链接到我用于I / O的学生记录的Marks.txt文件： enter link description here
我有一个学生类（包含1个int studentID和6个赋值浮点数），它应该填充另一个名为 CourseSection 的类（只是一个ArrayList of学生对象），它是一个ArrayList，带有学生对象。
因此，在从Marks.txt文件中读取数据后，每个学生对象都应该填充名为 CourseSection 的ArrayList。
我正在尝试编写search（）方法，因此它会提示用户输入StudentID，然后这个int ID用于遍历Student对象的ArrayList，直到它.getID（）== ID（一个用户输入）。那么，它需要显示相应的学生6分配分数（浮点数）。我得到了一个
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Can only iterate over an array or an instance of java.lang.Iterable
错误来自于for循环之后的“course2”。 java不是作为ArrayList读取这个吗？它应该是Student对象的ArrayList正确吗？因为你可以看到我首先创建名为“course2”的CourseSection对象，然后我从文件Marks.txt中读取并指定“course2”来等于这个CourseSection.loadFrom方法（该方法返回一个CourseSection对象）。
public static void search(){
BufferedReader aFile;
CourseSection course2 = new CourseSection(); //creates course object which is ArrayList of Student objects
aFile = new BufferedReader( new FileReader("marks_test_no_empty_strings.txt"));
course2 = CourseSection.loadFrom(aFile); // reads .txt into course ArrayList
Scanner scanner = new Scanner(System.in);
int id;
boolean foundStudent = true;
System.out.print("Enter the Student's ID: ");
id = enterID();
for(Student s : course2) {
if(s.getID() == id) {
s.getA1();
s.getA2();
s.getA3();
s.getA4();
s.getMidterm();
s.getFinalExam();
}
else
System.out.println("ID not found!!!");
}
}
和 CourseSection 类如果有帮助：
import java.util.ArrayList;
import java.util.Iterator;
import java.io.*;
public class CourseSection {
private String name;
private ArrayList<Student> students;
/**
* Initializes the ArrayList<Student>.
*/
public CourseSection(String n)
{
name = n;
students = new ArrayList<Student>();
}
public CourseSection()
{
students = new ArrayList<Student>();
}
/**
* Will add a new student to the ArrayList.
* @param s A Student object.
*/
public void addStudent(Student s){
students.add(s);
}
/**
* Removes the selected student from the ArrayList.
* @param s A Student object.
*/
public void removeStudent(Student s){
Iterator studentIterator = students.iterator();
while(studentIterator.hasNext()){
if(studentIterator.next() == s)
studentIterator.remove();
}
}
/**
* Lists all the information for each student in the course section.
*/
public void listStudents(){
for(Student s: students){
System.out.println(s);
}
}
/**
* Reads aFile except for the header and continuously creates new student objects
* for a new CourseSection.
* @param aFile File to read from.
* @return CourseSection New CourseSection read from aFile
*/
public static CourseSection loadFrom(BufferedReader aFile) throws IOException{
//String line = aFile.readLine();
CourseSection course = new CourseSection(aFile.readLine());
aFile.readLine(); // skips line
while (aFile.ready()) //read until no more available (i.e., not ready)
{
course.addStudent(Student.loadFromST(aFile)); //read & add the student
}
return course;
}
}
这是我用来测试学生类中的 loadFrom 方法，并在 CourseSection中测试 loadFrom 的文件类
import java.io.IOException;
import java.util.InputMismatchException;
import java.util.Iterator;
import java.util.Scanner;
public class loadTester {
private static void studentLoadTest() throws IOException {
BufferedReader file1;
Student student1; // student object
//String line;
file1 = new BufferedReader(new FileReader("marks_test_no_empty_strings.txt"));
file1.readLine(); // skips 1st line
file1.readLine(); // skips 2nd line
/*
while(file1.ready())
{
System.out.println(file1.readLine());
}
*/
/* while((line = aFile.readLine()) != null) {
System.out.println(line);
}
*/
student1 = Student.loadFromST(file1); // using String Split
System.out.println(student1); // This method individually parses it
//file1.close();
}
private static void courseLoadTest() throws IOException {
//String line;
//CourseSection course = new CourseSection();
BufferedReader aFile = new BufferedReader(new FileReader("marks_test_no_empty_strings.txt"));
CourseSection course = CourseSection.loadFrom(aFile);
// course.loadFrom(aFile);
course.listStudents(); // this outputs the STUDENT OBJECTS IN THE ARRAY LIST!
//course = CourseSection.loadFrom(aFile);
//aFile.close();
}
public static void search(){
BufferedReader aFile;
CourseSection course2 = new CourseSection(); //creates course object which is ArrayList of Student objects
aFile = new BufferedReader( new FileReader("marks_test_no_empty_strings.txt"));
course2 = CourseSection.loadFrom(aFile); // reads .txt into course ArrayList
Scanner scanner = new Scanner(System.in);
int id;
boolean foundStudent = true;
System.out.print("Enter the Student's ID: ");
id = enterID();
for(Student s : course2) {
if(s.getID() == id) {
s.getA1();
s.getA2();
s.getA3();
s.getA4();
s.getMidterm();
s.getFinalExam();
}
else
System.out.println("ID not found!!!");
}
}
public static int enterID(){
Scanner scanner = new Scanner(System.in);
int id = 0;
try{
System.out.print("Enter the student's ID: ");
id = scanner.nextInt();
}catch(InputMismatchException e){
System.out.println("Error: InputMismatchException");
id = enterID();
}
return id;
}
public static void main(String[] args) throws IOException
{
System.out.println("Testing Student Object I/O Stream:");
studentLoadTest(); // testing to see if it outputs 1 Student Object per line
System.out.println();
System.out.println("Testing CourseSection creating ArrayList of Student Objects I/O Stream:");
courseLoadTest(); // this should output the Entire marks.txt file as an ArrayList of Student objects
search();
}
}
答案 0 :(得分：0)
course2不可迭代（CourseSection不实现Iterable）。
要迭代course2的学生，请在CourseSection课程中添加一个getter：
public List<Student> getStudents() {
return this.students;
}
并用
迭代它for(Student s : course2.getStudents()) {
}
答案 1 :(得分：0)
问题是CourseSection类不可迭代或数组。如果你做了这个改变，你可以像这样使用它：
public class CourseSection implements Iterable<Student> {
//adding the following method:
@Override
public Iterator<Student> iterator() {
return this.students.iterator();
}
您还可以通过更改主叫代码直接在学生身上进行迭代：
//You must add the getStudents() getter in CourseSection
for(Student s : course2.getStudents()) {
}
答案 2 :(得分：0)
CourseSection类不是一个数组或列表，它不会像这样编译
CourseSection类：
import java.util.ArrayList;
import java.util.Iterator;
import java.io.*;
import java.util.Scanner;
public class CourseSection {
private String name;
private ArrayList<Student> students;
/**
* Initializes the ArrayList<Student>.
*/
public CourseSection(String n)
{
name = n;
students = new ArrayList<Student>();
}
public CourseSection()
{
students = new ArrayList<Student>();
}
/**
* Will add a new student to the ArrayList.
* @param s A Student object.
*/
public void addStudent(Student s){
students.add(s);
}
/**
* Removes the selected student from the ArrayList.
* @param s A Student object.
*/
public void removeStudent(Student s){
Iterator studentIterator = students.iterator();
while(studentIterator.hasNext()){
if(studentIterator.next() == s)
studentIterator.remove();
}
}
/**
* Lists all the information for each student in the course section.
*/
public void listStudents(){
for(Student s: students){
System.out.println(s);
}
}
public ArrayList<Student> getStudents()
{
return students;
}
/**
* Reads aFile except for the header and continuously creates new student objects
* for a new CourseSection.
* @param aFile File to read from.
* @return CourseSection New CourseSection read from aFile
*/
public static CourseSection loadFrom(BufferedReader aFile) throws IOException{
//String line = aFile.readLine();
CourseSection course = new CourseSection(aFile.readLine());
aFile.readLine(); // skips line
while (aFile.ready()) //read until no more available (i.e., not ready)
{
course.addStudent(Student.loadFromST(aFile)); //read & add the student
}
return course;
}
}
搜索方法：
public static void search(){
BufferedReader aFile;
CourseSection course2 = new CourseSection(); //creates course object which is ArrayList of Student objects
aFile = new BufferedReader( new FileReader("marks_test_no_empty_strings.txt"));
course2 = CourseSection.loadFrom(aFile); // reads .txt into course ArrayList
Scanner scanner = new Scanner(System.in);
int id;
boolean foundStudent = true;
System.out.print("Enter the Student's ID: ");
id = enterID();
for(Student s : course2.getStudents()) {
if(s.getID() == id) {
s.getA1();
s.getA2();
s.getA3();
s.getA4();
s.getMidterm();
s.getFinalExam();
}
else
System.out.println("ID not found!!!");
}
}
学生班
public class Student {
private int ID;
private float a1;
private float a2;
private float a3;
private float a4;
private float midterm;
private float finalExam;
/**
* The Default constructor is used to intialize all instance variables
* in the class to zero.
*/
Student(){
ID = 0;
a1 = 0.0f;
a2 = 0.0f;
a3 = 0.0f;
a4 = 0.0f;
midterm = 0.0f;
finalExam = 0.0f;
}
Student(int id, float a1, float a2, float a3, float a4, float midterm, float finalExam) {
ID = id;
this.a1 = a1;
this.a2 = a2;
this.a3 = a3;
this.a4 = a4;
this.midterm = midterm;
this.finalExam = finalExam;
}
//Set methods for all instance variables of Student
public void setID(int newID)
{
ID = newID;
}
public void setA1(float newA1)
{
a1 = newA1;
}
public void setA2(float newA2)
{
a2 = newA2;
}
public void setA3(float newA3)
{
a3 = newA3;
}
public void setA4(float newA4)
{
a4 = newA4;
}
public void setMidterm(float newMidterm) // Typo was here for Mideterm
{
midterm = newMidterm;
}
public void setFinalGrade(float newFinal)
{
finalExam = newFinal;
}
//Get methods for instance variables of Student
public int getID()
{
return ID;
}
public float getA1()
{
return a1;
}
public float getA2()
{
return a2;
}
public float getA3()
{
return a3;
}
public float getA4()
{
return a4;
}
public float getMidterm()
{
return midterm;
}
public float getFinalExam()
{
return finalExam;
}
/**
* Prints all instance variables as a string.
* @return A string representing the student.
*/
public String toString(){
return(ID + ": " + a1 + " " + a2 + " " + a3 + " " + a4 + " " + midterm + " " + finalExam);
}
/**
* Will read from the linked file which will create and return a new Student object.
* @param aFile File to read from.
* @return A new Student object read from a line of the file.
* @throws IOException
* @throws NumberFormatException
*/
//using StringTokenizer
public static Student loadFromST(BufferedReader aFile) throws IOException {
Student newStudent = new Student();
//int i = 0;
//String zero = "0";
StringTokenizer st = new StringTokenizer(aFile.readLine()," ");
//while(st.hasMoreTokens()) {
//if(st.nextToken().isEmpty())
//zero = st.nextToken();
//else {
newStudent.ID = Integer.parseInt(st.nextToken());
newStudent.a1 = Float.parseFloat(st.nextToken());
newStudent.a2 = Float.parseFloat(st.nextToken());
newStudent.a3 = Float.parseFloat(st.nextToken());
newStudent.a4 = Float.parseFloat(st.nextToken());
newStudent.midterm = Float.parseFloat(st.nextToken());
newStudent.finalExam = Float.parseFloat(st.nextToken());
//i++;
//}
// }
return (newStudent);
}
//using Split String
/*
public static Student loadFromSS(BufferedReader aFile) throws java.io.IOException {
Student newStudent = new Student();
String[] words = aFile.readLine().split(" "); // can't split for anything bigger than 1 space
//for(int i = 0; i <= words.length; i++) {
// if(words[i].isEmpty())
// words[i] = "0";
// }
newStudent.ID = Integer.parseInt(words[0]);
newStudent.a1 = Float.parseFloat(words[1]);
newStudent.a2 = Float.parseFloat(words[2]);
newStudent.a3 = Float.parseFloat(words[3]);
newStudent.a4 = Float.parseFloat(words[4]);
newStudent.midterm = Float.parseFloat(words[5]);
newStudent.finalExam = Float.parseFloat(words[6]);
return newStudent;
}*/
}