java - 学生类里面的平均方法不能应用于给定类型

Question

我在程序中收到上述错误。它在类(class)类中突出显示了以下代码行:

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

这是类(class)。之所以将括号删除，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;
}   

}
}

这是学生类:

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 ，我该如何解决该错误？

Answer 1

错误的答案是，假设在调用该方法之前已设置average()，test1和test2值，则删除test3方法的参数。也许您应该对其中的空值进行一些检查？

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

尽管在上述方法中返回 double可能更适用，如 @MarquisBlount所述:

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。使用当前代码，就永远不会为打印输出设置 avg2，因为您正在创建一个仅与方法范围相关的新变量: int avg2 = (( ...及其值一旦返回便被丢弃。

我建议进行以下更改:

将avg2从int更改为double

从average()

内部设置该类变量

可视化:

double avg2;

...

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

尽管您也可以在同一行中将 avg2实例化为零，但是您可以声明它，并使用 average()对其进行“更新”:

double avg2 = 0;

结果，在您的Course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;
}

再次，推断所有值都在每次调用之前填充。尽管看起来您已经按照这些假设构建了应用程序工作流。