Really confused on how to access just the age of a specific student where all the information of students have been stored in a textfile. I am reading the textfile and storing that info into a student object, just need help on accessing this.

public class Student {
    private String lName;
    private int idNumber;
    private int age;

    public Student() {
        lName = "";
        idNumber = 0;
        age = 0;
    }
    public Student(String l, int i, int a) {
        lName = l;
        idNumber = i;
        age = a;
    }

    public void setName(String last) {
        lName = last;
    }

    public String getName() {
        return lName;
    }

    public void setIdNum(int num) {
        idNumber = num;
    }

    public int getIdNum() {
        return idNumber;
    }

    public void setAge(int a) {
        age = a;
    }

    public int getAge() {
        return age;
    }
}

My Text File looks something like this: This info is stored in parallel array lists. I don't quite get how to implement this into an object to pass it into my second contractor method.

  Josh          2134         19
  Smith         5256         21
  Rogers        9248         19
  Andrew        7742         20

Here's what I've tried;

public static void main(String[] args) {
    String file = "studentData.txt";
    Scanner reader = new Scanner(file);

    ArrayList<Student> users = readFile(file);
    Student s = new Student();
    users.add(s);


    Scanner input = new Scanner(System.in);
    //user enters idNumber to display age
    System.out.println("Enter ID Number"); //exception handling to be added
    int idNum = input.nextInt();

//this part is where I'm stuck 
    for(int i = 0; i < users.get(i) i  ){
    if(idNum == users.get(i)){
     users.setAge(i);
}
}
     System.out.println(users.getAge());

}

//METHOD FOR READING FILE
 public static ArrayList<Student> readFile(String file)throws IOException{
    Scanner reader = new Scanner(new File(file));

    ArrayList<Student> list = new ArrayList<Student>();//creates ArrayList with student object

    reader.nextLine();//skips first line
    while(reader.hasNext()){//splits all text in the file into words
      String lName = reader.next();
      int idNum = reader.nextInt();
      int age = reader.nextInt();
      
    Student users = new Student(lName ,idNum, age); 
     list.add(users);
    }
    
   return list;

}//end method

The only way I think of fixing this is to read the file 3 times to store the names, idnum, and ages in seperate arraylists. And then use that separate array list to store the age using ageList.get(i). I beleive that would be super uneccessary??

CodePudding user response：

You can chain methods together like this.

      for(int i = 0; i < users.size(); i  ){
         if(idNum == users.get(i).getIdNum()){
            final Student temp = users.get(i);
            System.out.println("Student with an ID of "   temp.getIdNum()   " has an age of "   temp.getAge());
         }
      }

Here, I chained users.get(i) to get the Student at index i, then I call getIdNum(), which fetches the ID from that Student that I just fetched.

Then, I perform a == comparison --> Is the ID that the user entered the same as the ID from this particular Student I am looking at?

If the result is true, then I call users.get(i) again, which fetches that same Student again, and then I store that into a temporary Student variable called temp. temp is now referencing that Student on the ArrayList that passed the ID check.

Then, I take temp, and use the getIdNum() and getAge() methods that it has (because temp is an instance of Student, and Student has those methods), and use them to create a message that I print onto the command line.

Here is a complete, runnable example.

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;

public class SOQ_20220514
{

   public static class Student {
      private String lName;
      private int idNumber;
      private int age;
   
      public Student() {
         lName = "";
         idNumber = 0;
         age = 0;
      }
      public Student(String l, int i, int a) {
         lName = l;
         idNumber = i;
         age = a;
      }
   
      public void setName(String last) {
         lName = last;
      }
   
      public String getName() {
         return lName;
      }
   
      public void setIdNum(int num) {
         idNumber = num;
      }
   
      public int getIdNum() {
         return idNumber;
      }
   
      public void setAge(int a) {
         age = a;
      }
   
      public int getAge() {
         return age;
      }
   }

   public static void main(String[] args) throws IOException {
      String file = "studentData.txt";
      Scanner reader = new Scanner(file);
   
      ArrayList<Student> users = readFile(file);
      Student s = new Student();
      users.add(s);
   
   
      Scanner input = new Scanner(System.in);
    //user enters idNumber to display age
      System.out.println("Enter ID Number"); //exception handling to be added
      int idNum = input.nextInt();
   
   //this part is where I'm stuck 
      for(int i = 0; i < users.size(); i  ){
         if(idNum == users.get(i).getIdNum()){
            final Student temp = users.get(i);
            System.out.println("Student with an ID of "   temp.getIdNum()   " has an age of "   temp.getAge());
         }
      }
   
   }
//METHOD FOR READING FILE
   public static ArrayList<Student> readFile(String file)throws IOException{
      Scanner reader = new Scanner(new File(file));
   
      ArrayList<Student> list = new ArrayList<Student>();//creates ArrayList with student object
   
      reader.nextLine();//skips first line
      while(reader.hasNext()){//splits all text in the file into words
         String lName = reader.next();
         int idNum = reader.nextInt();
         int age = reader.nextInt();
      
         Student users = new Student(lName ,idNum, age); 
         list.add(users);
      }
    
      return list;
   
   }//end method

}