Calculator with lambdas

package calcwithlambda;

/**
 *
 * @author Aamir khan
 */
import java.util.Arrays;
import java.util.function.BinaryOperator;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

public class Calculator extends Application {

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

    @Override
    public void start(Stage stage) {
        stage.setTitle("A Simple Calculator");

        ComboBox<Operation> operations = new ComboBox<>();
        operations.getItems().addAll(Arrays.asList(Operation.values()));
        operations.setValue(Operation.values()[0]);

        TextField[] input = new TextField[2];
        for (int i = 0; i < input.length; i++) {
            input[i] = new TextField();
            input[i].setPromptText("Enter a number");
        }

        Label result = new Label("Click calculate for result");

        Button calculate = new Button("Calculate");
        calculate.setOnAction(
                e -> result.setText(
                        computeResult(
                                (Operation) operations.getValue(),
                                input[0].getText(),
                                input[1].getText()
                        )
                )
        );

        HBox box = new HBox();
        box.getChildren().addAll(
                input[0], operations, input[1], calculate, result
        );

        Group root = new Group();
        root.getChildren().add(box);

        final Scene scene = new Scene(root);
        //apply your css for the styling
        scene.getStylesheets().add("http://pastebin.com/raw.php?i=wxn9WiVf");
        scene.setFill(Color.WHITE);

        stage.initStyle(StageStyle.UTILITY);
        stage.setScene(scene);
        stage.sizeToScene();
        stage.centerOnScreen();
        stage.show();
    }

    private  String computeResult(Operation op, String val1, String val2) {
        double result = op.apply(
                Double.parseDouble(val1),
                Double.parseDouble(val2)
        );

        return result == (int) result
                ? String.valueOf((int) result)
                : String.format("%.2f", result);
    }

    enum Operation implements BinaryOperator<Double>{

        ADD((x, y) -> x + y),
        SUBTRACT((x, y) -> x - y),
        MULTIPLY((x, y) -> x * y),
        DIVIDE((x, y) -> x / y),
        MOD((x, y) -> x % y),
        HYPOTENUSE(Math::hypot),
        EXPONENTIATE(Math::pow);

        private final BinaryOperator<Double> equation;

        Operation(BinaryOperator<Double> equation) {
            this.equation = equation;
        }

//        public Equation getEquation() {
//            return this.equation;
//        }

        @Override
        public String toString() {
            return this.name().charAt(0) + this.name().substring(1).toLowerCase();
        }

        @Override
        public Double apply(Double t, Double u) {
            return equation.apply(t, u);
        }
    }
}