In Java, both volatile and static are keywords that apply to variables, but they serve very different purposes and have different behaviors.
Volatile Variables
The volatile keyword in Java is used to mark a variable as "stored in main memory." Essentially, it means that every read of a volatile variable will be read from the main memory, and not from the CPU cache, and every write to a volatile variable will be written to main memory, and not just to the CPU cache[3][5][7][10].
Key Characteristics of Volatile Variables:
Visibility: It ensures that changes made to a volatile variable by one thread are immediately visible to other threads[1][3][5].
No Caching: Threads cannot cache volatile variables; they must read from and write to the main memory[2][3][5].
No Atomicity Guarantee: Volatile does not guarantee atomicity for compound operations (like incrementing a value)[1][5].
Ordering: It prevents instruction reordering which could otherwise optimize code execution but would not be safe in a multithreading context[3][7].
Static Variables
The static keyword, on the other hand, is used to indicate that a particular field or method belongs to the class, rather than instances of the class[4][6][11][12].
Key Characteristics of Static Variables:
Class Level: Static variables are class-level variables, meaning they are shared among all instances of the class[2][4][6].
Single Copy: There is only one copy of a static variable in memory, regardless of how many objects of the class exist[4][6][11].
Memory Efficiency: They are memory efficient as they are not duplicated for each instance[6][12].
Initialization: Static variables are initialized when the class is loaded by the JVM[11][12].
Comparison
Scope and Lifetime: Volatile variables have the same scope as normal instance variables but are always read from and written to main memory. Static variables have a broader scope (class level) and live as long as the class stays loaded in the JVM.
Thread Safety: Volatile variables contribute to thread safety by ensuring visibility of changes across threads. Static variables can be shared across threads but do not inherently provide any thread safety mechanisms[5][6].
Usage Context: Volatile is typically used for variables that are accessed by multiple threads without r...
