读取CSV文件时Project对象的Location字段输出null的问题排查

以下是几个最可能的原因及对应的修复方案：

1. 构造方法未正确赋值location成员变量 #

这是最常见的问题：你在Project的构造方法里接收了Location参数，但没有把它赋值给类的location成员变量。

错误示例：

public class Project {
    private String province;
    private String beneficiary;
    private Location location;

    // 错误：未给location成员变量赋值
    public Project(String province, String beneficiary, Location location) {
        this.province = province;
        this.beneficiary = beneficiary;
    }
}

修复：在构造方法中添加赋值语句

public Project(String province, String beneficiary, Location location) {
    this.province = province;
    this.beneficiary = beneficiary;
    this.location = location; // 关键：将参数赋值给成员变量
}

2. 成员变量被局部变量覆盖 #

如果在构造方法或其他方法中，你重新定义了同名的局部location变量，会导致类的成员变量始终未被赋值。

错误示例：

public Project(String province, String beneficiary, Location location) {
    this.province = province;
    this.beneficiary = beneficiary;
    Location location = location; // 局部变量覆盖了成员变量
}

修复：去掉局部变量的类型声明，直接使用this.location赋值

public Project(String province, String beneficiary, Location location) {
    this.province = province;
    this.beneficiary = beneficiary;
    this.location = location;
}

3. toString方法未正确引用成员变量 #

检查Project的toString方法，确保它引用的是类的location成员变量，而不是其他未初始化的变量或新创建的Location实例。

错误示例：

@Override
public String toString() {
    return "Project{" +
            "province='" + province + '\'' +
            ", beneficiary='" + beneficiary + '\'' +
            ", location=" + new Location() + // 错误：创建了新的空实例
            '}';
}

修复：直接引用成员变量location

@Override
public String toString() {
    return "Project{" +
            "province='" + province + '\'' +
            ", beneficiary='" + beneficiary + '\'' +
            ", location=" + location + // 正确引用成员变量
            '}';
}

4. 传入构造方法的是null而非初始化后的pLocation #

确认processLine方法中，你传入Project构造的是已经正确初始化的pLocation实例，而不是null或未赋值的变量。

错误示例：

// 错误：传入了null
Project pProject = new Project(province, beneficiary, null);

正确写法：

// 先初始化pLocation，再传入构造方法
Location pLocation = new Location(latitude, longitude);
Project pProject = new Project(province, beneficiary, pLocation);

内容的提问来源于stack exchange，提问作者Cindy_l