Use cases in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple class named User.

Java

public class [1] {
    // class body
}

Drag options to blanks, or click blank then click option'

Auser

BUser

CMain

DAccount

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase for class names

Using unrelated class names

The class name should start with an uppercase letter and match the intended name. Here, User is the correct class name.

2fill in blank

medium

Complete the code to create a method named greet that returns a String.

Java

public class Greeter {
    public [1] greet() {
        return "Hello!";
    }
}

Drag options to blanks, or click blank then click option'

AString

Bint

Cvoid

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using void which means no return value

Using numeric or boolean types incorrectly

The method returns a text message, so its return type must be String.

3fill in blank

hard

Fix the error in the code to correctly instantiate an object of class Car.

Java

public class Car {
    String model;

    public Car(String model) {
        this.model = model;
    }
}

Car myCar = new [1]("Tesla");

Drag options to blanks, or click blank then click option'

ACar

Bcar()

Ccar

DVehicle

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase class name

Using a different class name

Adding parentheses after class name in the wrong way

Class names are case-sensitive and must match exactly. The correct class name is Car with uppercase C.

4fill in blank

hard

Fill both blanks to create a method that checks if a user is adult based on age.

Java

public class User {
    int age;

    public boolean isAdult() {
        return age [1] [2];
    }
}

Drag options to blanks, or click blank then click option'

A>=

B18

C<

D21

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator instead of greater or equal

Using wrong age number like 21

The method returns true if age is greater than or equal to 18, which means the user is an adult.

5fill in blank

hard

Fill all three blanks to create a method that returns a map of user names and their ages if age is above 20.

Java

import java.util.Map;
import java.util.HashMap;

public class UserData {
    Map<String, Integer> users = new HashMap<>();

    public Map<String, Integer> getAdults() {
        Map<String, Integer> adults = new HashMap<>();
        for (String [1] : users.keySet()) {
            int [2] = users.get([1]);
            if ([2] [3] 20) {
                adults.put([1], [2]);
            }
        }
        return adults;
    }
}

Drag options to blanks, or click blank then click option'

Aname

Bage

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names

Using less than operator instead of greater than

The loop variable is name, the age is retrieved into age, and the condition checks if age is greater than 20.

Practice

1. What is the main purpose of a use case in Java programming?

easy

A. To debug syntax errors

B. To write the actual Java code

C. To compile the Java program

D. To describe how users interact with the program

Solution

1. Step 1: Understand the definition of use case

   A use case explains how users will use or interact with a program, focusing on user actions and system responses.

2. Step 2: Differentiate use case from coding tasks

   Writing code, compiling, or debugging are programming tasks, not the purpose of use cases.

3. Final Answer:

   To describe how users interact with the program -> Option D

4. Quick Check:

   Use case = user interaction description [OK]

Hint: Use cases focus on user actions, not code details [OK]

Common Mistakes:

• Confusing use cases with code writing
• Thinking use cases are for debugging
• Assuming use cases are about compiling

2. Which of the following is the correct way to write a simple use case step in Java documentation?

easy

A. if(user == null) { throw new Exception(); }

B. User clicks the 'Login' button to access the system.

C. System.out.println('Login successful');

D. int loginButton = 1;

Solution

1. Step 1: Identify use case style

   Use cases are written as simple, clear steps describing user actions, not code.

2. Step 2: Check options for descriptive text

   User clicks the 'Login' button to access the system. describes a user action clearly; others are code snippets, not use case steps.

3. Final Answer:

   User clicks the 'Login' button to access the system. -> Option B

4. Quick Check:

   Use case step = user action description [OK]

Hint: Use case steps are plain user actions, not code [OK]

Common Mistakes:

• Writing code instead of user actions
• Using technical syntax in use case steps
• Mixing code and use case descriptions

3. Given this use case description:

1. User enters username and password.
2. System validates credentials.
3. System grants access if valid.
4. System shows error if invalid.

What is the expected system behavior if the user enters wrong password?

medium

A. System shows error

B. System grants access

C. System crashes

D. System ignores input

Solution

1. Step 1: Analyze the use case steps

   Step 4 says system shows error if credentials are invalid.

2. Step 2: Apply to wrong password case

   Wrong password means invalid credentials, so system shows error.

3. Final Answer:

   System shows error -> Option A

4. Quick Check:

   Invalid credentials = show error [OK]

Hint: Invalid login means error message shown [OK]

Common Mistakes:

• Choosing system grants access for wrong password
• Assuming system crashes on error
• Ignoring error handling step

4. Identify the error in this use case step:

Step 2: System checks if user password is correct.
Step 3: If password is wrong, system grants access.

medium

A. Step 3 should deny access if password is wrong

B. Step 2 should accept any password

C. Step 3 should crash the system

D. No error, steps are correct

Solution

1. Step 1: Review step 3 logic

   Granting access on wrong password is a security error.

2. Step 2: Correct expected behavior

   System should deny access or show error if password is wrong.

3. Final Answer:

   Step 3 should deny access if password is wrong -> Option A

4. Quick Check:

   Wrong password = deny access [OK]

Hint: Wrong password must never grant access [OK]

Common Mistakes:

• Allowing access on wrong password
• Ignoring security in use case steps
• Assuming system crashes on wrong input

5. You want to write a use case for a Java program that allows users to reset their password. Which sequence of steps best fits this use case?

hard

A. User logs in -> System checks password -> System grants access -> User resets password

B. System resets password automatically -> User notified -> User logs in

C. User requests password reset -> System sends reset link -> User sets new password -> System confirms update

D. User changes username -> System updates profile -> User logs out

Solution

1. Step 1: Identify correct password reset flow

   Reset involves user request, system sending link, user setting new password, and confirmation.

2. Step 2: Compare options to expected flow

   User requests password reset -> System sends reset link -> User sets new password -> System confirms update matches this flow clearly; others describe unrelated or incorrect sequences.

3. Final Answer:

   User requests password reset -> System sends reset link -> User sets new password -> System confirms update -> Option C

4. Quick Check:

   Password reset = request, link, new password, confirm [OK]

Hint: Password reset needs user action and confirmation steps [OK]

Common Mistakes:

• Confusing login with password reset
• Assuming system resets password without user input
• Mixing username change with password reset