Why encapsulation matters in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a private field in a class.

C Sharp (C#)

private int [1];

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

Avoid

Bpublic

Cage

Dclass

Attempts:

3 left

💡 Hint

Common Mistakes

Using a keyword like 'public' or 'class' as a field name.

Leaving the field name blank.

The keyword private makes the field accessible only inside the class. Here, age is the field name.

2fill in blank

medium

Complete the code to create a public method that returns the private field value.

C Sharp (C#)

public int GetAge() {
    return [1];
}

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

AGetAge

Bage

Cthis

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the method name instead of the field.

Using 'void' as a return value.

The method returns the private field age. Using age directly returns its value.

3fill in blank

hard

Fix the error in the setter method to correctly assign the value to the private field.

C Sharp (C#)

public void SetAge(int value) {
    [1] = value;
}

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

Athis.value

Bvalue

CSetAge

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning the parameter to itself.

Using 'this.value' which is incorrect here.

The private field age should be assigned the incoming value. Using age = value; correctly updates the field.

4fill in blank

hard

Fill both blanks to create a property that encapsulates the private field.

C Sharp (C#)

public int Age {
    get { return [1]; }
    set { [2] = value; }
}

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

Aage

BAge

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the property name inside getter or setter instead of the field.

Assigning the parameter to itself.

The property Age uses the private field age inside both getter and setter to encapsulate access.

5fill in blank

hard

Fill all three blanks to complete the class with encapsulation for the age field.

C Sharp (C#)

class Person {
    private int [1];

    public int [2] {
        get { return [3]; }
        set { [3] = value; }
    }
}

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

Aage

BAge

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the property name inside its own getter or setter causing infinite recursion.

Not declaring the private field.

The private field age is encapsulated by the public property Age. The property uses the field age in its getter and setter.

Practice

1. What is the main purpose of encapsulation in C#?

easy

A. To allow direct modification of class fields from anywhere

B. To hide the internal data of a class and protect it from outside access

C. To make all class data public for easy access

D. To increase the size of the program

Solution

1. Step 1: Understand encapsulation concept

   Encapsulation means hiding data inside a class to protect it from outside interference.

2. Step 2: Identify the purpose of encapsulation

   It prevents direct access to data, allowing control through methods or properties.

3. Final Answer:

   To hide the internal data of a class and protect it from outside access -> Option B

4. Quick Check:

   Encapsulation = Data protection [OK]

Hint: Encapsulation means hiding data inside classes [OK]

Common Mistakes:

• Thinking encapsulation makes all data public
• Confusing encapsulation with inheritance
• Believing encapsulation increases program size

2. Which of the following is the correct way to declare a private field in a C# class?

easy

A. private int age;

B. public int age;

C. int private age;

D. private: int age;

Solution

1. Step 1: Recall C# syntax for access modifiers

   In C#, the keyword private comes before the type and variable name.

2. Step 2: Check each option

   private int age; uses private int age; which is correct syntax for a private field.

3. Final Answer:

   private int age; -> Option A

4. Quick Check:

   Private field syntax = private int age; [OK]

Hint: Private fields start with 'private' keyword before type [OK]

Common Mistakes:

• Using 'public' instead of 'private' for private fields
• Placing 'private' after the type
• Using C++ style 'private:' which is invalid in C#

3. What will be the output of the following C# code?

class Person {
  private string name = "Alice";
  public string GetName() {
    return name;
  }
}

var p = new Person();
Console.WriteLine(p.GetName());

medium

A. Alice

B. name

C. Compilation error

D. null

Solution

1. Step 1: Understand private field and public method

   The field name is private but accessible inside the class. The method GetName() returns the value of name.

2. Step 2: Check the output of calling GetName()

   Calling p.GetName() returns "Alice", which is printed.

3. Final Answer:

   Alice -> Option A

4. Quick Check:

   Private field accessed via public method = Alice [OK]

Hint: Private data accessed through public method returns actual value [OK]

Common Mistakes:

• Expecting a compilation error due to private field
• Thinking it prints the field name 'name'
• Assuming null because field is private

4. Identify the error in this C# class that tries to encapsulate a field:

class BankAccount {
  private double balance;
  public double GetBalance() {
    return balance;
  }
  public void SetBalance(double amount) {
    balance = amount;
  }
}

var account = new BankAccount();
account.balance = 1000;

medium

A. Method SetBalance should return a value

B. GetBalance method should be private

C. Cannot access private field 'balance' directly outside the class

D. balance should be public to allow direct access

Solution

1. Step 1: Check access to private field outside class

   The code tries to assign account.balance = 1000; but balance is private, so this causes an error.

2. Step 2: Understand encapsulation rules

   Private fields cannot be accessed directly outside the class; access must be through methods like SetBalance.

3. Final Answer:

   Cannot access private field 'balance' directly outside the class -> Option C

4. Quick Check:

   Private fields block direct outside access [OK]

Hint: Private fields can't be accessed directly outside class [OK]

Common Mistakes:

• Thinking private fields can be accessed directly
• Believing setter methods must return values
• Assuming getters should be private

5. You want to protect a class field so it can only be set to positive values. Which encapsulation approach is best in C#?

hard

A. Make the field protected and allow subclasses to set any value

B. Make the field public and check values outside the class

C. Make the field private and provide a public getter only

D. Make the field private and provide a public setter method that validates the value

Solution

1. Step 1: Understand the need for validation

   To ensure only positive values are set, validation must happen inside the class.

2. Step 2: Choose encapsulation method

   Making the field private and using a public setter method with validation allows control over allowed values.

3. Final Answer:

   Make the field private and provide a public setter method that validates the value -> Option D

4. Quick Check:

   Private field + validated setter = safe data [OK]

Hint: Use private field with validated public setter method [OK]

Common Mistakes:

• Making field public and trusting external code
• Providing only a getter without setter
• Using protected without validation