Inspecting methods and properties in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of MethodInfo Name Property

What will be the output of this C# code snippet that uses reflection to get method names?

C Sharp (C#)

using System;
using System.Reflection;

class Sample {
    public void Hello() { }
    private int Add(int a, int b) { return a + b; }
}

class Program {
    static void Main() {
        MethodInfo[] methods = typeof(Sample).GetMethods(BindingFlags.Public | BindingFlags.Instance);
        foreach (var method in methods) {
            Console.WriteLine(method.Name);
        }
    }
}

A

Hello
Add

B

Add
Equals
GetHashCode
GetType
ToString

C

Hello
Add
Equals
GetHashCode
GetType
ToString

D

Hello
Equals
GetHashCode
GetType
ToString

💡 Hint

Remember that BindingFlags.Public only includes public methods, so private methods like Add won't appear.

The code uses BindingFlags.Public and Instance to get only public instance methods. 'Hello' is public, 'Add' is private and excluded. The inherited public methods from Object class also appear.

❓ Predict Output

intermediate

PropertyInfo GetValue Output

What will be printed by this C# program that uses reflection to get a property value?

C Sharp (C#)

using System;
using System.Reflection;

class Person {
    public string Name { get; set; } = "Alice";
}

class Program {
    static void Main() {
        Person p = new Person();
        PropertyInfo prop = typeof(Person).GetProperty("Name");
        Console.WriteLine(prop.GetValue(p));
    }
}

A Alice

B Name

C null

D System.String

💡 Hint

GetValue returns the value of the property for the given object instance.

The property 'Name' has the value 'Alice' in the instance p, so GetValue(p) returns 'Alice'.

🔧 Debug

advanced

Why does this reflection code throw an exception?

This code throws a NullReferenceException. What is the cause?

C Sharp (C#)

using System;
using System.Reflection;

class Car {
    private int speed = 100;
}

class Program {
    static void Main() {
        Car c = new Car();
        PropertyInfo prop = typeof(Car).GetProperty("speed");
        Console.WriteLine(prop.GetValue(c));
    }
}

A The class Car does not have any properties, only fields, so GetProperty returns null.

B The field 'speed' is not initialized, causing a null value.

C GetValue requires a static object for private properties.

D The property 'speed' is private and GetProperty without BindingFlags cannot find it, so prop is null.

💡 Hint

Check if 'speed' is a property or a field and how GetProperty works.

GetProperty only finds properties, not fields. 'speed' is a private field, so GetProperty returns null, causing NullReferenceException when calling GetValue.

📝 Syntax

advanced

Which code correctly gets all public properties including inherited ones?

Choose the correct C# code snippet that retrieves all public instance properties of a class including those inherited.

A typeof(MyClass).GetProperties(BindingFlags.NonPublic | BindingFlags.Instance)

B typeof(MyClass).GetProperties(BindingFlags.Public | BindingFlags.Instance)

C typeof(MyClass).GetProperties(BindingFlags.Public | BindingFlags.Static)

D typeof(MyClass).GetProperties(BindingFlags.NonPublic | BindingFlags.Static)

💡 Hint

Public instance properties include those with public getters/setters and are instance members.

BindingFlags.Public | BindingFlags.Instance returns all public instance properties including inherited ones. Other options either get non-public or static properties.

🚀 Application

expert

Count properties with public getter and private setter

Given this class, how many properties have a public getter and a private setter?

C Sharp (C#)

using System;

class Book {
    public string Title { get; private set; }
    public string Author { get; set; }
    public int Pages { get; private set; }
    public DateTime Published { get; private set; }
    private string InternalCode { get; set; }
}

A 1

B 2

C 3

D 4

💡 Hint

Check each property’s getter and setter accessibility carefully.

Title, Pages, and Published have public getters and private setters. Author has public setter, InternalCode is private property.

Practice

1. Which C# method is used to get the type information of an object instance?

easy

A. typeof()

B. GetMethods()

C. GetProperties()

D. GetType()

Solution

1. Step 1: Understand the difference between GetType() and typeof()

   GetType() is called on an object instance to get its runtime type, while typeof() is used with a type name at compile time.

2. Step 2: Identify the method that works on an object instance

   Since the question asks for the method used on an object instance, GetType() is the correct choice.

3. Final Answer:

   GetType() -> Option D

4. Quick Check:

   Object instance method for type info = GetType() [OK]

Hint: Use GetType() on objects, typeof() on type names [OK]

Common Mistakes:

• Confusing typeof() with GetType()
• Using GetMethods() to get type info
• Thinking GetProperties() returns type

2. Which of the following is the correct syntax to get all methods of the String type in C#?

easy

A. typeof(String).GetMethods()

B. typeof(String).GetProperties()

C. String.GetMethods()

D. GetType(String).GetMethods()

Solution

1. Step 1: Recall how to get methods from a type

   Use typeof(TypeName).GetMethods() to get all methods of a type.

2. Step 2: Check each option's syntax

   typeof(String).GetMethods() uses typeof(String).GetMethods(), which is correct. typeof(String).GetProperties() calls GetProperties(), not methods. String.GetMethods() tries to call GetMethods() on the type name directly, which is invalid. GetType(String).GetMethods() uses GetType(String), which is incorrect syntax.

3. Final Answer:

   typeof(String).GetMethods() -> Option A

4. Quick Check:

   Get methods from type = typeof(Type).GetMethods() [OK]

Hint: Use typeof(Type).GetMethods() to list methods [OK]

Common Mistakes:

• Calling GetMethods() on type name directly
• Mixing GetProperties() with GetMethods()
• Using GetType() with a type name instead of instance

3. What will the following C# code output?

var props = typeof(DateTime).GetProperties();
Console.WriteLine(props.Length);

medium

A. 0

B. More than 0

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Understand what GetProperties() returns

   GetProperties() returns an array of all public properties of the type.

2. Step 2: Check if DateTime has properties

   DateTime has many properties like Now, Today, Year, Month, etc., so the array length will be more than zero.

3. Final Answer:

   More than 0 -> Option B

4. Quick Check:

   DateTime properties count > 0 [OK]

Hint: Types like DateTime have many properties, so length > 0 [OK]

Common Mistakes:

• Assuming no properties means length 0
• Expecting compilation or runtime errors
• Confusing methods with properties

4. Identify the error in this C# code snippet:

var typeInfo = "hello".GetType();
var methods = typeInfo.GetMethod();

medium

A. GetType() is invalid on string

B. Missing parentheses on GetType

C. GetMethod() should be GetMethods()

D. Cannot call GetMethod() on typeInfo

Solution

1. Step 1: Check usage of GetType()

   "hello".GetType() is valid and returns the type of the string instance.

2. Step 2: Check method name on typeInfo

   There is no method called GetMethod() without parameters; to get all methods, use GetMethods().

3. Final Answer:

   GetMethod() should be GetMethods() -> Option C

4. Quick Check:

   Use GetMethods() to get all methods [OK]

Hint: Use GetMethods() (plural) to list all methods [OK]

Common Mistakes:

• Using GetMethod() without parameters
• Thinking GetType() is invalid on string
• Missing parentheses on method calls

5. You want to list all public properties of a custom class Person and print their names. Which code snippet correctly does this?

hard

A. var props = typeof(Person).GetProperties(); foreach(var p in props) Console.WriteLine(p.Name);

B. var props = new Person().GetProperties(); foreach(var p in props) Console.WriteLine(p.Name);

C. var props = typeof(Person).GetMethods(); foreach(var p in props) Console.WriteLine(p.Name);

D. var props = Person.GetProperties(); foreach(var p in props) Console.WriteLine(p.Name);

Solution

1. Step 1: Identify how to get properties of a type

   Use typeof(Person).GetProperties() to get all public properties of the Person class.

2. Step 2: Check the foreach loop to print property names

   Iterate over the properties and print each p.Name to display property names.

3. Step 3: Verify other options

   var props = new Person().GetProperties(); foreach(var p in props) Console.WriteLine(p.Name); tries to call GetProperties() on an instance, which is invalid. var props = typeof(Person).GetMethods(); foreach(var p in props) Console.WriteLine(p.Name); gets methods, not properties. var props = Person.GetProperties(); foreach(var p in props) Console.WriteLine(p.Name); calls GetProperties() directly on the class name, which is invalid syntax.

4. Final Answer:

   var props = typeof(Person).GetProperties(); foreach(var p in props) Console.WriteLine(p.Name); -> Option A

5. Quick Check:

   Use typeof(Type).GetProperties() and loop to print names [OK]

Hint: Use typeof(Class).GetProperties() and loop to print names [OK]

Common Mistakes:

• Calling GetProperties() on an instance
• Using GetMethods() instead of GetProperties()
• Calling GetProperties() directly on class name