Question

我想循环播放我的＆＃34; print_average_grade＆＃34;方法并打印ArrayList中所有学生的AVG等级。我尝试了一个＆＃34; for循环＆＃34;在主要的＆＃34;花名册＆＃34; class并获得一个错误陈述＆＃34;类型Roster中的方法print_average_grade（String）不适用于参数（Student）＆＃34;。

我的代码;

学生班：

public class Student {

private String StuID;
private String FName;
private String LName;
private String Email;
private int Age;
private double Grade1;
private double Grade2;
private double Grade3;


public Student (String stuid, String fname, String lname, String email,
    int age, double grade1, double grade2, double grade3)
{
this.StuID = stuid;
this.FName  =fname;
this.LName = lname;
this.Email = email;
this.Age = age;
this.Grade1 = grade1;
this.Grade2 = grade2;
this.Grade3 = grade3;

}
public String getStuID(){
    return this.StuID;}

public String getFName(){
return this.FName;}

public String getLName(){
return this.LName;}

public String getEmail(){
return this.Email;}

public int getAge(){
return this.Age;}

public double getGrade1(){
return this.Grade1;}

public double getGrade2(){
return this.Grade2;}

public double getGrade3(){
return this.Grade3;}

public String setStuID(String newStuID){
    return (this.StuID= newStuID);}

public String setFName(String newFName){
    return (this.FName= newFName);}

public String setLName(String newLName){
    return (this.LName= newLName);}

public String setEmail(String newEmail){
    return (this.Email= newEmail);}

public int setAge(int newAge){
    return (this.Age= newAge);}

public double setGrade1(double newGrade1){
    return (this.Grade1= newGrade1);}

public double setGrade2(double newGrade2){
    return (this.Grade2= newGrade2);}

public double setGrade3(double newGrade3){
    return (this.Grade1= newGrade3);}


 public String toString() {
    return String.format("StuID: %s\t First Name: %s\t Last Name: %s\t E-Mail: %s\t Age: %s\t Grade1: %s\t Grade2: %s\t Grade3: %s\t", this.StuID, this.FName, this.LName, this.Email,
            this.Age, this.Grade1, this.Grade2, this.Grade3);

}
}

名册等级：

import java.util.ArrayList;

public class Roster {
static ArrayList<Student> studentArray;

public Roster(ArrayList<Student> ar)
{
    studentArray=ar;
}
//3.A - Remove student.
public static void remove(String sdId){
    Student stud = null;
    for(Student s : studentArray){
        if(s.getStuID().equals(sdId))
            stud = s;}

    if(stud != null)
        studentArray.remove(stud);
    else
        System.out.println("ID does not exist."); 
}

//3.B - Print All Student Info
public static void print_all(){
    System.out.println("");{
    for (Student t: studentArray) {
        System.out.printf("%s\n",t);}}

}

//3.C - Print Average Grade
public static void print_average_grade(String studentID){
    for (Student v : studentArray){
        if(v.getStuID().equals(studentID)) {
            double total = v.getGrade1() + v.getGrade2() + v.getGrade3();
            double average = total / 3;
            System.out.println("Student ID#" + studentID + " Grade AVG= " + average);
        }
    }
 }

 //3.D - Print invalid E-mails
 public static void print_invalid_emails(){
    for(Student u : studentArray){
        if(u.getEmail().contains("@") && u.getEmail().contains(".") && !u.getEmail().contains(" ")){
            continue;}
        else{
            System.out.println(u.getEmail());}
        }   
    }   
 public static void main(String[]args){

    ArrayList<Student> studentArray = new ArrayList<Student>();

    studentArray.add(new Student("1","John","Smith","John1989@gmail.com", 20, 88, 79, 59));
    studentArray.add(new Student("2","Susan","Erickson","Erickson_1990@gmailcom", 19, 91, 72, 85));
    studentArray.add(new Student("3","Jack","Napoli","The_lawyer99yahoo.com", 19, 85, 84, 87));
    studentArray.add(new Student("4","Erin","Black","Erin.black@comcast.net", 22, 91, 98, 82));
    studentArray.add(new Student("5","Captain","Planet","PowIsUrs@planet.net", 65, 99, 98, 97));

    //Step 2D; print() specific student data example.
    System.out.println("");
    for (Student a: studentArray) {
        System.out.println(a.getStuID());
        System.out.println(a.getFName());
        System.out.println(a.getLName());}

new Roster(studentArray);
    Roster.print_all();
    Roster.print_invalid_emails();

//Works fine for one student.
    Roster.print_average_grade("1");

/This loop produces the error.
    for (Student v : studentArray) {
        print_average_grade(v);
    }
    Roster.remove("3");
    Roster.remove("3");      
}
}

我正在参加在线Java课程，由于质量问题，材料已多次更改。如果不是这个网站的解释，我会迷路。谢谢..

Answer 1

你的变量＆＃39; v＆＃39;是Student，但您的方法参数是String.Change方法。

public static void print_average_grade(Student v){

            double total = v.getGrade1() + v.getGrade2() + v.getGrade3();
            double average = total / 3;
            System.out.println("Student ID#" + v.getStuID + " Grade AVG= " + average);


 }

Answer 2

您正在将学生对象传递给print_average_grade而不是ID。

将代码改为：

    for (Student v : studentArray) {
        print_average_grade(v.getStuID());
    }

Answer 3

您的方法被定义为print_average_grade(String)您正在将Student对象传递给此方法，这正是您的编译器告诉您的内容。

您可以通过重载String一个来创建print_average_grade(Student student)。这可能如下所示。

public static void print_average_grade(Student student) {
    print_average_grade(student.getStuID());
}

或者您将循环更改为以下内容，以适合您存在的签名 print_average_grade方法。

for (Student v : studentArray) {
    print_average_grade(v.getStuID());
}

Answer 4

  for (Student v : studentArray) {
        print_average_grade(v);

您正在将Student传递给public static void print_average_grade(String studentID)，但它需要String参数。

使用print_average_grade(v.getStuID());

Answer 5

print_average_grade接受String的参数。但是，在调用方法时，您传递的是Student类型的对象。您所要做的就是在调用方法时传递studentId。

喜欢：

for(Student v : studentArray){
    print_average_grade(v.studentId);
}

这应该可以解决你的问题:)

循环我的ArrayList为所有学生打印AVG等级

5 个答案: