筛选时列表中的Nullpointer异常-Java

Question

嗨，我正在编写代码，用于根据输入内容过滤特定数据。如果输入在数据库中不可用，由于我是Java新手，它会在nullpointer exception上抛出list，我不知道如何解决此错误

private String isCreditRatingValid(String isin) {

        System.out.println(isin);
        List<Credit_rating_details> result = Credit.stream()
                                            .filter(i-> i.getIssuer_id()
                          .contains(isin)).collect(Collectors.toList()); \\throwing NullPointerException on this line\\ 
        if(!result.isEmpty() ) {
            validCreditRating = result.get(0).getCredit_rating();
            return result.get(0).getCredit_rating();
        }else {
            return null;
        }  

Answer 1

根据您的评论，您将其声明为

static ArrayList<Credit_rating_details> Credit = null;

正在对null对象执行操作时导致NPE。将其更改为

static ArrayList<Credit_rating_details> Credit = new ArrayList<Credit_rating_details>();