如何通过主 Class 从另一个 Class 调用方法？

Question

Apologies for the poor title but I don't know how to phrase my issue. I am attempting to call the getSSN method from the Student class in my BubbleSorter class after a few students have been placed in an ArrayList. How can I call for the specific SSN variable. I understand why the error is occuring, but not how to change it to make it work. The error message is as follows: The method getSSN() is undefined for the type SearchandSort.

My Student Class:

public class Student {

    private String firstName, lastName;
    private int SSN;

    public Student(String first, String last, int ssn) {

        firstName = first;
        lastName = last;
        SSN = ssn;
    }

    public String toString() {
        return lastName + ", " + firstName + " " + SSN + "\t";
    }

    public boolean equals(Object other) {

        return (lastName.equals(((Student)other).getLastName()) && firstName.equals(((Student)other).getFirstName()) && (SSN == (((Student)other).getSSN())));
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName (String lastName) {
        this.lastName = lastName;
    }

    public int getSSN() { 
        return SSN;
    }

    public void setSSN(int SSN) {
        this.SSN = SSN;
    }
}

My BubbleSorter:

import java.lang.reflect.Array;

// “On my honor, I have neither received nor given any unauthorized assistance on this examination.”
public class BubbleSorter {

    public static void bubbleSort(SortandSearch Students[]) {

        int lastPos;
        int index;
        int temp;

        for (lastPos = Students.length-1; lastPos >= 0; lastPos--) {
            for (index = 0; index <= lastPos - 1; index++) {

                if (((Students[index]).getSSN()) - ((Students[index+1].getSSN())) > 0) {
                    temp = Students[index].getSSN();
                    Students[index].getSSN() = Students[index+1].getSSN();
                    Students[index+1].getSSN() = temp;
                }
            }
        }
    }
}

My main class:

import java.util.ArrayList;
import java.util.Scanner;

public class SortandSearch {

    public static void main(String[] args) {

        Student a = new Student("Ryan", "Jones", 123456);
        Student b = new Student("Jolie", "Decker", 123457);

        ArrayList<Student> Students = new ArrayList<Student>();

        Students.add(a);
        Students.add(b);

        System.out.println(Students);
        bubbleSort(Students);
        System.out.println(Students);

        System.out.println("Please enter the SSN of the student you are searching for:");
        Scanner scan = new Scanner(System.in);
        int searchKey = scan.nextInt();

        for (int index = 0; index < Students.size(); index++) {
            if (Students.get(index).getSSN() == searchKey) {
                System.out.print("The student with SSN " + searchKey + " is located at " + index);
            }
        }
    }
}

EDIT:

The error now shows: The type of the expression must be an array type but it resolved to ArrayList.

New BubbleSorter:

import java.util.ArrayList;

// “On my honor, I have neither received nor given any unauthorized assistance on this examination.”
public class BubbleSorter {

    public static void bubbleSort(ArrayList<Student> studentList) {

        int lastPos;
        int index;
        int temp;

        for (lastPos = studentList.size()-1; lastPos >= 0; lastPos--) {
            for (index = 0; index <= lastPos - 1; index++) {

                if ((studentList.get(index).getSSN()) - ((studentList.get(index).getSSN())) > 0) {
                    temp = studentList[index];
                    studentList[index] = studentList[index+1];
                    studentList[index+1] = temp;
                }
            }
        }
    }
}

Answer 1

In SortandSearch you put instances of Student into ArrayList<>, and the your bubbleSort method must also take argument of this type or at least List and then convert it to array and return sorted list:

public static List<Student> bubbleSort(List<Student> studentsList) {
    Student[] Students = studentsList.toArray(new Student[studentsList.size()]);
// ...
    return Arrays.asList(Students);
}

And in the calling main method you need to store sorted list:

    List<Student> sorted = BubbleSorter.bubbleSort(Students);
    System.out.println(sorted);

Answer 2

There seem multiple things wrong to this code. I think you are trying unnessecary casting your arraylist to something else

First, I think your function signature should change to

 public static void bubbleSort(ArrayList<Student> studentList) 

And then you can access the elements with:

studentList.get(index).getSSN()