Question

我正在编写一个应用程序，当用户输入文件所在的URL地址时，该应用程序从URL读取文件。它将读取数据值，然后将数据值输入到每个类对象。当我写setText命令（在while循环之外）时，当我输入e1.getName（）时会出错。它要求我初始化e1。我这样做了，但是当我运行应用程序时，getName（）显示为null。我想要员工的名字。所以，首先是这个类是什么样的：

public class Employee {
        private String name;
        private double salary;
        private String id;
        private String office;
        private String extension;
        private int yearsofservice;

//default constructor
Employee(String string, double d, String string2, String string3, String string4, int i)
{
}

//copy constructor
Employee(Employee eData)
{
name = eData.name;
salary = eData.salary;
id = eData.id;
office = eData.office;
extension = eData.extension;
yearsofservice = eData.yearsofservice;
}
//Define the methods
public String getName()
{
//Return the object's name
return name;
}
public void setName(String n)
{
//set the object's name to the given name
name = n;
}
public double getSalary()
{
return salary;
}
public void setSalary(double s)
{
salary = s;
}
public String getId()
{
return id;
}
public void setId(String ID)
{
id = ID;
}
public String getOffice()
{
return office;
}
public void setOffice(String o)
{
office = o;
}
public String getExtension()
{
return extension;
}
public void setExtension(String e)
{
extension = e;
}
public int getYearsOfServ()
{
return yearsofservice;
}
public void setYearsOfServ(int yos)
{
yearsofservice = yos;
}

}

其次，这是MainActivity中的代码或app的代码：

public void displayEmployees(View view)
   {
    EditText edt1;
    TextView tv;
    String urlfile;

    //Declare three references to Employee object
    Employee e1;
    Employee e2;
    Employee e3;



    //Create reference for EditText and TextView

    edt1 = (EditText) findViewById(R.id.edit_file);

    tv = (TextView) findViewById(R.id.text_main);

    //Store the URL address when user input it and assign the input
    //to variable (reference) urlfile 
    urlfile = edt1.getText().toString();

    //Use try/catch to check if the file opening on the web succeed
    try
    {
        //Create an URL object that read urlfile
        URL file_url = new URL(urlfile);

        //try to open the file from the web
        Scanner fsc = new Scanner(file_url.openStream());

        //As long as there is data to read, continue
        //reading the file
        while(fsc.hasNext())
        {

            //tv.append("\n" + fsc.nextLine());//This is for testing to display data

            //Create three Employee objects and input the data values
            //from urlfile to each object
            e1 = new Employee(fsc.nextLine(), Double.parseDouble(fsc.nextLine()), 
                    fsc.nextLine(), fsc.nextLine(), fsc.nextLine(), 
                    Integer.parseInt(fsc.nextLine()));

            e2 = new Employee(fsc.nextLine(), Double.parseDouble(fsc.nextLine()), 
                    fsc.nextLine(), fsc.nextLine(), fsc.nextLine(), 
                    Integer.parseInt(fsc.nextLine()));

            e3 = new Employee(fsc.nextLine(), Double.parseDouble(fsc.nextLine()), 
                    fsc.nextLine(), fsc.nextLine(), fsc.nextLine(), 
                    Integer.parseInt(fsc.nextLine()));

            //e1.setOffice(Integer.parseInt(data));
            //...Continue with other class objects with their respective set method
        } 

        tv.setText("The name of the employee: " + e1.getName()); //The error is here!

    }
    catch(IOException e)
    {
        tv.setText("Error: Invalid URL Address or File Does Not Exist");
    }


}

}

最后，文件看起来像这样（注意：每个值都在一个单独的行中）：莎莉史密斯 086244 100000.00 Ramsey Hall 3814 9976 9 露西拜耳 288567 39500.57 Cullimore Hall 100 6000 1 威廉哈里斯 732241 120000.00 GITC 165 7533 4

Answer 1

fsc可能没有下一个元素（while循环不会启动e1）。写System.out.println（“text”）;在while循环中并告诉它是否被调用。

Answer 2

您在while循环中使用的Employee构造函数不会对您提供的数据执行任何操作。因此，您永远不会在Employee对象上获得任何名称

public Employee(String name , double salary, String id, String office, String extension, int yearsofservice)
{
    this.name = name;
    this.salary = salary;
    this.id = id;
    this.office = office;
    this.extension = extension;
    this.yearsofservice = yearsofservice;
}

如何获得对象e1的正确输出？

2 个答案: