Could you explain the principle of the volatile variable and in what cases its use is justified?

A variable with the volatile modifier in Java (and Android) guarantees that reading and writing to this variable will occur directly from main memory, not from the processor cache. This is important in a multithreaded environment to ensure that changes made by one thread are visible to others.

Without volatile, a thread may see an outdated value of the variable, as it is stored in local cache. With volatile, the following happens:

• Writing to the variable immediately becomes visible to other threads.
• Reading always fetches the current value from memory.

Using volatile is justified when you need to ensure visibility of variable changes between threads without using heavy synchronization, for example, for flags indicating completion or state.

Example:

volatile boolean isRunning = true;

// In one thread
while (isRunning) {
    // work
}

// In another thread
isRunning = false; // will definitely be seen by the first thread

However, volatile does not guarantee atomicity of complex operations (e.g., increment), for which other synchronization mechanisms are needed.