package testbean;

import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

public class SomeFxBean {

    //<editor-fold defaultstate="collapsed" desc="titleProperty">
    private final StringProperty title = new SimpleStringProperty();

    public String getTitle() {
        return title.get();
    }

    public void setTitle(String value) {
        title.set(value);
    }

    public StringProperty titleProperty() {
        return title;
    }
    //</editor-fold>

    public final IntegerProperty anotherProperty = new SimpleIntegerProperty();

}

package testbean;

import java.util.function.Function;
import javafx.util.StringConverter;

import static java.lang.System.out;

public class TestBean {

    public static void main(String[] args) {
        SomeFxBean bean = new SomeFxBean();

        bean.titleProperty().bindBidirectional(bean.anotherProperty, stringConverter(
                text -> text.length(),
                number -> {
                    int size = number.intValue();
                    StringBuilder sb = new StringBuilder(size);
                    for (int i = 0; i < size; ++i) {
                        sb.append('*');
                    }
                    return sb.toString();
                }
        ));

        bean.titleProperty().addListener((all, was, become)
                -> out.println(
                        "titleProperty:" + "\n" +
                        "  old value: " + was + "\n" +
                        "  new value: " + become + "\n"
                )
        );

        bean.anotherProperty.addListener((all, was, become)
                -> out.println(
                        "----------" + "\n" +
                        "anotherProperty:" + "\n" +
                        "  old value: " + was + "\n" +
                        "  new value: " + become + "\n" +
                        "----------" + "\n"
                )
        );

        bean.setTitle("1");
        bean.setTitle("2");
        bean.setTitle("3");
        bean.setTitle("100");

        bean.anotherProperty.set(30);
        bean.titleProperty().set("Так тоже можно");

    }

    public static <T> StringConverter<T> stringConverter(
            Function<String, T> from,
            Function<T, String> to
    ) {
        return new StringConverter<T>() {
            @Override public String toString(T object) {
                return to.apply(object);
            }

            @Override public T fromString(String string) {
                return from.apply(string);
            }
        };
    }
}