Question

我是Java的完全入门者，我进行了一次练习，我必须从CSV文件中读取数据，然后在程序从文件中读取数据时为文件的每一行创建一个对象。 / p>

这是CSV文件的一部分：

1,Jay, Walker,91 Boland Drive,BAGOTVILLE,NSW,2477
2,Mel, Lowe,45 Ocean Drive,MILLERS POINT,NSW,2000
3,Hugh, Manatee,32 Edgecliff Road,REDFERN,NSW,2016
4,Elizabeth, Turner,93 Webb Road,MOUNT HUTTON,NSW,2290

以此类推...

这是我的代码，可从CSV文件读取数据：

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Client_19918424 {

    public static void main(String[] args) throws FileNotFoundException {
        File inFile = new File("clients.txt");
        Scanner inputFile = new Scanner(inFile);
        String str;
        String[] tokens;
        while (inputFile.hasNext()) {
            str = inputFile.nextLine();         // read a line of text from the file 
            tokens = str.split(",");            // split the line using commas as delimiter
            
            System.out.println("Client ID: " + tokens[0]);
            System.out.println("Client First Name: " + tokens[1]);
            System.out.println("Client Sur Name: " + tokens[2]);
            System.out.println("Street Address: " + tokens[3]);
            System.out.println("Suburb: " + tokens[4]);
            System.out.println("State: " + tokens[5]);
            System.out.println("Postcode:" + tokens[6]);
            System.out.println( );
                
        } // end while
    }
}

这是我的Client类（具有构造函数）：

public class Client {
    private int clientID;
    private String firstName;
    private String surName;
    private String street;
    private String suburb;
    private String state;
    private int postcode;
    
    // constructor
    public Client (int ID, String fName, String sName, String str, String sb, String sta, int pCode) {
        
        clientID = ID;
        firstName = fName;
        surName = sName;
        street = str;
        suburb = sb;
        state = sta;
        postcode = pCode;
    }

但是，当程序从文件中读取数据时，我不知道如何为文本文件的每一行创建一个Client对象。像第一行这样：

Client client1 = new Client(1, "Jay", "Walker", "91 Boland Drive", "BAGOTVILLE", "NSW", 2477);

然后将其添加到数组：

Client[0] = client1;

有人可以帮我解决这个问题，我真的很感激。

Answer 1

您快到了。剩下要做的就是将每个已打印的令牌映射到Client类中的相应字段。由于token[0]并没有真正说出它拥有什么价值，您可以通过三种方式做到这一点：

 while (inputFile.hasNext()) {
    str = inputFile.nextLine();        
    tokens = str.split(",");           
    // Because tokens[0] is of type String but clientID is of type int,
    // we need to parse it and get the integer representation.
    int clientID = Integer.parseInt(tokens[0]);
    // Both of type String, no parsing required.
    String firstName = tokens[1];
    String surName = tokens[2];
    String street = tokens[3];
    String suburb = tokens[4];
    String state = tokens[5];
    int postcode = Integer.parseInt(tokens[6]);
    // Then all that's left to do is to create a new object of `Client` type
    // and pass all the gathered information.
    Client client = new Client(clientID, firstName, surName, street, suburb, state, postcode);
    System.out.println(client + "\n");
}

这时，如果我们尝试打印客户端（最后一行），我们将得到如下内容：com.example.demo.Client@30a3107a。那是因为我们没有告诉我们如何显示对象。对于toString()类中的Client方法，必须这样重写：

@Override
public String toString() {
    return "Client ID: " + clientID + "\n" + "Client First Name: " + firstName + "\n" 
           + "Client Sur Name: " + surName + "\n" + "Street Address: " + street + "\n" 
           + "Suburb: " + suburb + "\n" + "State: " + state + "\n" + "Postcode: " + postcode;
}

它将给出示例中的确切输出。

也可以通过直接传递这些标记来创建类，而无需创建临时变量：

Client client = new Client(Integer.parseInt(tokens[0]), tokens[1], tokens[2], tokens[3], tokens[4], tokens[5], Integer.parseInt(tokens[6]));

这种情况将我们带到使用setter和getter的第三个解决方案。描述Client的变量已经定义，可以传递它们来组装完美的对象，但是无法检索它们。代替直接在构造函数中设置变量，我们可以创建一个可以完成此任务的特殊方法，例如：

// Other fields omitted
private int clientID;

// The empty constructor required for later usage,
// since right now, we can't create the object without specifying every property.
public Client() {
}

// This method does exactly the same thing that was done before but
// in the constructor directly
public void setClientID(int clientID) {
    this.clientID = clientID;
}

// This method will assist in retrieving the set data from above.
public int getClientID() {
    return clientID;
}

然后while loop看起来像这样：

Client client = new Client();
client.setClientID(Integer.parseInt(tokens[0]));
client.setFirstName(tokens[1]);
client.setSurName(tokens[2]);
client.setStreet(tokens[3]);
client.setSuburb(tokens[4]);
client.setState(tokens[5]);
client.setPostcode(Integer.parseInt(tokens[6]));

并获得这些值：

System.out.println("Client ID: " + client.getClientID());

或者，如果只能在所有字段都存在的情况下创建客户端，则可以将构造函数与字段一起使用来创建客户端，在类中添加getter，省略两个setter，以及空的构造函数。 >

从CSV文件读取并创建对象

1 个答案: