主要
Scanner input = new Scanner(System.in);
System.out.print("Enter the name of the input file: ");
String fileName = input.next();
ClassRoll c = new ClassRoll();
c.display();
prompt();
System.out.print("Enter a command: ");
String ans = input.next();
while (!(ans.equalsIgnoreCase("q") || ans.equalsIgnoreCase("quit"))){
if(!(ans.equalsIgnoreCase("i") || ans.equalsIgnoreCase("insert") ||
ans.equalsIgnoreCase("a") || ans.equalsIgnoreCase("average") ||
ans.equalsIgnoreCase("n") || ans.equalsIgnoreCase("names") ||
ans.equalsIgnoreCase("r") || ans.equalsIgnoreCase("remove") ||
ans.equalsIgnoreCase("f") || ans.equalsIgnoreCase("find") ||
ans.equalsIgnoreCase("d") || ans.equalsIgnoreCase("display")))
{
System.out.println("Bad Command");
} else {
switch (ans.charAt(0)){
case 'i': c.insert();
break;
case 'a': c.sortAverage();
c.display();
break;
case 'n': c.sortLastNames();
c.display();
break;
case 'r': c.delete();
c.display();
break;
case 'f': Student s=c.find();
if (s == null) {
System.out.println("Student not found");
} else {
System.out.println(s.toString());
}
break;
case 'd': c.display();
break;
}
}
prompt();
System.out.print("Enter a command: ");
ans=input.next();
}
c.save();
System.out.println("Thank you!");
}
public static void prompt(){
System.out.println("Enter one of the following commands");
System.out.println("i or insert to insert a student in the class roll");
System.out.println("a or average to sort the students based on their average");
System.out.println("n or names to sort the students based on their last names");
System.out.println("r or remove to remove a student from the class roll");
System.out.println("f or find to find a student in the class roll");
System.out.println("d or display to display the class roll");
System.out.println("q or quit to exit the program");
}
CassRoll（）
ArrayList students = new ArrayList();
String title;
String fileName;
public ClassRoll(String f) throws IOException {
Scanner fileScan, lineScan;
String line;
fileName = f;
fileScan = new Scanner(new File(f));
title = fileScan.nextLine();
System.out.println("Title = " + title);
while (fileScan.hasNext()) {
line = fileScan.nextLine();
lineScan = new Scanner(line);
lineScan.useDelimiter("\t");
String lastName = lineScan.next();
String firstName = lineScan.next();
Student s = new Student(firstName, lastName);
s.setScore1(lineScan.nextInt());
s.setScore2(lineScan.nextInt());
s.setScore3(lineScan.nextInt());
students.add(s);
ClassRoll c;
c = new ClassRoll();
c.display();
}
}
void display() {
DecimalFormat fmt = new DecimalFormat("0.00");
System.out.println("\t\t\t" + title);
double classAverage = 0.0;
for (int i = 0; i < students.size(); i++) {
Student s = (Student) students.get(i);
System.out.print(s.toString());
System.out.println("\t" + fmt.format(s.getAverage()));
classAverage = classAverage + s.getAverage();
}
System.out.println("\t\t\t" + fmt.format(classAverage /
students.size()));
}
public void insert() {
Scanner input = new Scanner(System.in);
System.out.print("First Name: ");
String firstName = input.next();
System.out.print("Last Name: ");
String lastName = input.next();
System.out.print("Score 1: ");
int score1 = input.nextInt();
System.out.print("Score 2: ");
int score2 = input.nextInt();
System.out.print("Score 3: ");
int score3 = input.nextInt();
Student s = new Student(firstName, lastName);
s.setScore1(score1);
s.setScore2(score2);
s.setScore3(score3);
students.add(s);
}
private int search(String f, String l) {
int i = 0;
while (i < students.size()) {
Student s = (Student) students.get(i);
if (s.equals(f, l)) {
return i;
} else {
i++;
}
}
return -1;
}
public Student find() {
Scanner input = new Scanner(System.in);
System.out.print("First Name: ");
String firstName = input.next();
System.out.print("Last Name: ");
String lastName = input.next();
int i = search(firstName, lastName);
if (i >= 0) {
return (Student) students.get(i);
} else {
return null;
}
}
public void delete() {
Scanner input = new Scanner(System.in);
System.out.print("First Name: ");
String firstName = input.next();
System.out.print("Last Name: ");
String lastName = input.next();
int i = search(firstName, lastName);
if (i >= 0) {
students.remove(i);
} else {
System.out.println("Student not found");
}
}
public void sortLastNames() {
for (int i = 0; i < students.size() - 1; i++) {
for (int j = i + 1; j < students.size(); j++) {
Student s1 = (Student) students.get(i);
Student s2 = (Student) students.get(j);
if (s1.compareTo(s2) > 0) {
students.set(i, s2);
students.set(j, s1);
}
}
}
}
public void sortAverage() {
for (int i = 0; i < students.size() - 1; i++) {
for (int j = i + 1; j < students.size(); j++) {
Student s1 = (Student) students.get(i);
Student s2 = (Student) students.get(j);
if (s1.getAverage() < s2.getAverage()) {
students.set(i, s2);
students.set(j, s1);
}
}
}
}
public void save() throws IOException {
PrintWriter out = new PrintWriter(fileName);
out.println(title);
for (int i = 0; i < students.size(); i++) {
Student s = (Student) students.get(i);
out.println(s.toString());
}
out.close();
}
问题：
大家好！我对此程序有疑问，似乎无法解决。
这行代码在main和CassRoll（）上都引发了编译器错误
ClassRoll c =新的ClassRoll（）;
c.display（）;
错误是：
类ClassRoll中的构造函数ClassRoll不能应用于给定类型；
必需：字符串
找到：没有参数
原因：实际参数和形式参数列表的长度不同
最佳答案
ClassRoll中的构造函数定义为需要String参数：
公共ClassRoll（String f）
..但是您尝试创建ClassRoll的实例而不传递所需的String：
ClassRoll c =新的ClassRoll（）;
您应该能够通过将“ filename”字符串传递给构造函数来修复它，如下所示：
ClassRoll c =新的ClassRoll（文件名）;
希望这有道理并能有所帮助。