JavaFX - 自动增量 ID

Question

This is what I have

public class AddNewCategoryController implements Initializable {

    @FXML
    private TextField name;

    @FXML
    private TextField description;

    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
    }

    public void save(){
        final AtomicLong identifier = new AtomicLong(5);
        Long id = identifier.incrementAndGet();
        String catgoryName = name.getText();
        String categoryDescription = description.getText();

        Category category = new Category(id,catgoryName,categoryDescription);

        ReadingDataFromFiles.writeCategory(category);

    }
}

When the programs runs there's a screen to add a new category and the user has to write category's name and description but ID should be automatic and should be increased every time the user enters a new Category. The way I've done it doesn't work as intended, it's increased only once but since initial value stays 5 it's always 6.

Answer 1

Move this line:

final AtomicLong identifier = new AtomicLong(5);

… higher up, outside the method, to be a member field on the class.

In your existing code, each call to that save method is creating a new AtomicLong to replace the previous one. So your counting cannot accumulate.

Proper naming can help clarify. That AtomicLong is not an “identifier”. It is an “identifierGenerator”. Each number returned by its incrementAndGet method is the “identifier”.