循環使用ArrayList爲所有學生打印AVG成績

我想遍歷我的「print_average_grade」方法，並打印ArrayList中所有學生的AVG成績。我已經在Main中爲「Roster」類嘗試了一個「for循環」，並且得到一個錯誤，指出「Roster類型中的方法print_average_grade（String）不適用於參數（Student）」。循環使用ArrayList爲所有學生打印AVG成績

我的代碼;

學生類別：

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); 

} 
}

名冊類：

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","[email protected]", 20, 88, 79, 59)); 
    studentArray.add(new Student("2","Susan","Erickson","[email protected]", 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","[email protected]", 22, 91, 98, 82)); 
    studentArray.add(new Student("5","Captain","Planet","[email protected]", 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");  
} 
}

我參加在線課程的Java和因爲質量的材料已經被多次更改。如果不是這個網站的解釋，我會迷路。謝謝..

來源

2015-11-10 ajbnetworkguy

通's.getStuID（）'的方法。 –

而且它也會更好地使用列表的等級。 – maraca

您正在將學生對象傳遞給print_average_grade而不是id。

Chnge代碼：

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

來源

2015-11-10 14:50:08 user2964536

你的方法，你print_average_grade(String)傳遞一個Student對象這種方法，只需that's你的編譯器告訴你的定義。

您可以簡單地通過重載字符串1來創建print_average_grade(Student student)。這可能如下所示。

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

或更改環路以下，以滿足您的existsing print_average_grade方法的簽名。

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

來源

2015-11-10 14:50:55 SomeJavaGuy

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

你傳遞一個Student到public static void print_average_grade(String studentID)但它需要一個String參數。

使用print_average_grade(v.getStuID());

來源

2015-11-10 14:51:02 Ramanlfc

你的變量「V」是一個學生，但你的方法參數是String.Change的方法。

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); 


}

來源

2015-11-10 14:53:03

print_average_grade接受字符串的參數。但是，在調用傳遞Student類型對象的方法時。您只需在調用方法時傳遞studentId。

像：

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

這應該解決您的問題:)

來源

2015-11-10 14:55:14

循環使用ArrayList爲所有學生打印AVG成績

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