Okay so I am building a program that will sort grades and records of students. It is a command-line program and when run it will start by asking for user input. there are several commands such as exit(exits program), load [file name](loads a file name), student [student name] (loads student records), etc. the others are not important. Well basically what I am wondering and what I am stuck on is all those functions will be in separate classes and will be called when the user inputs a specific command, but if I put the "load" command in its own class, then how do I get it to share its information with the other classes? I know I have to use BufferReader to read in the files, but how would I go implementing my load class, or if there is a better way feel free to say so. here is my code so far. there isn't much on my other classes because I feel like I need to figure out how to read in and share the file with the other classes first.
import java.util.*;
import java.io.*;
public class program7
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.println("Grade Stats by ");
System.out.print(">");
while(scan.hasNextLine())
{
String input = scan.nextLine();
if(input.equals("exit"))
{
System.exit(0);
}
else if(input.equals("help"))
{
System.out.println("exit - program closes.");
System.out.println("load [filename] - loads a class database specified in [filename].");
System.out.println("students - prints out a list of students from the class, along ");
System.out.println(" with total points, and final grades for each student.");
System.out.println("assignments - prints out a list of assignments from the file, along with points possible");
System.out.println("student [student name] - Prints report for the student");
System.out.print(">");
}
else if(input.contains("load"))
{
String[] split = input.split(" ");
LoadStudents loadStudents = new LoadStudents(split[1]);
loadStudents.getFromFile();
System.out.print(">");
}
else if(input.equals("students"))
{
Students students = new Students();
students.printer();
System.out.print(">");
}
else if(input.equals("assignments"))
{
System.out.print(">");
}
else if(input.contains("student"))
{
String[] split = input.split(" ");
Student student = new Student(split[1]);
System.out.print(">");
}
else if(input.contains("assignment"))
{
}
else if(input.equals("grades"))
{
}
else
{
System.out.println("exit - program closes.");
System.out.println("load [filename] - loads a class database specified in [filename].");
System.out.println("students - prints out a list of students from the class, along ");
System.out.println(" with total points, and final grades for each student.");
System.out.println("assignments - prints out a list of assignments from the file, along with points possible");
System.out.println("student [student name] - Prints report for the student");
System.out.print(">");
}
}
}
}
That is my main class, but here is my Load and Students class.
import java.util.*;
import java.io.*;
public class LoadStudents
{
public String inputFile;
public List<Object> info = new ArrayList<Object>();
public LoadStudents(String inputFile)
{
this.inputFile = inputFile;
}
public List<Object> getFromFile()
{
try
{
BufferedReader in = new BufferedReader(new FileReader(inputFile));
try
{
String line = "";
while(in.readLine() != null)
{
line = in.readLine();
info.add(line);
}
}
catch(IOException e)
{
System.err.println("Exception, man");
}
finally
{
in.close();
}
}
catch(FileNotFoundException e)
{
System.err.println("File wasnt found ");
}
catch(IOException e)
{
System.err.println("Exception, man");
}
return info;
}
}
import java.util.*;
public class Students
{
public Students()
{
}
public void printer()
{
List<Object> info = (new LoadStudents()).getFromFile();
for (int x = 0; x<info.size(); x++)
{
System.out.println(info.get(x));
}
}
}
the Students class isnt finished but I am trying to figure out how to read the list from other classes. I have done research and have seen 3 similar problems, but they there is still something I'm missing because I keep getting the error
.\Students.java:11: error: constructor Load in class Load cannot be applied to g
iven types;
List<Object> info = (new LoadStudents()).getFromFile();
^
required: String
found: no arguments
reason: actual and formal argument lists differ in length
1 error
I understand it wants input, but I want it to use the previous input the user gives it when he inputs the command "input [whateverfile]". Can anyone tell me how I can call that list my Load class produces to any other class?
There are many ways to do this. My suggestion is that your Load class should be a factory that actually creates a list of Student from the file, and not a list of strings.
Here are more suggestions:
Load class could have all methods statics and it could be non-instantiable. The fields you have in this class are useless after the file is read, you can just pass them to the static method as parameters.Load is not a nice name for that class. LoadStudents is more meaningful, or even better StudentFactory.Load and Student probably don't need to be public, package-private are be enough. Same for all the methods in these classes. Always use the lowest visibility possible.data() is not a nice name for that method either. Something like getStudents(), or if you follow above advice, getFromFile(), is more meaningful.EDIT: since you still don't understand what I mean, here's an example:
class StudentFactory {
private static List<Student> listCache = new ArrayList<>();
static List<Student> getStudents(final String filePath) {
if (listCache.isEmpty() {
BufferedReader in = null;
try {
in = new BufferedReader(new FileReader(filePath));
String line;
while((line = in.readLine()) != null) {
// Parse the line and create a Student instance from it, then add it to the list
listCache.add(student);
}
} catch(IOException e) {
System.err.println("Exception, man");
e.printStackTrace();
} catch(FileNotFoundException e) {
System.err.println("File wasnt found ");
e.printStackTrace();
} finally {
if (in != null) in.close();
}
}
return listCache;
}
private StudentFactory() {
// Avoid instantiation
}
}
Then you can just do
final List<Student> listOfStudents = StudentFactory.getStudents(filePath);
from anywhere in your code to get a list of students. filePath can be null if you already passed it previously.