类中的方法平均值Student不能应用于给定的类型

Question

我的程序中出现了上述错误。它在课程类中突出显示了这一行代码：

return(s1.average((+1.average；

这是课程课。括号之所以被注释掉，是因为我的教练告诉我要这样做。

public class Course extends Student
{
private String course;
private Student s1, s2, s3, s4, s5;
private int studentcount = 1;
public Course (String name)
{
   super(); //
   course = name;
}
public Student addStudent(String first, String last, Address home, Address school)
{
//if (studentcount == 1){
  s1 = new Student(first,last,home,school);
  studentcount++;          
  return s1;
//}    
 //if (studentcount == 2) {
  s2 = new Student(first,last,home,school);
      studentcount++;
  return s2;
//}
//else if (studentcount == 3){
  s3 = new Student(first,last,home,school);
  studentcount++;
      return s3;
//}
// else if (studentcount == 4){
  s4 = new Student(first,last,home,school);
      studentcount++;
  return s4;
//}
//else if (studentcount == 5) {
  s5 = new Student(first,last,home,school);
      studentcount++;
   return s5;
 //}
//else {
System.out.println("No More students allowed in the class");
return null;
//}
}
public double average()
{
}
public String roll()
{
String results = "";
if (studentcount == 1){
  results += s1.toString () +"n";
  return results;
}    
 if (studentcount == 2) {
  results += s1.toString () +"n";
  results += s2.toString () +"n";
  return results;
}
else if (studentcount == 3){
  results += s1.toString () +"n";
  results += s2.toString () +"n";
  results += s3.toString () +"n";
  return results;
}
else if (studentcount == 4){
  results += s1.toString () +"n";
  results += s2.toString () +"n";
  results += s3.toString () +"n";
  results += s4.toString () +"n";
  return results;
}
else if (studentcount == 5) {
  results += s1.toString () +"n";
  results += s2.toString () +"n";
  results += s3.toString () +"n";
  results += s4.toString () +"n";
  results += s5.toString () +"n";
  return results;
    } 
    else{
  return null;
}   
}
}

这是学生班：

public class Student 
{
Address home = new Address("1027 Charleston St","Lincoln", "Ne", 68508);
Address school = new Address("1534 E St", "Lincoln", "Ne", 68508);
Student mike = new Student("Mike", "Vinci", home, school);
Student john = new Student("John", "Doe", home, school, 90, 80, 199);
//Below are the ints used
int test1 = 0;
int test2 = 0;
int test3 = 0;
int avg2;
int error = 0;
public Student(){
     //empty
}
public void setTestScore(int testNum, int score)
{
    if (testNum == 1)
        test1 = score;
    else if (testNum == 2)
        test2 = score;
    else if (testNum == 3)
        test3 = score;
}
public int getTestScore(int testNum)
{
    if (testNum == 1)
        return test1;
    else if (testNum == 2)
        return test2;
    else if (testNum == 3)
        return test3;
    else
         return error;
}
public double average(int test1, int test2, int test3)
{
    int avg2 = ((test1 + test2 + test3)/3); //finds the average of the tests
    return avg2;
}
private String firstName, lastName; //private ints for coding
private Address homeAddress, schoolAddress;
public Student (String first, String last, Address home, Address school) 
{
    firstName = first;
    lastName = last;
    homeAddress = home;
    schoolAddress = school;
}
public Student (String first, String last, Address home, Address school, int test11, int test22, int test33) 
{
    firstName = first;
    lastName = last;
    homeAddress = home;
    schoolAddress = school;
    test11 = test1;
    test22 = test2;
    test33 = test3;
}
public String toString() 
{
    String result;
    result = firstName + " " + lastName + "n";
    result += "Home Address:n" + homeAddress + "n";
    result += "School Address:n" + schoolAddress + "n";
    result += "Average=" + avg2 + " with Tests: " + test1 + ", " + test2 + ", " + test3;
    return result; //returns the result
}
class Address
{
private String streetAddress, city, state;
private long zipCode;
public Address(String street, String town, String st, long zip)
{
    streetAddress = street;
    city = town;
    state = st;
    zipCode = zip;
}
public String toString()
{
    String result;
    result = streetAddress + "n";
    result += city + "," + state + " " + zipCode;
    return result; //returns the result
}
} 
}

所以问题是我该如何修复这个错误

Answer 1

错误的答案是删除average()方法的参数，前提是test1、test2和test3值将在调用该方法之前设置。也许您应该检查其中的空值？

public int average()
{
    int avg2 = ((test1 + test2 + test3)/3); //finds the average of the tests
    return avg2;
}

尽管在上面的方法中返回double可能更适用，正如@MarquisBlount所提到的：

由于您将avg2声明为实例变量，因此可以使用average()更新它以供以后使用。对于当前的代码，avg2永远不会为打印输出设置，因为您正在创建一个仅与方法范围相关的新变量：int avg2 = (( ...，一旦返回，它的值就会被丢弃。

我建议进行以下更改：

• 将avg2从int更改为double
• 从average()中设置该类变量

可视化：

double avg2;
...
public int average()
{
    avg2 = ((test1 + test2 + test3)/3); //finds the average of the tests
    return avg2;
}

尽管您也可以在声明avg2的同一行中将其实例化为零，并使用average():简单地"更新"它

double avg2 = 0;

---

因此，在课程类的double average()方法中，您可以调用：

public double average()
{
    return (s1.average() + s2.average() + s3.average() + s4.average() + s5.average()) / 5.0;
}

同样，推断所有值都会在每次调用之前填充。尽管看起来您的应用程序工作流已经围绕这些假设构建好了。

Answer 2

而不是调用：

return (s1.average() + s1.average() + s1.average() + s1.average() + s1.average()) / 5.0

调用：

return (s1.average(s1.test1,s1.test2,s1.test3) + s2.average(s2.test1,s2.test2,s2.test3) + s3.average(s3.test1,s3.test2,s3.test3) + s4.average(s4.test1,s4.test2,s4.test3) + s5.average(s5.test1,s5.test2,s5.test3)) / 5.0