A Simple Javafx TextField Using TextFormatter To Allow Only Double Value

DoubleFormattedTextFieled.java

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package manager;

import java.util.function.UnaryOperator;
import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.control.TextFormatter;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

/**
 *
 * @author Administrator
 */
public class tata  extends Application{
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        System.out.println("test");
        HBox root = new HBox();

        UnaryOperator<TextFormatter.Change> filter = new UnaryOperator<TextFormatter.Change>() {

            @Override
            public TextFormatter.Change apply(TextFormatter.Change t) {

                if (t.isReplaced()) 
                    if(t.getText().matches("[^0-9]"))
                        t.setText(t.getControlText().substring(t.getRangeStart(), t.getRangeEnd()));
                

                if (t.isAdded()) {
                    if (t.getControlText().contains(".")) {
                        if (t.getText().matches("[^0-9]")) {
                            t.setText("");
                        }
                    } else if (t.getText().matches("[^0-9.]")) {
                        t.setText("");
                    }
                }

                return t;
            }
        };

        TextField tfDouble = new TextField();
        tfDouble.setTextFormatter(new TextFormatter<>(filter));

        root.getChildren().add(tfDouble);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }
}

Regarding line 46:

} else if (t.getText().matches("[^0-9.]")) {

Should one escape the . character so that it matches a literal . character and not use it as it's special meaning? That is:

} else if (t.getText().matches("[^0-9\\.]")) {

You should dynamically get the separator char.

DecimalFormatSymbols decimal = new DecimalFormatSymbols(Locale.getDefault());
String sep = String.valueOf(decimal.getDecimalSeparator());