How to sort different data type vales of the same arraylist?

I have an arraylist that has integers and string i want to sort the values when requested.

Example: if the user selected t from menu it would sort the student IDs or if the user selects f it would sort the students first names etc.

This is what I have so far, stuID method doesn't work when it is called. How can I fixed this and how do I sort the first names when method is called?

public class Student implements Comparable <Student>{        private int idNum;      private String fName;      private String surname;      private int entryYear;                  public int getIdNum() {          return idNum;      }      public void setIdNum(int idNum) {          this.idNum = idNum;      }      public String getfName() {          return fName;      }      public void setfName(String fName) {          this.fName = fName;      }      public String getSurname() {          return surname;      }      public void setSurname(String surname) {          this.surname = surname;      }      public int getEntryYear() {          return entryYear;      }      public void setEntryYear(int entryYear) {          this.entryYear = entryYear;      }                  public Student(int idNum, String fName, String surname, int entryYear) {          super();          this.idNum = idNum;          this.fName = fName;          this.surname = surname;          this.entryYear = entryYear;      }      public Student(int idNum) {          super();          this.idNum = idNum;      }      @Override      public String toString() {          return "Student [idNum=" + idNum + ", fName=" + fName + ", surname=" + surname + ", entryYear=" + entryYear                  + "]";      }              @Override      public int compareTo(Student s) {          if(this.getIdNum() > s.getIdNum())//               return 1;          else              return -1;      }        //  public int compare(Student fn) {   //      if(this.getfName().equals(fn.getfName()))//list all first names stored  //          return 1;  //      else  //          return -1;  //  }  }    

import java.util.ArrayList;  import java.util.Collections;  import java.util.Scanner;       public class StudentTest {  static ArrayList<Student> stu = new ArrayList<Student>();            public static void main(String[] args) {      Scanner sc= new Scanner(System.in);      char opt= ' ';      char menu= ' ';          Student s1= new Student(3, "Alice", "Zen", 1999);          Student s2= new Student(1, "John", "son", 1998);          Student s3= new Student(4, "Gin", "mora", 2000);          Student s4= new Student(1, "ola", "deed", 2001);          Student s5= new Student(5, "Marcus", "seph", 2004);          Student s6= new Student(6, "Gary", "moore", 1996);                          stu.add(s1);      stu.add(s2);      stu.add(s3);      stu.add(s4);      stu.add(s5);      stu.add(s6);                        //menu          System.out.println("Choose \nN- New student" + "\nT- Sort student ID" + "\nF- Sort student first name" + "\nL- Sort student last name"+ "\nE- Sort student entry year" +"\nX- Exit");       menu = sc.next().charAt(0);//main menu input(choice is Main Menu    //menu choices    while( menu == 'x') {       if ((menu == 'N') || (menu == 'n')) {           System.out.println("You chose Add!"+ "/nPlease enter new student information");       }       else if((menu == 'T')|| (menu == 't')) {           System.out.println("sort students ID numbers");           stuID();       }       else if((menu == 'F')|| (menu == 'f')) {           System.out.println("sort students first names");           //stuFn();       }       else if((menu == 'L')|| (menu == 'l')) {           System.out.println("sort students last name");       }       else if((menu == 'E')|| (menu == 'e')) {           System.out.println("sort students entry year");       }       else if((menu == 'X')|| (menu == 'x')) {           System.out.println("Good Bye!!");       }       else            System.out.println("Invalid option!!");  }          }                  public static void stuID() {      //sort id numbers listed      Collections.sort(stu);        for(Student st : stu) { //loop elements in array            System.out.println(st);// print elements in array    }  }  

https://stackoverflow.com/questions/66631502/how-to-sort-different-data-type-vales-of-the-same-arraylist March 15, 2021 at 10:05AM