Can System.out.println() Output Be Interleaved in Multithreaded Java?

Interleaving in Multi-threaded Output from System.out.println

In a multi-threaded environment, the question arises whether output from the System.out.println(String) method can be interleaved when multiple threads make concurrent calls.

The Java API documentation provides no explicit information on thread safety for System.out or the println method. Therefore, we cannot assume it as such.

It is conceivable that JVM implementations might utilize thread-safe functions for println, leading to non-interleaved output. However, this behavior is not guaranteed across different JVM implementations.

To ensure non-interleaving of output, manual enforcement of mutual exclusion is necessary:

public synchronized void safePrintln(String s) {
    System.out.println(s);
}

Note that this method alone is insufficient as all code must use it and avoid direct calls to System.out.println(String).

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