Difference between == and equals() method
💡 Concept: == Operator vs equals() Method
The == operator checks reference equality, while the equals() method checks logical equality of objects in Java.
📘 Quick Intro
== compares memory addresses; equals() compares object content. By default, equals() behaves like == unless overridden.
🧠 Analogy
Think of == as checking if two people live in the same house (same address), whereas equals() checks if two people have the same characteristics.
🔧 Technical Explanation
- == compares references (memory addresses).
- equals() compares object data, usually overridden for logical comparison.
- For primitives, == compares values directly.
- Strings override equals() to compare character sequences.
- Custom classes should override equals() for proper logical equality.
🎯 Use Cases
- ✅ Use == to check if two references point to the same object.
- ✅ Use equals() to check if two objects are logically equal.
- ✅ Override equals() in custom classes to define logical equality.
💻 Example: Using == vs equals()
String a = new String("test");
String b = new String("test");
System.out.println(a == b); // false, different objects
System.out.println(a.equals(b)); // true, same content
❓ Interview Q&A
Q1: What does == operator compare?
A: Reference equality (memory address).
Q2: What does equals() method compare?
A: Logical equality of object content.
Q3: Can equals() be overridden?
A: Yes, to define custom equality.
Q4: How do Strings compare with ==?
A: Checks if same object reference.
Q5: How do Strings compare with equals()?
A: Checks if character sequences are equal.
Q6: Is == suitable for primitives?
A: Yes, compares values directly.
Q7: What is the default equals() behavior?
A: Same as == unless overridden.
Q8: Can == be used to compare different object types?
A: Yes, but usually false.
Q9: Why override equals()?
A: To compare logical equality, not references.
Q10: What else should be overridden with equals()?
A: hashCode() method.
📝 MCQs
Q1. What does == compare?
- Value equality
- Reference equality
- Type equality
- Hash equality
Q2. What does equals() compare?
- Reference equality
- Logical equality
- Memory address
- Object type
Q3. Can equals() be overridden?
- No
- Yes
- Sometimes
- Never
Q4. How do Strings compare with ==?
- Checks reference
- Checks content
- Checks hash
- Throws error
Q5. How do Strings compare with equals()?
- Checks content
- Checks reference
- Checks type
- Throws error
Q6. Is == suitable for primitives?
- No
- Yes
- Sometimes
- Never
Q7. What is default equals() behavior?
- Overrides reference
- Same as ==
- Throws error
- Depends on JVM
Q8. Can == compare different object types?
- No
- Yes
- Sometimes
- Never
Q9. Why override equals()?
- Reference equality
- Logical equality
- Performance
- Memory
Q10. What else to override with equals()?
- toString()
- hashCode()
- compareTo()
- finalize()
💡 Bonus Insight
Understanding == vs equals() is critical for Java developers to avoid bugs in object comparisons and collections usage.
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