JavaFX TextField validation for integer input and also allow either K or k(for Thousand) or M or m(for Million) in last

Question

I want to add validation in javafx TextField such that user should only be able to insert integer values ([0-9] and Dot ). Also user should be able to insert either B or b(for B

Answer 1

As well as listening to changes in the text property and reverting if they are invalid, you can use a TextFormatter to veto changes to the text. Using this approach will avoid other listeners to the textProperty seeing the invalid value and then seeing it revert to the previous value: i.e. the textProperty will always contain something valid.

The TextFormatter takes a UnaryOperator which acts as a filter. The filter can return null to veto the change entirely, or can modify properties of the Change as needed.

Here is a fairly straightforward example, where "k" or "K" is replaced by "000", "m" or "M" by "000000", and other non-digit characters are removed:

import java.util.function.UnaryOperator;

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.control.TextFormatter;
import javafx.scene.control.TextFormatter.Change;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class TextFieldFilteringExample extends Application {

    @Override
    public void start(Stage primaryStage) {
        TextField textField = new TextField();

        textField.textProperty().addListener((obs, oldValue, newValue) -> {
           System.out.println("Text change from "+oldValue+" to "+newValue);
        });

        UnaryOperator filter = change -> {
            if (change.isAdded()) {
                String addedText = change.getText();
                if (addedText.matches("[0-9]*")) {
                    return change ;
                }
                // remove illegal characters:
                int length = addedText.length();
                addedText = addedText.replaceAll("[^0-9kKmM]", "");
                // replace "k" and "K" with "000":
                addedText = addedText.replaceAll("[kK]", "000");
                // replace "m" and "M" with "000000":
                addedText = addedText.replaceAll("[mM]", "000000");
                change.setText(addedText);

                // modify caret position if size of text changed:
                int delta = addedText.length() - length ;
                change.setCaretPosition(change.getCaretPosition() + delta);  
                change.setAnchor(change.getAnchor() + delta);
            }
            return change ;
        };

        textField.setTextFormatter(new TextFormatter(filter));

        StackPane root = new StackPane(textField);
        root.setPadding(new Insets(20));
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

You could also modify the text to introduce grouping separators (e.g. 1,000,000), though the logic gets quite tricky there. You can additionally specify a StringConverter for the text formatter, so that the formatter itself has a value of type BigInteger which is the result of passing the text through the supplied converter.