Explain the concept of immutability
💡 Concept: Immutability in Java
Immutability refers to objects whose state cannot be changed after creation.
📘 Quick Intro
Immutable objects provide safety from unintended modification and are thread-safe by design.
🧠 Analogy
Think of immutability like a printed book — once printed, its content cannot be changed.
🔧 Technical Explanation
- Immutable objects do not allow modification of fields after construction.
- All fields are final and private, and no setters are provided.
- Common immutable classes: String, wrapper classes (Integer, Boolean).
- Helps in writing thread-safe and predictable code.
- Immutability simplifies debugging and testing.
🎯 Use Cases
- ✅ Use immutable objects for thread safety.
- ✅ Share data safely across threads without synchronization.
- ✅ Use in caching, keys in maps, and constants.
💻 Example: Creating an Immutable Class
public final class ImmutablePerson {
private final String name;
private final int age;
public ImmutablePerson(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() { return name; }
public int getAge() { return age; }
}
❓ Interview Q&A
Q1: What is immutability?
A: Objects whose state cannot be changed after creation.
Q2: Why use immutable objects?
A: Thread safety and simplicity.
Q3: Name some immutable classes in Java.
A: String, wrapper classes.
Q4: How to make a class immutable?
A: Declare final class, private final fields, no setters.
Q5: Are immutable objects thread-safe?
A: Yes, by design.
Q6: Can immutable objects change state?
A: No.
Q7: How does immutability help debugging?
A: Predictable state.
Q8: Can subclasses modify immutable objects?
A: No, final class prevents subclassing.
Q9: What if fields are mutable?
A: Use defensive copying.
Q10: Is immutability related to functional programming?
A: Yes, immutability is a key concept.
📝 MCQs
Q1. What is immutability?
- Objects that can be changed
- Objects that cannot be changed
- Mutable objects
- Static objects
Q2. Why use immutable objects?
- Performance
- Thread safety
- Complexity
- Debugging only
Q3. Name immutable classes in Java
- ArrayList
- HashMap
- String and wrappers
- Scanner
Q4. How to make a class immutable?
- Public class
- Final class with final fields
- Abstract class
- Static class
Q5. Are immutable objects thread-safe?
- No
- Yes
- Sometimes
- Never
Q6. Can immutable objects change?
- Yes
- No
- Sometimes
- Depends
Q7. How immutability helps debugging?
- Random state
- Unpredictable state
- Predictable state
- Complex state
Q8. Can subclasses modify immutable objects?
- Yes
- No
- Sometimes
- Depends
Q9. What if fields are mutable?
- Ignore
- Defensive copy
- Mutable copy
- Delete
Q10. Is immutability related to functional programming?
- No
- Yes
- Maybe
- Unknown
💡 Bonus Insight
Immutability helps write safer, more predictable, and thread-safe Java programs, aligning with modern programming practices.
📄 PDF Download
Need a handy summary for your notes? Download this topic as a PDF!