Difference Between == and Equals() in C#
💡 Concept: == vs Equals() in C#
Both == and Equals() are used to compare objects in C#, but they behave differently based on data type and context.
📘 Quick Intro
The == operator checks for reference equality by default, while Equals() checks for value equality. However, value types override ==, and classes can override Equals().
🧠 Analogy
Imagine two books with identical content. Using == checks if they're the same physical copy (same memory address). Equals() checks if the content of both books is the same, regardless of which copy it is.
🔧 Technical Explanation
==compares references for objects unless overloaded.Equals()compares values/content by default.- For strings, both == and Equals() compare content.
- Structs and primitive types override == to perform value comparison.
- You can override Equals() to customize equality logic.
🎯 Use Cases
- Use == for primitive types and strings when checking value equality.
- Use Equals() when working with overridden equality logic or object types.
- Use ReferenceEquals() to explicitly check object reference identity.
💻 Real Code Example
string a = "hello";
string b = "hello";
Console.WriteLine(a == b); // True
Console.WriteLine(a.Equals(b)); // True
object x = new object();
object y = new object();
Console.WriteLine(x == y); // False
Console.WriteLine(x.Equals(y)); // False
int m = 5, n = 5;
Console.WriteLine(m == n); // True
Console.WriteLine(m.Equals(n)); // True
❓ Interview Q&A
Q1: What is the main difference between == and Equals() in C#?
A: == compares references (for objects) while Equals() compares content.
Q2: How does == behave with strings?
A: It compares the string values, not references.
Q3: What happens if Equals() is not overridden?
A: It uses the default implementation from System.Object, which compares references.
Q4: Can structs override Equals()?
A: Yes, structs can override Equals() to define value-based comparison.
Q5: Is ReferenceEquals() same as ==?
A: No, ReferenceEquals() strictly checks if two references point to the same object.
Q6: How do collections behave with == and Equals()?
A: Collections use Equals() internally for searching and matching elements.
Q7: Can you override == in custom classes?
A: Yes, with operator overloading.
Q8: Should you override Equals() and GetHashCode() together?
A: Yes, to ensure consistent behavior in hash-based collections.
Q9: Which is safer to use in general: == or Equals()?
A: Equals(), especially for objects and custom types.
Q10: Is == a method in C#?
A: No, it is an operator and can be overloaded.
📝 MCQs
Q1. What does == compare for objects by default?
- Values
- HashCode
- References
- Type
Q2. What does Equals() compare in objects?
- References
- Address
- Content or value
- Nullability
Q3. What is the result of 'hello' == 'hello'?
- False
- True
- Error
- Depends
Q4. Which one can be overridden in custom classes?
- ==
- Equals()
- ReferenceEquals()
- All
Q5. Which method checks if two references are the same?
- Equals()
- ==
- Compare()
- ReferenceEquals()
Q6. What does GetHashCode() relate to?
- Sorting
- Type casting
- Overloading
- Hash-based collections
Q7. What is true about == for value types?
- Compares references
- Compares types
- Compares values
- Throws exception
Q8. Which returns true for two identical strings?
- Only Equals()
- Only ==
- Neither
- Both == and Equals()
Q9. What class provides the base Equals() method?
- System.ValueType
- System.String
- System.Base
- System.Object
Q10. Is it necessary to override GetHashCode when Equals() is overridden?
- No
- Only for strings
- Yes
- Depends
💡 Bonus Insight
Understanding == vs Equals() prevents subtle bugs in equality checks—especially when working with custom classes or using collections like Dictionary or HashSet.
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