JavaFX 监听 文本框输入 限制文本框输入

package fx.com;


import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.image.Image;
import javafx.scene.input.MouseEvent;
import javafx.stage.Stage;

import java.io.IOException;
import java.net.URL;



public class Main extends Application {
    public static void main(String[] args) {
        launch(Main.class, args);
    }

    @Override
    public void start(Stage primaryStage) throws IOException{
        Group group = new Group();
        Scene scene = new Scene(group);
        primaryStage.setScene(scene);
        URL qunlogoUrl = new URL("http://www.haotuo.net.cn/Resources/cq/qunlogo.png");
        primaryStage.setWidth(800);
        primaryStage.setHeight(500);
        primaryStage.getIcons().add(new Image(qunlogoUrl.toExternalForm()));
        primaryStage.setTitle("JavaFX");

        TextField textField = new TextField();
        textField.setStyle(
                "-fx-pref-width: 200;" +
                        "-fx-pref-height: 50;" +
                        "-fx-font-size: 20;"
        );
        textField.setLayoutX(100);
        textField.setLayoutY(100);

        Tooltip tip = new Tooltip("这是提示");
        textField.setTooltip(tip);

        textField.setPromptText("请输入7个文字");
        textField.setFocusTraversable(false);
        //监听文本输入的内容
        textField.textProperty().addListener(new ChangeListener<String>() {
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
                if(newValue.length()>7){
                    System.out.println("超出范围");
                    textField.setText(oldValue);
                }
            }
        });
        //监听文本框里面选择 的内容
        textField.selectedTextProperty().addListener(new ChangeListener<String>() {
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
                System.out.println(newValue);
            }
        });
        PasswordField passwordField = new PasswordField();
        passwordField.setStyle(
                "-fx-pref-width: 200;" +
                        "-fx-pref-height: 50;" +
                        "-fx-font-size: 20;"
        );
        passwordField.setLayoutX(100);
        passwordField.setLayoutY(200);

        Label label = new Label("你在就好了");
        label.setStyle(
                "-fx-pref-width: 200;" +
                        "-fx-pref-height: 50;" +
                        "-fx-font-size: 20;"
        );
        label.setOnMouseClicked(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                System.out.println(13);
            }
        });

        group.getChildren().addAll(textField,passwordField,label);
        primaryStage.show();


    }
}