Can you explain what a save state operation is?

A stateful operation is an operation or process that preserves and uses internal state between calls or execution steps. In the context of Java, this can mean that an object or method remembers data that affects subsequent calls.

For example, a class that accumulates the sum of numbers passed to it:

public class Accumulator {
    private int sum = 0;

    public void add(int value) {
        sum += value;
    }

    public int getSum() {
        return sum;
    }
}

Here, the Accumulator object maintains state — the current sum — and updates it with each call to add. Unlike stateless operations, which do not depend on previous calls, stateful operations consider and modify internal state.