如何更新文本文件中的特定数字？

为了调整解决方案，我不得不对一些变量进行重新排序。

我将 log 和 tenantData 移动到另一个类。

我的第一个建议是使用不同的分隔符来分隔租户数据 .txt 文件中的值。
这将使与文件之间的解析变得更加容易，因为数据包含逗号。

您可以改用制表符。
这是一个参考，维基百科 - 制表符分隔值。

由于您正在使用 toString 来生成输出，因此可以将其替换为以下内容。

@Override
public String toString() {
    return firstName + ' ' + lastName + '\t'
        + apartmentNumber + '\t'
        + streetNumber + ' ' + streetAddress + '\t'
        + town + ", " + state + '\t'
        + monthRent + '\t'
        + balance;
}

此外，还需要一种方法将行转换为 Person 对象。
可以向 Person 类添加静态分析方法。

static Person parse(String string) {
    Person person = new Person();
    String[] strings = string.split("\t", -1);
    int indexOf = strings[0].indexOf(' ');
    person.firstName = strings[0].substring(0, indexOf);
    person.lastName = strings[0].substring(indexOf + 1);
    person.apartmentNumber = Integer.parseInt(strings[1]);
    indexOf = strings[2].indexOf(' ');
    person.streetNumber = Integer.parseInt(strings[2].substring(0, indexOf));
    person.streetAddress = strings[2].substring(indexOf + 1);
    indexOf = strings[3].indexOf(", ");
    person.town = strings[3].substring(0, indexOf);
    person.state = strings[3].substring(indexOf + 2);
    person.monthRent = Float.parseFloat(strings[4]);
    person.balance = Float.parseFloat(strings[5]);
    return person;
}

而且，我们需要一种方法来比较 Person 对象。
这也是在 Person 类中。

boolean equals(Person person) {
    return firstName.equals(person.firstName)
        && lastName.equals(person.lastName)
        && apartmentNumber == person.apartmentNumber
        && streetNumber == person.streetNumber
        && streetAddress.equals(person.streetAddress)
        && town.equals(person.town)
        && state.equals(person.state);
}

从这里，您需要创建功能来读取文件，并找到正确的行。
有几种方法可以实现这一点。我通常使用 BufferedReader 类，因为它提供了 readLine 方法。
您还可以使用 Scanner 类，NIO 框架也提供了 Paths 和 Files 类——实际上，我在下面使用它们来编写文件。

我将此方法与 log 和 tenantData 变量一起放在另一个类中。

请注意，由于 Person 对象的唯一性依赖于许多变量，因此我使用 Person 对象作为要匹配的参数。
而不是为每个单独的值设置一个参数。

/** @return null if not found */
Person find(Person person) throws IOException {
    try (BufferedReader reader = new BufferedReader(new FileReader(log))) {
        String line;
        Person value;
        while ((line = reader.readLine()) != null) {
            if (person.equals(value = Person.parse(line)))
                return value;
        }
        return null;
    }
}

因此，您可以根据需要从此处更新 Person 对象的值。

其中，您需要一种方法将数据写回文件中。

我发现 Google AI 有一个有趣的方法，它建议我使用 String#replace 来覆盖原始值。

void save(Person original, Person updated) throws IOException {
    String string = new String(Files.readAllBytes(log.toPath()));
    string = string.replace(original.toString(), updated.toString());
    try (FileWriter writer = new FileWriter(log)) {
        writer.write(string);
        writer.flush();
    }
}

下面是一个基本示例，我在其中创建了包含 3 个 Person 对象的文件，然后更新了一个对象并保存它。

tenantData = new ArrayList<>();
tenantData.add(new Person("firstNameA", "lastNameA", 1, "addressA", 1, "townA", "stateA", 1, 1));
tenantData.add(new Person("firstNameB", "lastNameB", 1, "addressB", 1, "townB", "stateB", 2, 2));
tenantData.add(new Person("firstNameC", "lastNameC", 1, "addressC", 1, "townC", "stateC", 3, 3));

try (FileWriter writer = new FileWriter("files/tenantData.txt")) {
    for (Person person : tenantData)
        writer.write(person.toString() + System.lineSeparator());
    writer.flush();
}

Example example = new Example();

System.out.println("original");
for (String line : Files.readAllLines(example.log.toPath()))
    System.out.println(line);

Person person = example.find(new Person("firstNameB", "lastNameB", 1, "addressB", 1, "townB", "stateB", 0, 0));
Person copy = Person.parse(person.toString());
person.balance += 10;

example.save(copy, person);

System.out.println();
System.out.println("updated");
for (String line : Files.readAllLines(example.log.toPath()))
    System.out.println(line);

输出

original
firstNameA lastNameA    1   1 addressA  townA, stateA   1.0 1.0
firstNameB lastNameB    1   1 addressB  townB, stateB   2.0 2.0
firstNameC lastNameC    1   1 addressC  townC, stateC   3.0 3.0

updated
firstNameA lastNameA    1   1 addressA  townA, stateA   1.0 1.0
firstNameB lastNameB    1   1 addressB  townB, stateB   2.0 12.0
firstNameC lastNameC    1   1 addressC  townC, stateC   3.0 3.0

而且，这是完整的代码。

public class Example {
    File log = new File("tenantData.txt");
    static ArrayList<Person> tenantData = new ArrayList<Person>();

    /** @return null if not found */
    Person find(Person person) throws IOException {
        try (BufferedReader reader = new BufferedReader(new FileReader(log))) {
            String line;
            Person value;
            while ((line = reader.readLine()) != null) {
                if (person.equals(value = Person.parse(line)))
                    return value;
            }
            return null;
        }
    }

    void save(Person original, Person updated) throws IOException {
        String string = new String(Files.readAllBytes(log.toPath()));
        string = string.replace(original.toString(), updated.toString());
        try (FileWriter writer = new FileWriter(log)) {
            writer.write(string);
            writer.flush();
        }
    }

    static class Person {
        public String firstName;
        public String lastName;
        public int apartmentNumber;
        public String streetAddress;
        public int streetNumber;
        public String town;
        public String state;
        public float balance;
        public float deposit;
        public float monthRent;

        Person() {
        }

        Person(String firstName, String LastName, int apartmentNumber, String streetAddress, int streetNumber, String town, String state, float monthRent, float balance) {

            this.firstName = firstName;
            this.lastName = LastName;
            this.apartmentNumber = apartmentNumber;
            this.streetAddress = streetAddress;
            this.streetNumber = streetNumber;
            this.town = town;
            this.state = state;
            this.monthRent = monthRent;
            this.balance = balance;

        }

        static Person parse(String string) {
            Person person = new Person();
            String[] strings = string.split("\t", -1);
            int indexOf = strings[0].indexOf(' ');
            person.firstName = strings[0].substring(0, indexOf);
            person.lastName = strings[0].substring(indexOf + 1);
            person.apartmentNumber = Integer.parseInt(strings[1]);
            indexOf = strings[2].indexOf(' ');
            person.streetNumber = Integer.parseInt(strings[2].substring(0, indexOf));
            person.streetAddress = strings[2].substring(indexOf + 1);
            indexOf = strings[3].indexOf(", ");
            person.town = strings[3].substring(0, indexOf);
            person.state = strings[3].substring(indexOf + 2);
            person.monthRent = Float.parseFloat(strings[4]);
            person.balance = Float.parseFloat(strings[5]);
            return person;
        }

        boolean equals(Person person) {
            return firstName.equals(person.firstName)
                && lastName.equals(person.lastName)
                && apartmentNumber == person.apartmentNumber
                && streetNumber == person.streetNumber
                && streetAddress.equals(person.streetAddress)
                && town.equals(person.town)
                && state.equals(person.state);
        }

        @Override
        public String toString() {
            return firstName + ' ' + lastName + '\t'
                + apartmentNumber + '\t'
                + streetNumber + ' ' + streetAddress + '\t'
                + town + ", " + state + '\t'
                + monthRent + '\t'
                + balance;
        }
    }
}