JavaFX setVisible() not working?

Question

Java

There is a scene with a combobox and a gridpane with buttons. The gridpayne has setVisible(false)

<GridPane fx:id="gridPane" layoutX="14.0" layoutY="53.0" prefHeight="233.0" prefWidth="372.0" visible="false">
      <children>
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="4" GridPane.rowIndex="0" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="5" GridPane.rowIndex="0" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="6" GridPane.rowIndex="0" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="0" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="1" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="2" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="3" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="4" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="5" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="6" GridPane.rowIndex="1" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="0" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="1" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="2" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="3" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="4" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="5" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="6" GridPane.rowIndex="2" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="0" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="1" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="2" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="3" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="4" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="5" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="6" GridPane.rowIndex="3" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="0" GridPane.rowIndex="4" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="1" GridPane.rowIndex="4" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="2" GridPane.rowIndex="4" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="3" GridPane.rowIndex="4" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="4" GridPane.rowIndex="4" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="5" GridPane.rowIndex="4" />
        <Button maxHeight="-1.0" maxWidth="-1.0" minHeight="-1.0" minWidth="-1.0" mnemonicParsing="false" text="Button" GridPane.columnIndex="6" GridPane.rowIndex="4" />
      </children>
      <columnConstraints>
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
      </columnConstraints>
      <rowConstraints>
        <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
        <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
        <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
        <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
        <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
      </rowConstraints>
    </GridPane>

Here is the controller method for the combobox

@FXML
    private void showDays() {
        if(monthCB == null) throw new IllegalStateException("Error");
        monthCB.setOnAction((event)->{
          String month;
            month = monthCB.getItems().toString();
            if(month == "January")
                gridPane.setVisible(true);
        });
    }

It is necessary that when choosing January, a gridpayne would appear.
Maybe I'm doing something wrong, because it seems to me that you can somehow dynamically create all this, and not change the visibility of a pre-created object.
Please tell me what is wrong in the code, and give a couple of tips on how to do it right in general.

Answer 1

month == "January" change to month.equals("January")