Module: | Arrays, Strings & Exception Handling
Q55: Consider the following statements regarding the volatile keyword in Java multithreading:
1. Declaring a variable with the volatile keyword guarantees that all reads and writes to that variable are executed directly against the main RAM memory, entirely bypassing local CPU caches.
2. The volatile keyword inherently provides absolute thread-safety and atomicity for compound operations, meaning a volatile counter can be safely incremented using the count++ syntax.
3. The Java compiler strictly prohibits applying the volatile keyword to classes, methods, or local variables; it is exclusively reserved for instance or static fields.
Which of the above statements is/are correct?
2. The volatile keyword inherently provides absolute thread-safety and atomicity for compound operations, meaning a volatile counter can be safely incremented using the count++ syntax.
3. The Java compiler strictly prohibits applying the volatile keyword to classes, methods, or local variables; it is exclusively reserved for instance or static fields.
Which of the above statements is/are correct?
✅ Correct Answer: B
🎯 Quick Answer:
The correct combination is 1 and 3. Statement 2 is incorrect because the volatile keyword absolutely does not guarantee atomicity. The increment operator (count++) is actually three separate steps (read, add, write). Even with volatile, two threads can read the same volatile value simultaneously, increment it, and overwrite each other, causing data loss.Structural Breakdown: In modern multi-core processors, each core has its own ultra-fast L1/L2 cache.
By default, threads copy variables from main memory into their core's local cache.
If Thread A updates a standard variable, Thread B might never see the update because it is reading from its own isolated cache.
Volatile forces all interactions back to the shared main memory.
Historical/Related Context: Before the java.util.concurrent.atomic package was introduced in Java 5, developers frequently misused volatile, falsely believing it provided total synchronization.
Today, if true atomic compound operations are required without heavy locks, developers must strictly utilize classes like AtomicInteger instead of volatile primitives.
Causal Reasoning: Volatile cannot be applied to local variables (Statement 3 context) because local variables are stored entirely within the Thread's isolated Stack memory.
Because a local variable is physically inaccessible to any other thread in the application, applying a visibility keyword to it is a mathematical and architectural contradiction.