I am trying to filter out specific elements of my array list but I keep getting an undeclared variable error.

public class Student
{
 
    private String name;
    private int age;
    private double gpa;
    
    public Student(String studentName, int studentAge, double studentGpa)
    {

       name = studentName;
       age = studentAge;
       gpa = studentGpa;
   
    }
   public String toString()
   {
   
       return "Student[Name: " + name + " Age: " + age + " GPA: " + gpa + "]n";
       
   }
   
}

The Students class is supposed to set up the array list and have multiple methods to determine which student has the highest GPA, the average GPA, etc…

import java.util.ArrayList;
import java.util.*;
import java.text.*;
import java.io.*;


public class Students 
{
    private ArrayList<Student> students;
    
    public Students()
    {
    
        students = new ArrayList<Student>();
        
    }
    
     
    
    public void readFile() throws IOException
    {
    String studentName;
    int studentAge;
    double studentGpa;
    String line;
    
       Scanner sc = new Scanner(new File("Students.txt"));
       
       while (sc.hasNextLine())
    {
    
        studentName = sc.nextLine();
        
        line = sc.nextLine();
        studentAge = Integer.parseInt(line);
        
        line = sc.nextLine();
        studentGpa = Double.parseDouble(line);
        
        Student student = new Student(studentName, studentAge, studentGpa);  
        students.add(student);
    }
    sc.close();
    }
    
    
    public String toString()
    {
        String results = "Students [";
        
        
        for(int i = 0; i < students.size(); i++)
            {results += students.get(i).toString();  }
            
           return results;
                 
    }

//this method keeps saying studentGpa is an undeclared variable

    public double highestGpa()
    {
    
        double highestGpa = students.get(0).studentGpa;
        
        for(int i = 0; i < students.size(); i++)
            
            if( students.get(i).studentGpa > highestGpa)
                highestGpa = students.get(i).studentGpa;
        
        
        
    
    }
    
}

The trouble I’m having is in the highestGpa() method. I am trying to access the studentGpa element inside of the array list but it keeps saying studentGpa is an undeclared method.

I tried changing studentGpa to gpa since I decided to create the Student constructor without using the ‘this’ keyword but since it was a private variable it wont work.

How should I go about accessing these different elements in the array list inside of separate methods?