public void comboChange1(ActionEvent actionEvent) throws IOException {
 
        switch (manufCombobox1.getSelectionModel().getSelectedIndex()){
            case 0:
                Combobox1.getItems().removeAll(Combobox1.getItems());
                BufferedReader br1 = new BufferedReader(new FileReader("000.txt"));
                try {
                    StringBuilder sb1 = new StringBuilder();
                    String line = br1.readLine();
                    while (line != null) {
                        Combobox1.getItems().add(line);
                        sb1.append(line);
                        line = br1.readLine();
                    }
                } finally {
                    br1.close();
                }
                Combobox1.getSelectionModel().select(0);
                break;
            case 1:
                Combobox1.getItems().removeAll(Combobox1.getItems());
                BufferedReader br2 = new BufferedReader(new FileReader("001.txt"));
                try {
                    StringBuilder sb2 = new StringBuilder();
                    String line = br2.readLine();
 
                    while (line != null) {
                        Combobox1.getItems().add(line);
                        sb2.append(line);
                        line = br2.readLine();
                    }
                } finally {
                    br2.close();
                }
                Combobox1.getSelectionModel().select(0);
                break;
            case 2:
                Combobox1.getItems().removeAll(Combobox1.getItems());
                BufferedReader br3 = new BufferedReader(new FileReader("002.txt"));
                try {
                    StringBuilder sb3 = new StringBuilder();
                    String line = br3.readLine();
                    while (line != null) {
                        Combobox1.getItems().add(line);
                        sb3.append(line);
                        line = br3.readLine();
                    }
                } finally {
                    br3.close();
                }
                Combobox1.getSelectionModel().select(0);
                break;
            case 3:
                Combobox1.getItems().removeAll(Combobox1.getItems());
                BufferedReader br4 = new BufferedReader(new FileReader("003.txt"));
                try {
                    StringBuilder sb4 = new StringBuilder();
                    String line = br4.readLine();
                    while (line != null) {
                        Combobox1.getItems().add(line);
                        sb4.append(line);
                        line = br4.readLine();
                    }
                } finally {
                    br4.close();
                }
                Combobox1.getSelectionModel().select(0);
                break;
            case 4:
                Combobox1.getItems().removeAll(Combobox1.getItems());
                BufferedReader br5 = new BufferedReader(new FileReader("004.txt"));
                try {
                    StringBuilder sb5 = new StringBuilder();
                    String line = br5.readLine();
                    while (line != null) {
                        Combobox1.getItems().add(line);
                        sb5.append(line);
                        line = br5.readLine();
                    }
                } finally {
                    br5.close();
                }
                Combobox1.getSelectionModel().select(0);
                break;
        }
    }

public class LoadFile {
    public void comboLoadFile(ComboBox, String filename) throws IOException {
        ComboBox Combobox = new ComboBox();
        Combobox.getItems().removeAll(Combobox.getItems());
        BufferedReader br1 = new BufferedReader(new FileReader(filename));
        try {
            StringBuilder sb1 = new StringBuilder();
            String line = br1.readLine();
            while (line != null) {
                Combobox.getItems().add(line);
                sb1.append(line);
                line = br1.readLine();
            }
        } finally {
            br1.close();
        }
        Combobox.getSelectionModel().select(0);
    }
}

@Override
    public void comboChange1(ActionEvent actionEvent){
        switch (manufCombobox1.getSelectionModel().getSelectedIndex()){
            case 0:
                LoadFile(ComboBox1, "001.txt");
                break;
            case 1:
                LoadFile(ComboBox2, "002.txt");
                break;
            case 2:
                LoadFile(ComboBox3, "003.txt");
                break;
            case 3:
                LoadFile(ComboBox4, "004.txt");
                break;
            case 4:
                LoadFile(ComboBox5, "005.txt");
                break;
        }
    }