java.lang.nullpointerexception：使用try/catch创建列表时格式化
我有一个客户介绍类：
public class CustomerRepository {
private static final String FILE_PATH = "src/poly/customer/data.txt";
public List<AbstractCustomer> customers;
{
try {
customers = readFiles();
} catch (IOException e) {
e.printStackTrace();
}
}
private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy");
public List<AbstractCustomer> readFiles() throws IOException{
List<AbstractCustomer> result = new ArrayList<>();
List<String> lines = Files.readAllLines(Path.of(FILE_PATH));
for (String line : lines) {
String[] parts = line.split(";");
int points = Integer.parseInt(parts[3]);
LocalDate date = LocalDate.parse(parts[4], formatter);
if (parts[0].equals("REGULAR")) {
RegularCustomer customer = new RegularCustomer(parts[1], parts[2], points, date);
result.add(customer);
} else if (parts[0].equals("GOLD")) {
GoldCustomer customer = new GoldCustomer(parts[1], parts[2], points);
result.add(customer);
} else {
throw new IOException();
}
}
return result;
}
我想从文件中阅读客户，然后将其添加到客户列表中。我试图这样做：
{
try {
customers = readFiles();
} catch (IOException e) {
e.printStackTrace();
}
}
这给了我java.lang.nullpointerexception：formatter，我该如何修复？此方法应从文本文件中创建对象，然后将它们添加到客户列表中。我的文本文件看起来像这样：
常规; C1; Alice; 0; 2022-03-10
常规; C2; C2; Bob; 0; 2022-01-04
Gold; C3; C3; Carol; Carol; 0;
I have a CustomerRepository class:
public class CustomerRepository {
private static final String FILE_PATH = "src/poly/customer/data.txt";
public List<AbstractCustomer> customers;
{
try {
customers = readFiles();
} catch (IOException e) {
e.printStackTrace();
}
}
private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy");
public List<AbstractCustomer> readFiles() throws IOException{
List<AbstractCustomer> result = new ArrayList<>();
List<String> lines = Files.readAllLines(Path.of(FILE_PATH));
for (String line : lines) {
String[] parts = line.split(";");
int points = Integer.parseInt(parts[3]);
LocalDate date = LocalDate.parse(parts[4], formatter);
if (parts[0].equals("REGULAR")) {
RegularCustomer customer = new RegularCustomer(parts[1], parts[2], points, date);
result.add(customer);
} else if (parts[0].equals("GOLD")) {
GoldCustomer customer = new GoldCustomer(parts[1], parts[2], points);
result.add(customer);
} else {
throw new IOException();
}
}
return result;
}
I want to read customers from the file, and then add them to the customers List. I tried to do it like this :
{
try {
customers = readFiles();
} catch (IOException e) {
e.printStackTrace();
}
}
This gives me java.lang.NullPointerException: formatter, how can I fix this? This method should create objects from the text file and then add them to the customers list. My text file looks like this:
REGULAR;c1;Alice;0;2022-03-10
REGULAR;c2;Bob;0;2022-01-04
GOLD;c3;Carol;0;
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评论（1）
问题在于您的实例初始器（带有TR/CATCE语句的块）在
formatter的字段初始化器之前执行，因此格式>格式>格式>仍然是null。您可以只需移动
formatter上方的声明（包括初始化） instace Initializer ...但是我建议通过使用构造函数来简单地理解代码客户而不是实例初始器块。我还建议您制作
格式a static 字段 -dateTimeFormatter无论如何都是不变的，并且无论如何都可以在最终字段中存储，那么为什么为每个实例创建一个新的呢？ （这本身可以解决问题，但我仍然建议为了可读性使用普通的构造函数声明。）The problem is that your instance initializer (the block with the tr/catch statement) executes before the field initializer for
formatter, soformatteris still null.You could just move the declaration (including the initialization) of
formatterabove the instance initializer... but I would suggest making the code simpler to understand by using a constructor to initializecustomersinstead of the instance initializer block.I'd also recommend making
formattera static field -DateTimeFormatteris immutable and thread-safe anyway, you're storing it in a final field, so why create a new one for each instance? (That would fix the problem in itself, but I'd still suggest using a normal constructor declaration for the sake of readability.)