java - 如何读取txt到arrayList然后返回arrayList？

Question

我需要将文件读入 arrayList 并返回 arrayList，但我在放入对象时遇到困难。我不断收到此错误:

Type mismatch: cannot convert from ArrayList to ArrayList

*不允许改变方法

我尝试将 ArrayList 放入 ArrayList

public static ArrayList<Names> readEntrees(String fileName) {
    String filename = "data/names.txt";

    ArrayList<String> myNames = new ArrayList<String>();

    try {
    BufferedReader br = new BufferedReader(new FileReader("names.txt"));

    String line = null;

    while ((line = br.readLine()) != null) {
        //take each line and split them around @@
        String[] elements = line.split("@@");
        //convert the string[] to an arraylist
        myNames = new ArrayList< String>(Arrays.asList(elements));
        myNames.add(line);
    }

    br.close();
    return (myNames);
}

Type mismatch: cannot convert from ArrayList to ArrayList

Answer 1

您需要将字符串列表转换为名称列表。所以，让我们使用一个简单的 Name 类(我必须弥补这个，因为我没有你的类代码):

public class Name {
    String name;

    public Name(String name) {
        this.name = name;
    } 

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "Name [name=" + name + "]";
    }    
}

这里我们可以使用new Name(text)将字符串转换为Name对象。构造函数。因此，让我们让您的方法返回 List<Name> ，不是 ArrayList<Name>因为前者会做后者会做的所有事情，但具有更大的灵 active (接口(interface)代码等)，然后使用 Streams，我们可以将字符串数据转换为 List<Name> :

public static List<Name> readEntries(String filename) throws IOException {

    // String filename = "data/names.txt"; // this makes **no sense**. get rid of it

    List<Name> result = null;
    // code to read in text
    File file = new File(filename);
    result = Files.lines(file.toPath()).map(Name::new).collect(Collectors.toList());

    return result;
}

代码已更正为使用 "@@" 分割每一行，并根据 AjahnCharles 进行改进:

public static List<Name> readEntries(String filename) throws IOException {
    List<Name> result = null;
    // code to read in text
    result = Files.lines(Paths.get(filename)) // get each line from file
            .flatMap(Pattern.compile("@@")::splitAsStream) // split each line into stream
            .map(Name::new) // map each String into Name
            .collect(Collectors.toList()); // collect into List

    return result;
}

测试程序:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class TestNameList {
    public static void main(String[] args) {
        // TODO: use actual path String to file
        String fileName = "src/pkg3/Names.txt";
        try {
            List<Name> names = readEntries(fileName);
            names.stream().forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    public static List<Name> readEntries(String filename) throws IOException {
        List<Name> result = null;
        // code to read in text
        result = Files.lines(Paths.get(filename)) // get each line from file
                .flatMap(Pattern.compile("@@")::splitAsStream) // split each line into stream
                .map(Name::new) // map each String into Name
                .collect(Collectors.toList()); // collect into List

        return result;
    }
}