When is it Necessary to Call `System.exit` in Java?

When is it Necessary to Call System.exit in Java?

In the provided code snippet:

public class TestExit {
    public static void main(String[] args) {
        System.out.println("hello world");

        System.exit(0); // is it necessary? And when it must be called?
    }
}

the System.exit method is used to explicitly terminate the Java program.

Purpose of System.exit

The primary purpose of System.exit is to trigger a controlled shutdown of the Java Virtual Machine (JVM). Calling System.exit does the following:

• Terminates all non-daemon threads.
• Triggers the execution of registered shutdown hooks.
• Releases resources held by the JVM, such as file handles and network connections.

When to Call System.exit

In general, it is not necessary to call System.exit in Java programs. The JVM will automatically terminate when the main method returns or when all non-daemon threads have finished executing.

However, there are certain scenarios where calling System.exit is useful or even necessary:

• Inducing an immediate shutdown: When you want to terminate the program abruptly, regardless of the status of non-daemon threads.
• Using shutdown hooks: When you need to register shutdown hooks to perform specific cleanup tasks before the program exits. These hooks are triggered by System.exit.

Meaning of "This method never returns normally."

The documentation states that System.exit "This method never returns normally." This means that once the method is called, the thread that called it cannot continue its execution and always exits the JVM.

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