command will create a file named SwitchExample.class. Verify this by running:
```
ls
```

Step 4: Run the Java Program

Run the compiled program using the java command:
```
java SwitchExample
```
The program will prompt you to enter a number between 1 and 7. Based on the number you enter, the program will output the corresponding day of the week. For example:
```
Enter a number (1-7) to select a day of the week: 3
Tuesday
```

Step 5: Modify the Program

Open the SwitchExample.java file again using Nano:
```
nano SwitchExample.java
```

Modify the program to ask the user to choose a number between 1 and 12 and display the corresponding month of the year using a switch statement:

System.out.print("Enter a number (1-12) to select a month of the year: ");
int month = scanner.nextInt();

switch (month) {
    case 1:
        System.out.println("January");
        break;
    case 2:
        System.out.println("February");
        break;
    case 3:
        System.out.println("March");
        break;
    case 4:
        System.out.println("April");
        break;
    case 5:
        System.out.println("May");
        break;
    case 6:
        System.out.println("June");
        break;
    case 7:
        System.out.println("July");
        break;
    case 8:
        System.out.println("August");
        break;
    case 9:
        System.out.println("September");
        break;
    case 10:
        System.out.println("October");
        break;
    case 11:
        System.out.println("November");
        break;
    case 12:
        System.out.println("December");
        break;
    default:
        System.out.println("Invalid input! Please enter a number between 1 and 12.");
        break;
}

Save, exit, recompile, and run the program again to see the updated behavior:
```
javac SwitchExample.java
java SwitchExample
```

Step 6: Add More Functionality

Modify the program to include both options (day of the week and month of the year). Use a switch statement to prompt the user to first choose between the two categories, and then proceed to either the day or month selection:

System.out.print("Enter 1 for day selection, 2 for month selection: ");
int choice = scanner.nextInt();

switch (choice) {
    case 1:
        // Ask for day
        System.out.print("Enter a number (1-7) to select a day of the week: ");
        int day = scanner.nextInt();

        switch (day) {
            case 1:
                System.out.println("Sunday");
                break;
            case 2:
                System.out.println("Monday");
                break;
            case 3:
                System.out.println("Tuesday");
                break;
            case 4:
                System.out.println("Wednesday");
                break;
            case 5:
                System.out.println("Thursday");
                break;
            case 6:
                System.out.println("Friday");
                break;
            case 7:
                System.out.println("Saturday");
                break;
            default:
                System.out.println("Invalid input! Please enter a number between 1 and 7.");
                break;
        }
        break;
    case 2:
        // Ask for month
        System.out.print("Enter a number (1-12) to select a month of the year: ");
        int month = scanner.nextInt();

        switch (month) {
            case 1:
                System.out.println("January");
                break;
            case 2:
                System.out.println("February");
                break;
            case 3:
                System.out.println("March");
                break;
            case 4:
                System.out.println("April");
                break;
            case 5:
                System.out.println("May");
                break;
            case 6:
                System.out.println("June");
                break;
            case 7:
                System.out.println("July");
                break;
            case 8:
                System.out.println("August");
                break;
            case 9:
                System.out.println("September");
                break;
            case 10:
                System.out.println("October");
                break;
            case 11:
                System.out.println("November");
                break;
            case 12:
                System.out.println("December");
                break;
            default:
                System.out.println("Invalid input! Please enter a number between 1 and 12.");
                break;
        }
        break;
    default:
        System.out.println("Invalid input! Please choose 1 or 2.");
        break;
}

Save, exit, recompile, and run the program to test the updated functionality.

Step 7: Cleanup (Optional)

Once you're done, clean up the directory by removing the .class files:
```
rm *.class
```

Summary

In this lab, you learned how to use the switch statement to handle multiple conditions in Java. You explored how switch is used as an alternative to if-else for checking multiple values. You implemented a program that allowed users to choose a day of the week or a month of the year, and expanded it to include more user input options. The switch statement is a powerful tool for simplifying decision-making logic when you have multiple discrete values to evaluate.