unfinished Javafx lab 9

import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;
import javafx.util.Duration;

public class Microwave extends Application {
    static Timeline timeline;

    static int time;

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

    @Override
    public void start(Stage stage) throws Exception {
        // creating label
        Label label = new Label("Place Food Here");
        AnchorPane anchor_pane = new AnchorPane(label);
        AnchorPane.setTopAnchor(label, 70.0);

        // creating textfield
        TextField text_field = new TextField("Time to be displayed here");
        text_field.setMinWidth(250.0);
        AnchorPane.setLeftAnchor(text_field, 85.0);
        anchor_pane.getChildren().add(text_field);

        // creating buttons on gridpane
        GridPane grid_pane = new GridPane();

        // Add buttons to the panel
        int count = 1;
        for (int row = 0; row < 3; row++) {
            for (int col = 0; col < 3; col++) {
                Button btn = buttonContent(String.valueOf(count));
                btn.setOnMouseClicked(e -> {
                    checkTextField(text_field);
                    text_field.setText(text_field.getText() + btn.getText());
                });
                grid_pane.add(btn, col, row);
                count++;
            }
        }
        // 0 button
        Button btn0 = buttonContent(String.valueOf(0));
        btn0.setOnMouseClicked(e -> {
            checkTextField(text_field);
            text_field.setText(text_field.getText() + btn0.getText());
        });
        grid_pane.add(btn0, 0, 3);

        // start button
        Button start_btn = buttonContent("Start");
        start_btn.setOnMouseClicked(e -> {
            startTimer(text_field);
        });
        grid_pane.add(start_btn, 1, 3);

        // stop button
        Button stop_btn = buttonContent("Stop");
        stop_btn.setOnMouseClicked(e -> {
            stopTimer();
        });
        grid_pane.add(stop_btn, 2, 3);

        grid_pane.setStyle("-fx-border-color:rgba(255,0,0,1);");
        grid_pane.setHgap(4);
        grid_pane.setVgap(4);
        grid_pane.setPadding(new Insets(10, 9, 10, 13));
        AnchorPane.setTopAnchor(grid_pane, 25.0);
        AnchorPane.setLeftAnchor(grid_pane, 85.0);
        anchor_pane.getChildren().add(grid_pane);

        Scene scene = new Scene(anchor_pane, 318, 159);
        stage.setTitle("Microwave Oven");
        stage.setScene(scene);
        stage.show();
    }

    private static Button buttonContent(String text) {
        Button b = new Button(text);
        b.setMinWidth(67);

        return b;
    }

    private static void checkTextField(TextField tx) {
        if (tx.getText().equals("Time to be displayed here")) {
            tx.setText("");
        }
    }

    private static void startTimer(TextField tx) {
        time = Integer.parseInt(tx.getText());
        KeyFrame kf = new KeyFrame(Duration.millis(1000), e -> {
            time--;
            if (time == 0) {
                timeline.stop();
            }
            tx.setText(Integer.toString(time));
        });

        timeline = new Timeline(kf);
        timeline.setCycleCount(Timeline.INDEFINITE);
        timeline.play();
    }

    private static void stopTimer() {
        timeline.pause();
    }
}