Java Developer interview question · Most asked
Concurrency in Java: synchronized?
Summary
synchronized provides mutual exclusion and memory visibility using an object's monitor lock.
Longer Answer
A synchronized instance method locks this; a synchronized static method locks the Class object; a synchronized block locks the explicit object. Only one thread can hold a given monitor at a time, so protected critical sections execute mutually exclusively.
synchronized also establishes happens-before relationships: exiting a synchronized block flushes changes, and entering a block guarded by the same monitor makes those changes visible. The tradeoff is contention, potential deadlock, and less flexible lock control than java.util.concurrent locks.
Key Points
- A synchronized instance method locks this; a synchronized static method locks the Class object; a synchronized block locks the explicit object
- Only one thread can hold a given monitor at a time, so protected critical sections execute mutually exclusively
- synchronized also establishes happens-before relationships: exiting a synchronized block flushes changes, and entering a block guarded by the same monitor makes those changes visible
- For 'Concurrency in Java: synchronized?', the important signal is that you can explain the concept and also connect it to correctness, performance, and maintainability in production Java code.
A strong answer names the mechanism, describes where mistakes happen, and states the practical rule you would follow when designing or debugging a service
Comparison / Tradeoffs
| Aspect | Notes |
|---|---|
| Core idea | synchronized provides mutual exclusion and memory visibility using an object's monitor lock. |
| Practical tradeoff | The tradeoff is contention, potential deadlock, and less flexible lock control than java.util.concurrent locks. |
Explanation
Summary
synchronized provides mutual exclusion and memory visibility using an object's monitor lock.
Longer Answer
For 'Concurrency in Java: synchronized?', the important signal is that you can explain the concept and also connect it to correctness, performance, and maintainability in production Java code.
A strong answer names the mechanism, describes where mistakes happen, and states the practical rule you would follow when designing or debugging a service.
Key Points
- For 'Concurrency in Java: synchronized?', the important signal is that you can explain the concept and also connect it to correctness, performance, and maintainability in production Java code
- A strong answer names the mechanism, describes where mistakes happen, and states the practical rule you would follow when designing or debugging a service
- Relevant areas: Java, Concurrency
- Use the answer to connect the concept back to a realistic production or interview scenario for 'Concurrency in Java: synchronized?'
Comparison / Tradeoffs
| Aspect | Notes |
|---|---|
| Core idea | synchronized provides mutual exclusion and memory visibility using an object's monitor lock. |
| Practical tradeoff | In an interview, relate 'Concurrency in Java: synchronized?' to implementation decisions, tradeoffs, and operational impact. |