input command and indexOf

[David Ausere]

Can you use an input command with the indexOf statement?  If so how would it look?  

[Ivan Pronin]

indexOf() method is applicable for any String object. E.g. int i = "my_string".indexOf("_");
i == 2;

Not clear, what do you mean by "input command"?

[David Ausere]

Here is my code which is obvious doo doo.

               int delid;
               System.out.println("Please input Student ID: ");
               delid = Integer.parseInt(input.nextLine());
               int removeID; 
               removeID = int.indexOf(delid);

My expected outcome is I input the student ID.  Then removeID is given the Index position of that input.

[Zahro Alfelpha]

I assume you're looking for something like this

List<Integer> studentsIds = Arrays.asList(new Integer[] {1000, 1001, 1002, 1003, 1004, 1005});

try {
    System.out.print("Please input Student ID: ");
    int removeID = studentsIds.indexOf(new Scanner(System.in).nextInt());
    
    if (removeID != -1) {
        System.out.println("removeID is " + removeID);
    } else {
        System.out.println("That student ID does not exist");
    }
    
} catch (InputMismatchException e) {
    System.out.println("Input must be a valid integer");
}

[David Ausere]

Tried that but it just returns a value of -1 every time.

[Norm Radder]

returns a value of -1 every time.  

Can you post the code and both the Strings used in the indexOf method so we can see what you are talking about?

[David Ausere]

Sure thing.

This is my updated code (Not working that I am throwing my hands up in the air with)

import java.util.*;

public class Roster {

public static void main(String[] args) 
    {
       ArrayList<Student> Roster = new ArrayList<>();
       Scanner input = new Scanner(System.in);

       int menuChoice = 4;
       
       do {
           System.out.println("\t\tStudent Roster Menu");
           System.out.println("\t\t1. Add Student");
           System.out.println("\t\t2. View Students");
           System.out.println("\t\t3. Delete Student");
           System.out.println("\t\t4. Exit");
           try {
               System.out.println("Enter a choice: ");
               menuChoice = Integer.parseInt(input.nextLine());
           } catch (NumberFormatException e) {
               continue;
           }
                      
           if (menuChoice==1)
           {                                                           
               int getNumRoster=Roster.size();
               int ID = getNumRoster + 1;
               System.out.println("Your Student ID is: " + ID);
               
               System.out.println("First name: ");
               String fname = input.nextLine();
               
               System.out.println("Last name: ");
               String lname = input.nextLine();
               
               System.out.println("Email: ");
               String email = input.nextLine();

               int age;
               System.out.println("Age: ");
               age = Integer.parseInt(input.nextLine());
               
               int grade1;
               System.out.println("Grade 1: ");
               grade1 = Integer.parseInt(input.nextLine());

               int grade2;
               System.out.println("Grade 2: ");
               grade2 = Integer.parseInt(input.nextLine());

               int grade3;
               System.out.println("Grade 3: ");
               grade3 = Integer.parseInt(input.nextLine());

               Student students = new Student (ID, fname, lname, email, age,
                                                grade1, grade2, grade3);
               Roster.add(students);
            
            } if (menuChoice==2) {
               System.out.println("Students: ");
               Roster.forEach((students) -> {
                   System.out.println(students);
                   System.out.println();
               });
                       
           }
           
            if (menuChoice==3) {
                
               Scanner inputScanner = new Scanner(System.in);
               System.out.println("Type student name for search:");
               String studentFName = inputScanner.nextLine();
               
               for (int i = 0; i < Roster.size(); i++)
               {
                   if (Roster.get(i).getFirstname().equals(studentFName));
                    System.out.println(Roster.get(i));                 
               }              
             
               System.out.println("Student Not Found");
               
                                               
            }                           
       } while (menuChoice<4);
    }
}

I have a menu Option 1,2,3,4

I can add a Student.  I can View and not I am on the deleting portion.

I tried this method

if (menuChoice==3) {
               
               int delid;
               System.out.println("Please input Student ID: ");
               delid = Integer.parseInt(input.nextLine());
               int getNumRoster=Roster.size();
               int ID = getNumRoster;
               
            if (delid <= ID && delid >= 1)   {
               System.out.println("Do you want to Delete Student ID #" 
                                    + delid + "?  Type YES" );
               String response =  input.nextLine();
               if (response.equals("YES")) {
                    Roster.remove(delid -1);
                    System.out.println("ID record Deleted");
                }
                else System.out.println("ID NOT DELETED.  YES not recognized");
            }
               else System.out.println("ID NOT RECOGNIZED!");                                
            }                         

But obviously there are some errors in my logic with this way.  So I was thinking..

Can I search the array for the Student ID and get the Array position for that ID and then delete that ID.  I tried and I failed miserably at attempt.

So then I am thinking can I search for the First and Last name get a match with the array position and then delete that one.  Which I am failing miserably at as well.

Need some guidance for sure.

[Norm Radder]

What are the Strings that you are using with the indexOf method?

Where is the indexOf method used in your code? I can't see where the statement is that you are having problems with.

[David Ausere]

Norm,

I had deleted that code out of frustration unfortunately.  But at the top of the screen you can see what I "tried".

[Norm Radder]

Sorry, there is a lot of confusion.  I don't see an indexOf in the first post.  I'd rather not guess.
Can you post the code, the Strings that were used and the error messages?

[David Ausere]

Norm,

All the code is there.  The whole program.  The indexOf is just one way I tried to accomplish my goal.  So I tried what Zephro suggested, but all I got was  return of -1 not the index.  

[Norm Radder]

Sorry, there is a lot of code on this thread.  I don't see where there is an indexOf method used in the program so I can't recommend how you change the code to use the method correctly.

accomplish my goal

Is this your goal:

search the array for the Student ID

Normal array searches are done with a loop through the elements in a array. An if test is used to look for desired elements.
If the array contains Student objects, what methods does the Student class have you can use to detect the desired object?

[David Ausere]

Here are the 2 seperate things I tried.  Neither worked.

 if (menuChoice==3) {
                 
               int delid;
               System.out.println("Please input Student ID: ");
               delid = Integer.parseInt(input.nextLine());
               int removeID; 
               removeID = int.indexOf(delid);

And

if (menuChoice==3) {
try {
    System.out.print("Please input Student ID: ");
    int removeID = studentsIds.indexOf(new Scanner(System.in).nextInt());
     
    if (removeID != -1) {
        System.out.println("removeID is " + removeID);
    } else {
        System.out.println("That student ID does not exist");
    }
     
} catch (InputMismatchException e) {
    System.out.println("Input must be a valid integer");
}

[David Ausere]

My arraylist name is
ArrayList<Student> Roster = new ArrayList<>();

[Norm Radder]

Neither worked.  

Please copy the full text of the error messages and paste them here so we can see where the error is and also see what the compiler thinks is wrong.

[David Ausere]

Here is my Superclass if that helps.

// This is the Superclass

public class Student
{
    private final int ID;
    private final String fname;
    private final String lname;
    private final String em;
    private final int a;
    private final int g1;
    private final int g2;
    private final int g3;

    public Student( int studentID, String firstName, String lastName, 
                    String email, int age, int grade1, int grade2, int grade3 )
    {
        ID = studentID;
        fname = firstName;
        lname = lastName;
        em = email;
        a = age;
        g1 = grade1;
        g2 = grade2;
        g3 = grade3;
    }

    public int getStudentID()
    {
        return ID;
    }
 
    public String getFirstname()
    {
        return fname;
    }
    
    public String getLastname()
    {
        return lname;
    }
  
    public String getEmail()
    {
        return em;
    }
   
    public int getAge()
    {
        return a;
    }

    public int getGrade1()
    {
        return g1;
    }

    public int getGrade2()
    {
        return g2;
    }

    public int getGrade3()
    {
        return g3;
    }
    
       public String toString()
    {
        return " Student ID " + ID + " First name: " + fname + " Last name: " 
                + lname + " Email: " + em + " age: " + a + 
               " Grade 1: " + g1 + " Grade 2: " + g2 +
               " Grade 3: " + g3;
    }

}

[Campbell Ritchie]

Ivan Pronin, welcome to the Ranch

[Piet Souris]

@David,

if I understand correctly, you want to remove a Student whose ID you have. Right?

If so, have a look at the API of the Collection class. It has a very handy method: removeIf(Predicate<? super E> filter).
For instance: Roster.removeIf(student -> student.shoeSize == 40);

[David Ausere]

Thank you Piet,

This way MOSTLY works!  Issue I am running into with code is this.

Lets say I have 5 students.  I delete the 5th (ID 5) student and viola he gets deleted.  Here is where the problem arises.  Now I cannot delete the last student in the array after that (student ID 4) but I CAN delete all the other students.

Here is what my code looks like.  Do you see what may be causing this?

if (menuChoice==3) {
               
               int delid;
               System.out.println("Please input Student ID: ");
               delid = Integer.parseInt(input.nextLine());
               int getNumRoster=Roster.size();
               int rosterSize = getNumRoster;
               
                    if (delid <= rosterSize && delid >= 1)   {
                    System.out.println("Do you want to Delete Student ID #" 
                                    + delid + "?  Type YES" );
                    String response =  input.nextLine();
               
                    if (!response.equals("YES")) System.out.println("ID NOT "
                            + "DELETED.  YES not recognized");
                    else {
                   Roster.removeIf(student -> student.ID == delid);
                   System.out.println("ID record Deleted");
                   }
            }
               else System.out.println("ID NOT RECOGNIZED!");                                 
            }              

[David Ausere]

Or if I delete ANY student the last student cannot be deleted after that.

[Norm Radder]

Can you make a small simple program that compiles, executes and shows the problem.  
Build an ArrayList, add elements and then use the removeIf() method the in the way you are reporting the problem so we can see the problem that you are seeing.

Or if that is too hard, add some print statements to your code that prints out the values of the variables used and the contents of the arraylist to show what you are talking about.

[David Ausere]

Here is the program all in one.

import java.util.*;

public class Student
{
    private final int ID;
    private final String fname;
    private final String lname;
    private final String em;
    private final int a;
    private final int g1;
    private final int g2;
    private final int g3;

    public Student( int studentID, String firstName, String lastName, 
                    String email, int age, int grade1, int grade2, int grade3 )
    {
        ID = studentID;
        fname = firstName;
        lname = lastName;
        em = email;
        a = age;
        g1 = grade1;
        g2 = grade2;
        g3 = grade3;
    }

    public int getStudentID()
    {
        return ID;
    }
 
    public String getFirstname()
    {
        return fname;
    }
    
    public String getLastname()
    {
        return lname;
    }
  
    public String getEmail()
    {
        return em;
    }
   
    public int getage()
    {
        return a;
    }

    public int getgrade1()
    {
        return g1;
    }

    public int getgrade2()
    {
        return g2;
    }

    public int getgrade3()
    {
        return g3;
    }
    
       public String toString()
    {
        return " Student ID " + ID + " First name: " + fname + " Last name: " + lname + 
               " Email: " + em + " age: " + a + 
               " Grade 1: " + g1 + " Grade 2: " + g2 +
               " Grade 3: " + g3;
    }

    public static void main(String[] args) 
    {
       ArrayList<Student> Roster = new ArrayList<>();
       Scanner input = new Scanner(System.in);

       int menuChoice = 4;
       
       do {
           System.out.println("\t\tStudent Roster Menu");
           System.out.println("\t\t1. Add Student");
           System.out.println("\t\t2. View Students");
           System.out.println("\t\t3. Delete Student");
           System.out.println("\t\t4. Exit");
           try {
               System.out.println("Enter a choice: ");
               menuChoice = Integer.parseInt(input.nextLine());
           } catch (NumberFormatException e) {
               continue;
           }
                      
           if (menuChoice==1)
           {                                                           
               int getNumRoster=Roster.size();
               int ID = getNumRoster + 1;
               System.out.println("Your Student ID is: " + ID);
               
               System.out.println("First name: ");
               String fname = input.nextLine();
               
               System.out.println("Last name: ");
               String lname = input.nextLine();
               
               System.out.println("Email: ");
               String email = input.nextLine();

               int age;
               System.out.println("Age: ");
               age = Integer.parseInt(input.nextLine());
               
               int grade1;
               System.out.println("Grade 1: ");
               grade1 = Integer.parseInt(input.nextLine());

               int grade2;
               System.out.println("Grade 2: ");
               grade2 = Integer.parseInt(input.nextLine());

               int grade3;
               System.out.println("Grade 3: ");
               grade3 = Integer.parseInt(input.nextLine());

               Student students = new Student (ID, fname, lname, email, age, grade1, grade2, grade3);
               Roster.add(students);
            
            } if (menuChoice==2) {
               System.out.println("Students: ");
               Roster.forEach((students) -> {
                   System.out.println(students);
               });
           }
           
            if (menuChoice==3) {
               
               int delid;
               System.out.println("Please input Student ID: ");
               delid = Integer.parseInt(input.nextLine());
               int getNumRoster=Roster.size();
               int rosterSize = getNumRoster;
               
                    if (delid <= rosterSize && delid >= 1)   {
                    System.out.println("Do you want to Delete Student ID #" 
                                    + delid + "?  Type YES" );
                    String response =  input.nextLine();
               
                    if (!response.equals("YES")) System.out.println("ID NOT "
                            + "DELETED.  YES not recognized");
                    else {
                   Roster.removeIf(student -> student.getStudentID() == delid);
                   System.out.println("ID record Deleted");
                   }
            }
               else System.out.println("ID NOT RECOGNIZED!");                                
            }                    
       } while (menuChoice<4);
    }
}

Run it.  Add 5 or so students then start deleting students.  You will see.

[Norm Radder]

Add 5 or so students then start deleting students.

Could you write a test driver that does all that to make our testing easier and so that the tester would see exactly what you see when the problem happens?

One way is to load all the responses to the Scanner next methods in the Scanner class's constructor as a String:
 

     Scanner input = new Scanner("1 .... "); //System.in);

replace the ... with all the necessary responses for the testing.

Or put all of the user input in a file: StudentData.txt
and change the Scanner constructor to read from that file:
   

     Scanner input = new Scanner(new File("StudentData.txt"); //System.in);

               else System.out.println("ID NOT RECOGNIZED!");                                

That message should include the values of the variables that cause it to be printed.

[Piet Souris]

Whatever the cause, there is a flaw in the way you determine the Student ID. See the code for (menuChoice == 1). If you start afresh, then add 4 students, they get the ID's of 1, 2, 3, 4.

Now, delete student 1. Assuming that is successfull, can you now see, in the code (menuChoice == 3), why you cannot delete student 4? And also, if you add a new student, what ID does that student get?