Can you explain what the term 'Stateful' means in the context of software systems?

The term "Stateful" in software systems means that an object or component retains its internal state between calls or interactions. This means that the system's behavior depends not only on the current input but also on previous operations.

For example, in Java, a stateful service can store user data in a session to use this information for subsequent requests. Unlike stateless systems, which do not retain state and handle each request independently.

Example of a stateful object:

public class Counter {
    private int count = 0;

    public int increment() {
        count++;
        return count;
    }
}

Here, the Counter object maintains a state (the value of count), which changes with each call to the increment() method.