Question

我已经在这几个小时了，我有点沮丧。如果有人愿意看看我的代码并告诉我为什么我不能在StudentRecWithinput.Update（）中使用Student1，我会很乐意伸出援助之手;

它在没有它的情况下工作，但它似乎只使用我正在阅读的最后一行数据。

MAIN

package Database;

import java.io.FileNotFoundException;
import java.util.Scanner;

public class Main {

public static void main(String[] args) throws FileNotFoundException {
    Scanner Keyboard = new Scanner(System.in);
    String choice1 = "";

    System.out
            .println("Would you like to update a students GPA? Please Input Yes or NO.");
    choice1 = Keyboard.next();

    if (choice1.charAt(0) == 'y' || choice1.charAt(0) == 'Y') {
        recupdate();
    } else {
        System.out.println("Alright, Goodbye!");
    }
}

public static void recupdate() throws FileNotFoundException {
    Scanner Keyboard = new Scanner(System.in);
    int choice2;
    System.out.println("Here are the records!\n");

    StudentRec Student1 = new StudentRec();
    StudentRec Student2 = new StudentRec();
    StudentRec Student3 = new StudentRec();

    System.out
            .println("Who's gpa will you be edditing? Please input (1, 2 or 3)");

    choice2 = Keyboard.nextInt();
    if (choice2 == 1) {

        StudentRecWithInput.update(Student1);

    }

    if (choice2 == 2) {
        StudentRecWithInput.update(Student2);
    }

    if (choice2 == 3) {
        StudentRecWithInput.update(Student3);

    }
}
}

STUDENTREC

package Database;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class StudentRec {
// student related//

private String lastname;
private String firstname;
private String major;
private int age;
private static double gpa;
private static int credit;

// /non student related////
File info = new File("studentinfo.txt");
Scanner scan = new Scanner(info);
static int count = 0;

public StudentRec() throws FileNotFoundException {

    {
        count++;

        if (count == 2) {
            scan.nextLine();

        }

        else if (count == 3) {
            scan.nextLine();
            scan.nextLine();
        }

        firstname = scan.next();
        lastname = scan.next();
        age = scan.nextInt();
        setGpa(scan.nextDouble());
        major = scan.next();
        setCredit(scan.nextInt());
        System.out.println(firstname + " " + lastname + " " + age + " "
                + getGpa() + " " + major + " " + getCredit() + "");

    }

}

public static int getCredit() {
    return credit;
}

public void setCredit(int credit) {
    this.credit = credit;
}

public static double getGpa() {
    return gpa;
}

public void setGpa(double gpa) {
    this.gpa = gpa;
}

}

STUDENTRECWITHINPUT

package Database;

import java.io.FileNotFoundException;
import java.util.Scanner;

public class StudentRecWithInput extends StudentRec {
static Scanner keyboard = new Scanner (System.in);


public StudentRecWithInput() throws FileNotFoundException {
    super();



}

public static double update(int credit, double gpa)
{
    double pastpoints = getCredit() * getGpa();
    int newcredhours = keyboard.nextInt();
    double newpoint = keyboard.nextDouble();
    double semestergpa = newpoint / newcredhours;
    double cumulate = (pastpoints + newpoint) / (newcredhours+ getCredit());

    System.out.print(pastpoints);

    return cumulate;

}

}

studentinfo.txt

Bob Bobbers 19 3.5 CPS 55 
John Johners 20 3.7 BIO 70
Kat Katters 21 3.8 ITC 100

Answer 1

StudentRecWithInput的签名

update(int credit, double gpa)

期望int和double，但是你用

调用它

StudentRecWithInput.update(Student1);

您需要将签名更改为：

update(StudentRec student)

能够将学生信息传递给方法。

您还应该阅读有关静态和非静态方法之间差异的更多信息，因为现在您的代码没有编译更改。

Answer 2

您可能想要调整策略。请考虑使用以下步骤：

将您的输入文件读入VectorRecord的Vector。（每次创建StudentRec时，您的代码都会尝试准备输入文件）
然后询问应更新哪条记录
然后询问该记录的更新数据

所以你的主人可能有Vector<StudentRec>

当您需要更改StudentRec时，update类会有一个StudentRec方法（无参数）。

确切的详细信息留给提问者练习，因为这似乎是一项学校任务。

无法调用正确的数据

2 个答案: