这是我的保存方法
public static void save() {
try {
PrintWriter myWriter = new PrintWriter("database.txt");
for(int i=0; i<people.size(); i++) {
myWriter.println(people.get(i).toString());
}
myWriter.close();
System.out.println("Successfully wrote to the file.");
menu();
} catch (IOException e) {
System.out.println("An error occurred.");
e.printStackTrace();
}
}
这是文件中的样子
Donald Trump 23323.00
这是arraylist的字段和名称
ArrayList<Person> people = new ArrayList<Person>();
public Person(String name, String password, double money) {
this.name = name;
this.password = password;
this.money = money;
}
constructors below.....
如何读取该文件并将其存储在对象的arraylist中？需要帮助：D
答案 0 :(得分：1)
并非您写入数据文本文件的方式有什么问题，只是我认为最好遵循一种更常规的CSV样式文件格式，该格式专用于此数据存储类型。
例如，CSV文件中的每一行都被视为一条记录行，通常用逗号（，）分隔该行中字段数据的列，而不是空格或制表符（如文件中的空格），并且显然是有充分理由的。最终，将需要检索文件中的数据，如果列字段中包含空格怎么办？例如，某些姓氏包含两个单词（Simone de Beauvoir，Herbert M. Turner III，Ashley M. St. John等）。必须对此进行一些考虑，是的，肯定有解决方法，但总的来说，利用除空格以外的更具体的定界符会更容易。您可能需要考虑将空格定界符更改为逗号或分号定界符。您甚至可以在 Person 类 toString（）方法中将其作为选项提供：
/* Example Person Class... */
import java.io.Serializable;
public class Person implements Serializable {
// Default serialVersion id
private static final long serialVersionUID = 1212L;
private String name;
private String password;
private double money;
public Person() { }
public Person(String name, String password, double money) {
this.name = name;
this.password = password;
this.money = money;
}
public String toString(String delimiterToUse) {
return new StringBuffer("").append(this.name).append(delimiterToUse)
.append(this.password).append(delimiterToUse)
.append(String.format("%.2f", this.money)).toString();
}
@Override
public String toString() {
return new StringBuffer("").append(this.name).append(" ")
.append(this.password).append(" ")
.append(String.format("%.2f", this.money)).toString();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public double getMoney() {
return money;
}
public void setMoney(double money) {
this.money = money;
}
}
在您的 save（）方法中，您可能已有一行使用空白的类默认定界符（" "）
myWriter.println(people.get(i).toString());
或使用其他分隔符，例如逗号/空格组合（", "）：
myWriter.println(people.get(i).toString(", "));
文件中的数据记录如下所示：
Donald Trump, myPassword, 23323.0
现在，使用类似String#split()这样的方法，可以更轻松地分析上方的数据行，例如：
public static List<Person> readInPeople(String databaseFile) {
/* Declare a List Interface to hold all the read in records
of people from the database.txt file. */
List<Person> people = new ArrayList<>();
// 'Try With Resouces' is used to so as to auto-close the reader.
try (BufferedReader reader = new BufferedReader(new FileReader("database.txt"))) {
String dataLine;
while ((dataLine = reader.readLine()) != null) {
dataLine = dataLine.trim();
// Skip past blank lines.
if (dataLine.equals("")) {
continue;
}
/* Split the read in dataline delimited field values into a
String Array. A Regular Expression is used within the split()
method that takes care of any comma/space delimiter combination
situation such as: "," or ", " or " ," or " , " */
String[] dataLineParts = dataLine.split("\\s{0,},\\s{0,}");
// Ensure defaults for people.
String name = "", password = "";
double money = 0.0d;
/* Place each split data line part into the appropriate variable
IF it exists otherwise the initialized default (above) is used. */
if (dataLineParts.length >= 1) {
name = dataLineParts[0];
if (dataLineParts.length >= 2) {
password = dataLineParts[1];
if (dataLineParts.length >= 3) {
/* Make sure the data read in is indeed a string
representation of a signed or unsigned Integer
or double/float type numerical value. The Regular
Expression within the String#matches() method
does this. */
if (dataLineParts[2].matches("-?\\d+(\\.\\d+)?")) {
money = Double.parseDouble(dataLineParts[2]);
}
}
}
}
// Add the person from file into the people List.
people.add(new Person(name, password, money));
}
}
// Catch Exceptions...
catch (FileNotFoundException ex) {
System.err.println(ex.getMessage());
}
catch (IOException ex) {
System.err.println(ex.getMessage());
}
/* Return the list of people read in from the
database text file. */
return people;
}
要使用此方法，您可以执行以下操作：
// Call the readInPeople() method to fill the people List.
List<Person> people = readInPeople("database.txt");
/* Display the people List in Console Window
using a for/each loop. */
// Create a header for the data display.
// Also taking advantage of the String#format() and String#join() methods.
// String#join() is used to create the "=" Header underline.
String header = String.format("%-20s %-15s %s\n", "Name", "Password", "Money");
header += String.join("", Collections.nCopies(header.length(), "="));
System.out.println(header);
// Display the list. Also taking advantage of the printf() method.
for (Person peeps : people) {
System.out.printf("%-20s %-15s %s\n", peeps.getName(), peeps.getPassword(),
String.format("%.2f", peeps.getMoney()));
}
控制台显示如下：
Name Password Money
===========================================
Donald Trump myPassword 23323.00
Tracey Johnson baseball 2233.00
Simone de Beauvoir IloveFrance 32000.00
答案 1 :(得分：0)
逐行读取文件，并使用与toString类的Person中使用的定界符相同。
就像：假设您使用" "作为分隔符。
然后read line by line并使用该定界符分割数据并分别转换数据
String line = reader.readLine();
String[] array = line.split(" ")// use same delimiter used to write
if(array.lenght() ==3){ // to check if data has all three parameter
people.add(new Person(array[0], array[1], Double.parseDouble(array[2])));
// you have to handle case if Double.parseDouble(array[2]) throws exception
}