Generic interfaces in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a generic interface named IRepository.

C Sharp (C#)

public interface [1]<T> { void Add(T item); }

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

AIRepository

BICollection

CIList

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name instead of interface name.

Omitting the generic type parameter .

Not starting interface name with 'I'.

The generic interface is named IRepository to follow common C# naming conventions.

2fill in blank

medium

Complete the code to implement the generic interface IRepository for a class named Repository.

C Sharp (C#)

public class Repository<T> : [1]<T> { public void Add(T item) { /* implementation */ } }

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

AIEnumerable

BIRepository

CICollection

DIList

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-generic interface.

Forgetting to specify the generic type parameter .

Using a different interface name.

The class Repository implements the generic interface IRepository with the same type parameter T.

3fill in blank

hard

Fix the error in the interface method declaration to make it generic.

C Sharp (C#)

public interface IRepository<T> { void [1](T item); }

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

AAppend

BInsert

CAddItem

DAdd

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that are not standard or expected.

Using names that do not clearly indicate adding an item.

The method name Add matches the common naming convention for adding an item to a collection.

4fill in blank

hard

Fill both blanks to declare a generic interface with a method that returns an item by index.

C Sharp (C#)

public interface [1]<T> { T [2](int index); }

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

AIRepository

BGetItem

CGet

DIList

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name instead of interface name.

Using a method name that is too long or unclear.

The interface is named IRepository and the method to get an item by index is commonly named Get.

5fill in blank

hard

Fill all three blanks to implement a generic interface with Add and Get methods in a class.

C Sharp (C#)

public class [1]<T> : [2]<T> { private List<T> items = new List<T>(); public void Add(T item) { items.Add(item); } public T [3](int index) { return items[index]; } }

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

ARepository

BIRepository

CGet

DIList

Attempts:

3 left

💡 Hint

Common Mistakes

Using interface name as class name.

Forgetting to implement the interface.

Using incorrect method names.

The class Repository implements the interface IRepository and defines the method Get to retrieve items by index.

Practice

1. What is the main purpose of a generic interface in C#?

easy

A. To allow the interface to work with any data type specified later

B. To restrict the interface to only one specific data type

C. To make the interface private and inaccessible outside its class

D. To automatically implement all methods without code

Solution

1. Step 1: Understand generic interfaces

   Generic interfaces use placeholders (type parameters) to allow flexibility in the data types they work with.

2. Step 2: Identify the purpose

   This flexibility means the same interface can be reused with different types, making code more reusable and type-safe.

3. Final Answer:

   To allow the interface to work with any data type specified later -> Option A

4. Quick Check:

   Generic interface = flexible type [OK]

Hint: Generic interfaces use placeholders for types [OK]

Common Mistakes:

• Thinking generic interfaces fix one type only
• Confusing generic interfaces with access modifiers
• Assuming generic interfaces auto-implement methods

2. Which of the following is the correct syntax to declare a generic interface named IContainer with a type parameter T?

easy

A. interface IContainer<T> () { }

B. interface IContainer { T }

C. interface IContainer<T> { }

D. class IContainer<T> { }

Solution

1. Step 1: Recall generic interface syntax

   Generic interfaces use angle brackets after the interface name to specify type parameters, like IContainer<T>.

2. Step 2: Check each option

   interface IContainer<T> { } correctly declares a generic interface. interface IContainer { T } is invalid syntax. class IContainer<T> { } uses 'class' instead of 'interface'. interface IContainer<T> () { } has incorrect parentheses.

3. Final Answer:

   interface IContainer<T> { } -> Option C

4. Quick Check:

   Generic interface syntax = interface Name<T> [OK]

Hint: Generic interfaces use angle brackets after name [OK]

Common Mistakes:

• Using class instead of interface keyword
• Omitting angle brackets for type parameter
• Adding parentheses after interface name

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

interface IPrinter<T> { void Print(T item); }
class StringPrinter : IPrinter<string> {
  public void Print(string item) { Console.WriteLine(item); }
}
var printer = new StringPrinter();
printer.Print("Hello World");

medium

A. Hello World

B. Compile-time error due to missing type parameter

C. Runtime error due to invalid cast

D. No output

Solution

1. Step 1: Understand interface implementation

   The class StringPrinter implements IPrinter<string> and defines the Print method to write the string to console.

2. Step 2: Trace method call

   The Print method is called with "Hello World", so it prints this string to the console.

3. Final Answer:

   Hello World -> Option A

4. Quick Check:

   Implemented method prints input string [OK]

Hint: Implemented method prints passed argument [OK]

Common Mistakes:

• Expecting compile error for correct generic usage
• Confusing interface with abstract class
• Thinking Print method returns a value

4. Identify the error in this code snippet:

interface IRepository<T> {
  void Add(T item);
}
class Repository : IRepository {
  public void Add(object item) { /* implementation */ }
}

medium

A. Interface IRepository cannot have methods

B. Class Repository must specify the type parameter when implementing IRepository

C. Method Add should return a value

D. Class Repository cannot implement interfaces

Solution

1. Step 1: Check interface implementation

   The interface IRepository is generic and requires a type parameter <T>. The class Repository implements it without specifying this type.

2. Step 2: Identify the fix

   The class must specify the type parameter, for example IRepository<object>, to correctly implement the interface.

3. Final Answer:

   Class Repository must specify the type parameter when implementing IRepository -> Option B

4. Quick Check:

   Generic interface requires type parameter [OK]

Hint: Generic interfaces need type parameters when implemented [OK]

Common Mistakes:

• Omitting type parameter in implementation
• Assuming interface methods must return values
• Thinking classes can't implement interfaces

5. Given the generic interface and classes below, what will be the output?

interface ITransformer<T> {
  T Transform(T input);
}
class IntDoubler : ITransformer<int> {
  public int Transform(int input) => input * 2;
}
class StringRepeater : ITransformer<string> {
  public string Transform(string input) => input + input;
}
var doubler = new IntDoubler();
var repeater = new StringRepeater();
Console.WriteLine(doubler.Transform(5));
Console.WriteLine(repeater.Transform("Hi"));

hard

A. 5
HiHi

B. 55
HiHi

C. 10
Hi

D. 10
HiHi

Solution

1. Step 1: Analyze IntDoubler.Transform

   This method doubles the integer input. For input 5, output is 5 * 2 = 10.

2. Step 2: Analyze StringRepeater.Transform

   This method repeats the string input twice. For input "Hi", output is "Hi" + "Hi" = "HiHi".

3. Final Answer:

   10 HiHi -> Option D

4. Quick Check:

   Int doubled = 10, string repeated = HiHi [OK]

Hint: Trace each Transform method with given input [OK]

Common Mistakes:

• Mixing outputs of different classes
• Forgetting string concatenation doubles text
• Assuming Transform returns original input