如何將值複製到對象數組

Question

我創建了一個有幾個對象的類。

class SalesPerson { 
    String number; 
    String name; 
    double salesAmount; 
} 

所以現在我需要一些數據從文本文件複製到一個數組。

「sales.txt」

S0001 
Alice 
2000 
S0002 
Bob 
3400 
S0003 
Cindy 
1200 
S0004 
Dave 
2600 

下面是我的代碼的縮短版，假設的getName（S）的setName（S）和構造函數創建文本文件可以成功讀取：

class ArrayImport { 
    public static void main(String args[]) throws FileNotFoundException { 
     String fileName = "sales.txt"; 
     SalesPerson sp = new SalesPerson[4]; //Manually counted 

     //Read the file 
     Scanner sc = new Scanner(new FileReader(fileName)); 

     //Copy data to array 
     int i = 0; 
     while (sc.hasNext()) { 
      sp[i].name = sc.nextLine(); //Error starts here 
      sp[i].number = sc.nextLine(); 
      sp[i].salesAmount = Double.parseDouble(sc.nextLine()); 
      i++; 
     } 
    } 
} 

我收到錯誤消息「在線程異常‘主’顯示java.lang.NullPointerException ......」她指着我的評論「錯誤S上線撻這裏「。

所以我猜這不是給對象數組賦值的方法，如果我的猜測是正確的，那麼正確的語法是什麼？

Answer 1

對象的實例爲空，因此您必須先創建實例。所以創建像這樣的實例'staff [i] = new SalesPerson（）;' 我將實例創建添加到您的代碼中。

class ArrayImport { 
    public static void main(String args[]) throws FileNotFoundException { 
     String fileName = "sales.txt"; 
     SalesPerson sp = new SalesPerson[4]; //Manually counted 

     //Read the file 
     Scanner sc = new Scanner(new FileReader(fileName)); 

     //Copy data to array 
     int i = 0; 
     while (sc.hasNext()) { 
      staff[i] = new SalesPerson(); 
      staff[i].name = sc.nextLine(); //Error starts here 
      staff[i].number = sc.nextLine(); 
      staff[i].salesAmount = Double.parseDouble(sc.nextLine()); 
      i++; 
     } 
    } 
} 

Answer 2

工作例如：

public class ArrayImport { 

     public static void main(String[] args) throws FileNotFoundException { 
      List<SalesPerson> persons = new ArrayList<>(); 
      SalesPerson salesPerson = null; //Manually counted 

      //Read the file 
      Scanner scanner = new Scanner(new FileReader("sales.txt")); 

      int count=0; 
      while(scanner.hasNext()) { 
       if(count==0 || count%3 == 0) { 
        salesPerson = new SalesPerson(); 
        salesPerson.setNumber(scanner.nextLine()); 
        salesPerson.setName(scanner.nextLine()); 
        salesPerson.setSalesAmount(Double.parseDouble(scanner.nextLine())); 
        persons.add(salesPerson); 
        count+=3; 
       } 
      } 
      persons.forEach(person->System.out.println(person.toString())); 
     } 
    }