類和文件異常錯誤

Question

我的電腦上有一個名爲records.txt的文件，上面有幾行文字。每行的格式爲 「姓名 - 姓氏 - 地址 - 年齡 - GPA」

亞當 - 邁克爾 - 佛羅里達州蓋恩斯維爾 - 16 - 75

愛麗絲 - 巴里 - 佛羅里達州傑克遜維爾 - 17 - 40

凱文 - 亞當 - 佛羅里達州奧蘭多 - 20 - 65

雅各布 - 邁克爾 - 佛羅里達州邁阿密 - 16 - 88

塞布麗娜 - 馬修 - 佛羅里達州蓋恩斯維爾 - 18 - 90

我的程序應該將這些信息分開，並使用一組學生來顯示信息。 cgpa是由我的gpa代碼中顯示的界限給出的字母等級。這是我的代碼給我的錯誤。

 Exception in thread "main" java.lang.NullPointerException 
at hw6_hamilton_daniel.HW6_Hamilton_Daniel.main(HW6_Hamilton_Daniel.java:41) 
C:\Users\dhami\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1 
BUILD FAILED (total time: 0 seconds) 

這裏是我的編碼：

MAIN：

package hw6_hamilton_daniel; 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.util.Scanner; 
/** 
* 
* @author dhami 
*/ 
public class HW6_Hamilton_Daniel { 

/** 
* @param args the command line arguments 
*/ 
public static void main(String[] args) { 

    try { 

     File records = new File("C:\\Users\\dhami\\Desktop\\records.txt"); 
     Scanner input = new Scanner(records); 

     int count = 0; 
     while (input.hasNextLine()) { 
      count = count + 1; 
      break; 
     } 
     input.close(); 

     student[] students = new student[count]; 
     Scanner input2 = new Scanner(records); 

     for (int i = 0; i < count; i++) { 

      String line = input2.nextLine(); 
      String[] Split = line.split(" - "); 

      students[i].set_firstname(Split[0]); 
      students[i].set_lastname(Split[1]); 
      students[i].set_address(Split[2]); 
      students[i].set_age(Split[3]); 
      students[i].set_gpa(Split[4]); 

      students[i].Display_info(); 
      break; 
     } 
     input2.close(); 
    } catch (FileNotFoundException ex) { 
     System.out.println("File Not Found"); 
    }//IF FILE IS NOT ON MACHINE 

} 

}

類：

public class student { 

private String firstname; 
private String lastname; 
private String address; 
private int age; 
private int gpa; 
private char cgpa; 

student() { 
    firstname = "Default_FName"; 
    lastname = "Default_LName"; 
    address = "Default_Address"; 
    age = 0; 
    gpa = 0; 
    cgpa = 'X'; 
}//Default constructor 

void set_firstname (String new_name) { 
    firstname = new_name; 
} 
String get_firstname() { 
    return firstname; 
}//firstname------------- 

void set_lastname (String new_lastname) { 
    lastname = new_lastname; 
} 
String get_lastname() { 
    return lastname; 
}//lastname-------------- 

void set_address (String new_address) { 
    address = new_address; 
} 
String get_address() { 
    return address; 
}//address--------------- 

void set_age (String new_age) { 
    age = Integer.parseInt(new_age); 
} 
int get_age() { 
    return age; 
}//age------------------- 

void set_gpa (String new_gpa) { 
    gpa = Integer.parseInt(new_gpa); 

    if (gpa >= 85 && gpa <= 100) { 
     cgpa = 'A'; 
    } 
    if (gpa >=60 && gpa <= 85) { 
     cgpa = 'B'; 
    } 
    else { 
     cgpa = 'C'; 
    } 
} 
int get_gpa() { 
    return gpa; 
}//gpa------------------- 
char get_cgpa() { 
    return cgpa; 
} 

void Display_info() { 
    System.out.println("First Name: "+firstname); 
    System.out.println("Last Name: "+lastname); 
    System.out.println("Address: "+address); 
    System.out.println("Age: "+age); 
    System.out.println("GPA: "+gpa+" ("+cgpa+")\r\n"); 
} 
    } 

Answer 1

我創建類的實例，以避免靜電上下文。

基本上學生[我]沒有任何價值，我已經初始化它作爲一個新的Student對象

public class HW6_Hamilton_Daniel { 

public static void main(String[] args) { 
    new HW6_Hamilton_Daniel().run(); 
} 

public void run() { 
Student[] students = new Student[5]; 
    int i = 0; 
      String line = "Adam - Michael - Gainesville florida - 16 - 75"; 
      String[] Split = line.split(" - "); 

    students[i] = new Student(); 
      students[i].set_firstname(Split[0]); 
      students[i].set_lastname(Split[1]); 
      students[i].set_address(Split[2]); 
      students[i].set_age(Split[3]); 
      students[i].set_gpa(Split[4]); 
      students[i].Display_info(); 
} 

class Student { 

private String firstname; 
private String lastname; 
private String address; 
private int age; 
private int gpa; 
private char cgpa; 

Student() { 
    firstname = "Default_FName"; 
    lastname = "Default_LName"; 
    address = "Default_Address"; 
    age = 0; 
    gpa = 0; 
    cgpa = 'X'; 
}//Default constructor 

void set_firstname (String new_name) { 
    firstname = new_name; 
} 
String get_firstname() { 
    return firstname; 
}//firstname------------- 

void set_lastname (String new_lastname) { 
    lastname = new_lastname; 
} 
String get_lastname() { 
    return lastname; 
}//lastname-------------- 

void set_address (String new_address) { 
    address = new_address; 
} 
String get_address() { 
    return address; 
}//address--------------- 

void set_age (String new_age) { 
    age = Integer.parseInt(new_age); 
} 
int get_age() { 
    return age; 
}//age------------------- 

void set_gpa (String new_gpa) { 
    gpa = Integer.parseInt(new_gpa); 

    if (gpa >= 85 && gpa <= 100) { 
     cgpa = 'A'; 
    } 
    if (gpa >=60 && gpa <= 85) { 
     cgpa = 'B'; 
    } 
    else { 
     cgpa = 'C'; 
    } 
} 
int get_gpa() { 
    return gpa; 
}//gpa------------------- 
char get_cgpa() { 
    return cgpa; 
} 

void Display_info() { 
    System.out.println("First Name: "+firstname); 
    System.out.println("Last Name: "+lastname); 
    System.out.println("Address: "+address); 
    System.out.println("Age: "+age); 
    System.out.println("GPA: "+gpa+" ("+cgpa+")\r\n"); 
} 
    } 

}