Java中如何创建仅指定特定字段的Transaction类对象并构建List集合

Hey there! Let's work through this problem together. The core issue here is that your current Transaction class only uses the default no-argument constructor, so you can't directly pass values for mnemonic, transactionCode, and timeStramp when creating new objects. Here are two easy-to-implement solutions:

方案1：添加带指定参数的构造方法 #

This is the most direct approach—we'll add a constructor to the Transaction class that accepts exactly the three fields you need to customize, while leaving the other fields with their default values.

修改后的Transaction类 #

import com.fasterxml.jackson.annotation.JsonProperty;

public class Transaction{ 
    @JsonProperty("Amount") 
    public String amount = "1390.00"; 
    @JsonProperty("Mnemonic") 
    public String mnemonic = "NYU"; 
    @JsonProperty("Transaction_Code") 
    public String transactionCode = "1435a"; 
    @JsonProperty("Time_Stramp") 
    public String timeStramp = "2021-02-16-22.50.41.782000"; 
    @JsonProperty("AccountNo") 
    public String accountNo = "15433276004350"; 

    // 添加带指定参数的构造方法
    public Transaction(String mnemonic, String transactionCode, String timeStramp) {
        this.mnemonic = mnemonic;
        this.transactionCode = transactionCode;
        this.timeStramp = timeStramp;
    }

    // 保留默认构造方法（Jackson序列化/反序列化会用到）
    public Transaction() {}
}

在Main类中创建5个对象并添加到List #

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Transaction> transactions = new ArrayList<>();
        
        // 对应示例数据逐个创建对象并添加
        transactions.add(new Transaction("PRY", "15s57", "2021-03-14-23.40.45.781300"));
        transactions.add(new Transaction("PCA", "16a48", "2021-04-21-17.30.15.331200"));
        transactions.add(new Transaction("PRY", "16t21", "2021-04-26-23.45.45.764100"));
        transactions.add(new Transaction("ASL", "17q02", "2021-05-12-18.20.25.232300"));
        transactions.add(new Transaction("RRL", "19m40", "2021-08-04-04.10.34.536400"));
    }
}

方案2：添加Setter方法（更灵活） #

If you prefer more flexibility (like being able to modify fields after creating the object), you can add setter methods for the three fields instead of a custom constructor.

修改后的Transaction类 #

import com.fasterxml.jackson.annotation.JsonProperty;

public class Transaction{ 
    @JsonProperty("Amount") 
    public String amount = "1390.00"; 
    @JsonProperty("Mnemonic") 
    public String mnemonic = "NYU"; 
    @JsonProperty("Transaction_Code") 
    public String transactionCode = "1435a"; 
    @JsonProperty("Time_Stramp") 
    public String timeStramp = "2021-02-16-22.50.41.782000"; 
    @JsonProperty("AccountNo") 
    public String accountNo = "15433276004350"; 

    // 添加Setter方法
    public void setMnemonic(String mnemonic) {
        this.mnemonic = mnemonic;
    }

    public void setTransactionCode(String transactionCode) {
        this.transactionCode = transactionCode;
    }

    public void setTimeStramp(String timeStramp) {
        this.timeStramp = timeStramp;
    }
}

在Main类中创建对象 #

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Transaction> transactions = new ArrayList<>();
        
        // 创建第一个对象并设置字段
        Transaction tx1 = new Transaction();
        tx1.setMnemonic("PRY");
        tx1.setTransactionCode("15s57");
        tx1.setTimeStramp("2021-03-14-23.40.45.781300");
        transactions.add(tx1);

        // 重复模式创建剩下的4个对象
        Transaction tx2 = new Transaction();
        tx2.setMnemonic("PCA");
        tx2.setTransactionCode("16a48");
        tx2.setTimeStramp("2021-04-21-17.30.15.331200");
        transactions.add(tx2);

        Transaction tx3 = new Transaction();
        tx3.setMnemonic("PRY");
        tx3.setTransactionCode("16t21");
        tx3.setTimeStramp("2021-04-26-23.45.45.764100");
        transactions.add(tx3);

        Transaction tx4 = new Transaction();
        tx4.setMnemonic("ASL");
        tx4.setTransactionCode("17q02");
        tx4.setTimeStramp("2021-05-12-18.20.25.232300");
        transactions.add(tx4);

        Transaction tx5 = new Transaction();
        tx5.setMnemonic("RRL");
        tx5.setTransactionCode("19m40");
        tx5.setTimeStramp("2021-08-04-04.10.34.536400");
        transactions.add(tx5);
    }
}

小提示 #

If you're using Java 16+, you could also make Transaction a record for even cleaner code, but since your original class uses default values and Jackson annotations, the above two methods are more compatible with your existing setup.

内容的提问来源于stack exchange，提问作者Deepika