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错误：非静态方法不能从静态上下文中引用。（Another）“非静态方法不能从静态上下文中引用”问题
在我的情况下，该方法称为readFile（）。
嗨。我遇到了无数新手程序员之前遇到的同样的错误，但尽管几个小时一直阅读它，但我无法解决如何将这些知识应用于我的情况。
我认为代码可能需要重新编排，所以我包含了课程的全文。
我宁愿在main main类中放置main（）方法，但为了简单起见，它将它放在同一个类中。无论我把它放在哪里，我都会得到同样的错误。可以很容易地将readFile（）方法放在main（）方法中，但我更愿意学习如何创建像这样的小模块化方法并从main（）方法调用它们。 最初closeFile（）也是一个单独的方法。
程序应该：
- 打开.dat文件
- 从关于检查该文件中的数据读取结果
- 上的信息进行计算
- 输出的计算结果
该文件的每一行都是关于一个学生的信息。
一张包含三张试卷。
大部分计算都是针对个别学生的。
但是一些计算考虑了整个学生的集合（即他们的班级）。
注意：代码中使用“class”这个词，它指的是学生的学术类，而不是OO编程意义上的类。
我已经尝试过各种方法来解决问题。
当前的方法是收集与“考试”类相关的单个学生考试数据。
这对应于输入文件的单行，以及仅与该实例的其他属性有关的后续计算。
这些属性在readFile（）的while循环期间用值填充。
当while循环结束时，涉及整个考试集合（即整个学术课程）的三个计算被调用。
的第二个问题是：
在注释“声明属性”，我已经分离类的属性分为两个亚组：
那些我认为应该定义为类变量（用关键字static）。
那些我认为应该定义为实例变量。
你能指导我是否应该将关键字静态添加到第一组中的那些人。
一个相关的问题是：
应该将使用整个实例集合执行计算的方法声明为静态/类方法吗？
当我试图调用实例方法时，我得到了类似的错误。
谢谢。
PS：关于此论坛：
我已经用代码块包含了代码，但Java语法未突出显示。
也许在我提交帖子后它会改变。 但如果不是，我会很乐意重新格式化它，如果有人能告诉我如何。
PPS：这是一项家庭作业。
我已经创建了下面的所有代码。
“作业”标签已过时，所以我没有使用它。
输入文件名： “results.dat”
输入文件路径： “C：/用户/ ADMIN /桌面/ A1P3E1文件/ results.dat”
输入文件内容的（随机生成的数据）：
573,Kalia,Lindsay,2,8,10
966,Cheryl,Sellers,8,5,3
714,Shea,Wells,7,6,2
206,April,Mullins,8,2,1
240,Buffy,Padilla,3,5,2
709,Yoko,Noel,3,2,5
151,Armand,Morgan,10,9,2
199,Kristen,Workman,2,3,6
321,Iona,Maynard,10,2,8
031,Christen,Short,7,5,3
863,Cameron,Decker,6,4,4
986,Kieran,Harvey,7,6,3
768,Oliver,Rowland,8,9,1
273,Clare,Jacobs,9,2,7
556,Chaim,Sparks,4,9,4
651,Paloma,Hurley,9,3,9
212,Desiree,Hendrix,7,9,10
850,McKenzie,Neal,7,5,6
681,Myra,Ramirez,2,6,10
815,Basil,Bright,7,5,10
的Java文件名： “Exam.java”
Java包的名称： “a1p3e1”
Java项目名称： “A1P3E1”
项 的Java文件的内容：
/** TODO
* [+] Error Block - Add Finally statement
* [?] studentNumber - change data type to integer (or keep as string)
* [?] Change Scope of to Non-Instance Variables to Static (eg classExamGradeSum)
* [*] Solve "non-static method cannot be referenced from a static context" error
*
*/
package a1p3e1; // Assignment 1 - Part 3 - Exercise 1
import java.io.*;
import java.util.*;
/**
*
* @author
*/
public class Exam {
// (1) Declare Attributes
// (-) Class Attributes
protected Scanner fileIn;
protected Scanner lineIn;
private String line;
private String [] splitLine;
private String InFilePath = "C:/Users/ADMIN/Desktop/A1P3E1 Files/results.dat";
private int fileInRowCount = 20;
private int fileInColumnCount = 6;
private int fileOutRowCount = 20;
private int fileOutColumnCount = 14;
// private int classExamGradeSum = 0;
private int classExamGradeSum;
private double classExamGradeAverage = 0.0;
private int [] classExamGradeFrequency = new int [10];
protected Exam exam [] = new Exam [fileInRowCount];
// (-) Instance Attributes
private String studentNumber;
private String forename;
private String surname;
private int paper1Grade;
private int paper2Grade;
private int paper3Grade;
private String paper1Outcome;
private String paper2Outcome;
private String paper3Outcome;
private int fileInRowID;
private int failCount;
private int gradeAverageRounded;
private int gradeAverageQualified;
private String examOutcome;
// (3) toString Method Overridden
@Override
public String toString() {
return "\n Student Number: " + studentNumber
+ "\n Forename: " + forename
+ "\n Surname: " + surname
+ "\n Paper 1 Grade: " + paper1Grade
+ "\n Paper 2 Grade: " + paper2Grade
+ "\n Paper 3 Grade: " + paper3Grade
+ "\n Paper 1 Outcome: " + paper1Outcome
+ "\n Paper 2 Outcome: " + paper2Outcome
+ "\n Paper 3 Outcome: " + paper3Outcome
+ "\n File In Row ID: " + fileInRowID
+ "\n Fail Count: " + failCount
+ "\n Exam Grade Rounded: " + gradeAverageRounded
+ "\n Exam Grade Qualified: " + gradeAverageQualified
+ "\n Exam Outcome: " + examOutcome;
}
// (4) Accessor Methods
public String getStudentNumber() {
return studentNumber;
}
public String getForename() {
return forename;
}
public String getSurname() {
return surname;
}
public int getPaper1Grade() {
return paper1Grade;
}
public int getPaper2Grade() {
return paper2Grade;
}
public int getPaper3Grade() {
return paper3Grade;
}
public String getPaper1Outcome() {
return paper1Outcome;
}
public String getPaper2Outcome() {
return paper2Outcome;
}
public String getPaper3Outcome() {
return paper3Outcome;
}
public int getFileInRowID() {
return fileInRowID;
}
public int getFailCount() {
return failCount;
}
public int getGradeAverageRounded() {
return gradeAverageRounded;
}
public int getGradeAverageQualified() {
return gradeAverageQualified;
}
public String getExamOutcome() {
return examOutcome;
}
// (5) Mutator Methods
public void setStudentNumber (String studentNumber) {
this.studentNumber = studentNumber;
}
public void setForename (String forename) {
this.forename = forename;
}
public void setSurname (String surname) {
this.surname = surname;
}
public void setPaper1Grade (int paper1Grade) {
this.paper1Grade = paper1Grade;
}
public void setPaper2Grade (int paper2Grade) {
this.paper2Grade = paper2Grade;
}
public void setPaper3Grade (int paper3Grade) {
this.paper3Grade = paper3Grade;
}
public void setPaper1Outcome (String paper1Outcome) {
this.paper1Outcome = paper1Outcome;
}
public void setPaper2Outcome (String paper2Outcome) {
this.paper2Outcome = paper2Outcome;
}
public void setPaper3Outcome (String paper3Outcome) {
this.paper3Outcome = paper3Outcome;
}
public void setFileInRowID (int fileInRowID) {
this.fileInRowID = fileInRowID;
}
public void setFailCount (int failCount) {
this.failCount = failCount;
}
public void setGradeAverageRounded (int gradeAverageRounded) {
this.gradeAverageRounded = gradeAverageRounded;
}
public void setGradeAverageQualified (int gradeAverageQualified) {
this.gradeAverageQualified = gradeAverageQualified;
}
public void setExamOutcome (String examOutcome) {
this.examOutcome = examOutcome;
}
// (2) Constructor Methods
// (-) Constructor Method - No Arguments
public Exam() {
this.studentNumber = "";
this.forename = "";
this.surname = "";
this.paper1Grade = 0;
this.paper2Grade = 0;
this.paper3Grade = 0;
this.paper1Outcome = "";
this.paper2Outcome = "";
this.paper3Outcome = "";
this.fileInRowID = 0;
this.failCount = 0;
this.gradeAverageRounded = 0;
this.gradeAverageQualified = 0;
this.examOutcome = "";
}
// (-) Constructor Method - With Arguments (1)
public Exam (
String studentNumber,
String forename,
String surname,
int paper1Grade,
int paper2Grade,
int paper3Grade,
String paper1Outcome,
String paper2Outcome,
String paper3Outcome,
int fileInRowID,
int failCount,
int gradeAverageRounded,
int gradeAverageQualified,
String examOutcome) {
this.studentNumber = studentNumber;
this.forename = forename;
this.surname = surname;
this.paper1Grade = paper1Grade;
this.paper2Grade = paper2Grade;
this.paper3Grade = paper3Grade;
this.paper1Outcome = paper1Outcome;
this.paper2Outcome = paper2Outcome;
this.paper3Outcome = paper3Outcome;
this.fileInRowID = fileInRowID;
this.failCount = failCount;
this.gradeAverageRounded = gradeAverageRounded;
this.gradeAverageQualified = gradeAverageQualified;
this.examOutcome = examOutcome;
}
// (-) Constructor Method - With Arguments (2)
public Exam (
String studentNumber,
String forename,
String surname,
int paper1Grade,
int paper2Grade,
int paper3Grade) {
this.studentNumber = studentNumber;
this.forename = forename;
this.surname = surname;
this.paper1Grade = paper1Grade;
this.paper2Grade = paper2Grade;
this.paper3Grade = paper3Grade;
this.paper1Outcome = "";
this.paper2Outcome = "";
this.paper3Outcome = "";
this.fileInRowID = 0;
this.failCount = 0;
this.gradeAverageRounded = 0;
this.gradeAverageQualified = 0;
this.examOutcome = "";
}
// (6) Main Method
public static void main (String[] args) throws Exception {
Exam.readFile();
}
// (7) Other Methods
// (-) Read File Into Instances Of Exam Class
// limitation: hard coded to 6 column source file
public void readFile() throws Exception {
try {
fileIn = new Scanner(new BufferedReader(new FileReader(InFilePath)));
int i = 0;
while (fileIn.hasNextLine()) {
line = fileIn.nextLine();
splitLine = line.split (",", 6);
// create instances of exam from file data and calculated data
exam [i] = new Exam (
splitLine [0],
splitLine [1],
splitLine [2],
Integer.parseInt (splitLine [3]),
Integer.parseInt (splitLine [4]),
Integer.parseInt (splitLine [5]),
convertGradeToOutcome (paper1Grade),
convertGradeToOutcome (paper2Grade),
convertGradeToOutcome (paper3Grade),
i + 1,
failCount(),
gradeAverageRounded(),
gradeAverageQualified(),
convertGradeToOutcome (gradeAverageQualified));
fileIn.nextLine();
i ++;
}
classExamGradeFrequency();
classExamGradeSum();
classExamGradeAverage();
// close file
fileIn.close();
} catch (FileNotFoundException | NumberFormatException e) {
// fileIn.next();
System.err.println("Error: " + e.getMessage());
//System.out.println ("File Error - IO Exception");
}
for (Exam i : exam) {
System.out.println(i.toString());
System.out.println();
}
// System.out.println(classExamGradeSum);
// System.out.println();
System.out.println(classExamGradeAverage);
System.out.println();
System.out.println(classExamGradeFrequency);
System.out.println();
}
// (-) Fail Count (1 Student, 3 Papers)
public int failCount() {
//
if (paper1Grade > 6){
failCount = failCount + 1;
}
if (paper2Grade > 6){
failCount = failCount + 1;
}
if (paper3Grade > 6){
failCount = failCount + 1;
}
return failCount;
}
// (-) Grade Average Rounded (1 Student, 3 Papers)
public int gradeAverageRounded() {
gradeAverageRounded = (int) Math.ceil(
(paper1Grade + paper2Grade + paper3Grade)/3);
return gradeAverageRounded;
}
// (-) Grade Average Qualified (1 Student, 3 Papers)
public int gradeAverageQualified(){
gradeAverageQualified = gradeAverageRounded;
if (failCount >= 2 && gradeAverageRounded <= 6) {
gradeAverageQualified = 7;
}
return gradeAverageQualified;
}
// (-) Convert Grade to Outcome (Pass/Fail)
public String convertGradeToOutcome (int grade) {
String outcome;
if (grade <= 6){
outcome = "Pass";
} else if (grade > 6){
outcome = "Fail";
} else {
outcome = "Unknown (Error)";
}
return outcome;
}
// (-) Class Exam Grade Sum (All Students, All Papers)
/** assumption: average grade for class is average of grades awarded,
* using rounded figures, not raw per paper results
*/
public void classExamGradeSum() {
classExamGradeSum = 0;
// for each loop (to iterate through collection of exam instances)
for (Exam i : exam) {
classExamGradeSum = classExamGradeSum + i.gradeAverageQualified;
}
}
// (-) Class Exam Grade Average (All Students, All Papers)
/** assumption: average grade for class is average of grades awarded,
* using rounded figures, not raw per paper results
* assumption: <fileInRowCount> is correct
*/
public double classExamGradeAverage() {
classExamGradeAverage = classExamGradeSum/fileInRowCount;
return classExamGradeAverage;
}
// (-) Class Exam Grade Frequency (Count of Instances of Each Final Grade)
/** Example:
* frequency of average grade "5"
* is stored in array <classExamGradeFrequency [4]>
*/
public void classExamGradeFrequency() {
// for each loop (to iterate through collection of exam instances)
for (Exam i : exam) {
classExamGradeFrequency [i.getGradeAverageQualified() - 1] ++;
}
}
}// endof class
确定。但是（如果将整个文件放到上下文中）：1. _should_ {readFile（）}是一个实例方法吗？ 2. readFile创建{new Exam（）}的多个实例 – Default300 2013-02-10 16:11:51
第二次尝试回复！
好的。但是（如果将整个文件放到上下文中）：
1. _should_“readFile（）”是一个实例方法吗？
2。“readFile（）”创建“新Exam（）”的多个实例
PS：Re论坛，如何在此回复编辑器中格式化代码（例如，如果我按Enter键，它发布回复而不是插入换行符） – Default300 2013-02-10 16:20:31
@ Reimeus好吧，那么我是否应该有另一个类，它可以容纳Main（），readFile（）以及其他只需要，并且可能应该只有一个实例的其他变量和方法？ （刚刚在打字时看到你已经提出了这个建议。）PS在论坛中提供任何提示。 – Default300 2013-02-10 16:32:54