java_2_8.java

@FXML
void prepareOperation(ActionEvent event) {
    if (event.getSource() == add) {
        this.nextOperation = Operation.ADD;
    } else if (event.getSource() == subtract) {
        this.nextOperation = Operation.SUBTRACT;
    } else if (event.getSource() == multiply) {
        this.nextOperation = Operation.MULTIPLY;
    } else if (event.getSource() == divide) {
        this.nextOperation = Operation.DIVIDE;
    }
    lastResult.setText(input.getText());
    input.setText("");
}