Panagram JavaFX

Main.java

package sample;

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.scene.text.Font;
import javafx.scene.text.FontWeight;
import javafx.scene.text.Text;
import javafx.stage.Stage;
import javafx.scene.control.Button;

import java.util.HashSet;


public class Main extends Application {

    public boolean isPanagram(String s) {
        HashSet<Integer> h = new HashSet<>();
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) != ' ') {

                int put = (int) s.charAt(i);
                h.add(put);
            }
        }

        if (h.size() == 26) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    public void start(Stage primaryStage) throws Exception{
        GridPane grid = new GridPane();
        grid.setAlignment(Pos.CENTER);
        grid.setHgap(10);
        grid.setVgap(10);
        grid.setPadding(new Insets(25, 25, 25, 25));

        Scene scene = new Scene(grid, 600, 480  );

        Text scenetitle = new Text("Let's check your Panagram!");
        scenetitle.setFont(Font.font("Tahoma", FontWeight.NORMAL, 20));
        grid.add(scenetitle, 0, 0, 2, 1);

        Label panagramLabel = new Label("Panagram:");
        grid.add(panagramLabel, 0, 1);

        TextField userTextField = new TextField();
        grid.add(userTextField, 1, 1);

        Button btn = new Button("Check");
        HBox hbBtn = new HBox(10);
        hbBtn.setAlignment(Pos.BOTTOM_RIGHT);
        hbBtn.getChildren().add(btn);
        grid.add(hbBtn, 1, 4);

        final Text actionTarget = new Text();
        grid.add(actionTarget, 1, 6);

        btn.setOnAction(new EventHandler<ActionEvent>() {

            @Override
            public void handle(ActionEvent e) {
                String panagramString = userTextField.getText();
                if (isPanagram(panagramString)){
                    actionTarget.setFill(Color.FORESTGREEN);
                    actionTarget.setText("This is a panagram.");
                } else {
                    actionTarget.setFill(Color.FIREBRICK);
                    actionTarget.setText("This is not a panagram.");
                }

            }
        });

        primaryStage.setScene(scene);
        primaryStage.setTitle("Panagram checker");

        primaryStage.show();

    }


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