Java indexOfMaxInRange

Question

I am doing a project for my Java class and I can't figure out how to find the index of the max time and I need help to get this method working.

public class ReservationList {
        Reservations[] reservationsArray;
        String name, phone, time;
        int index, numberInAParty;

    public ReservationList(int size) {
        reservationsArray = new Reservations[size];
    }

    //Adds items to the reservations array
    public void addArrayItem(int index, Reservations reservation) {        
        this.reservationsArray[index] = reservation;
    }

    //Finds the index of the highest number
    public static int indexOfMaxInRange (ReservationList list, int low, int high) {
        int timeZero = Integer.valueOf(list.reservationsArray[0].time.replace(":", ""));        
        int max = timeZero;        
        int maxIndex = 0;    
        for (int i = low; i < high; i++) {            
            int time = Integer.valueOf(list.reservationsArray[i].time.replace(":", ""));         
            if (time > max) {
                System.out.println("Pass");
                maxIndex = i;
                //max = Integer.valueOf(list.reservationsArray[i].time);
            }
        }
        return maxIndex;
    }

    //Swaps array elements
    private static void swapElement (ReservationList list, int indexOne, int indexTwo) {
        Reservations temp = list.reservationsArray[indexOne];
        list.reservationsArray[indexOne]= list.reservationsArray[indexTwo];
        list.reservationsArray[indexTwo]= temp;
    }

    //Sorts through the array
    protected static void sortArray(ReservationList list) {  
        for(int i = list.reservationsArray.length;i >= 0; i--){
            int big = indexOfMaxInRange(list,0,i);
            swapElement(list, big,i);
        }
        for(int i=list.reservationsArray.length;i>0;i=i-1){
            swapElement(list,i,i-1);
        }   
    }
}

public class Reservations {

    protected String name;
    protected String phone;
    protected int numberInAParty;
    protected String time;


    public Reservations() {
        this.name = "";
        this.phone = "";
        this.time = "";
        this.numberInAParty = 0;
    }

    public Reservations(String name, String phone, String time, int numberInAParty, int size) {
        this.name = name;
        this.phone = phone;
        this.time = time;
        this.numberInAParty = numberInAParty;
    }

    public void printReservation (Reservations x) {
        System.out.println("Name: " +  x.name);
        System.out.println("Phone number: " + x.phone);
        System.out.println("Time: " + x.time);
        System.out.println("Party number: " + x.numberInAParty);
    }

}

Here is how the list is initialized

private void loadArray (String fileName, ReservationList list) throws IOException, FileNotFoundException {
    BufferedReader reader = new BufferedReader (new InputStreamReader(new FileInputStream(fileName)));     
    Reservations temp = new Reservations();
    String reservation;

    int i = 0;
    String delimiters = "[ ]+";        

    try {                        
        while ((reservation = reader.readLine()) !=null) {
            String[] splitReservation = reservation.split(delimiters);
            temp.name = splitReservation[0];
            temp.phone = splitReservation[1];
            temp.numberInAParty = Integer.valueOf((String)splitReservation[2]);
            temp.time = splitReservation[3];

            list.addArrayItem(i, temp);
            list.sortArray(list);
            ReservationsTextArea.append(list.reservationsArray[i].name + "  " + list.reservationsArray[i].phone + "  " + list.reservationsArray[i].numberInAParty + "  " + list.reservationsArray[i].time + "\n");                                                
            i++;
        }


    } catch (NumberFormatException e) {
        System.out.println(e.getMessage());
    }                        
}

Let me know if you need more of the code. This is my first time posting so let me know if I did anything wrong.

I am inputting an object that contains a name, phone number, party amount, and time. This method is supposed to sort the times so that the smallest time is first and latest time is last.

I get a nullpointerexception after it prints out pass, it is just there for debugging purposes. It works if I replace max with 0 however and I don't understand why. Let me know if you need anything more.

I didn't create some of these methods so don't criticize any of it please. All I want it to fix what is specified. Sorry that it is ridiculously long. Our group used the swing editor in NetBeans to make it to save time, please don't comment about how Im not gonna learn anything etc. I know.

The method that adds the objects are loadArray and DisplayAllButtonActionPerformed calls that method

I'm also aware that sortArray is in a loop and until it works I am just keeping it there.

It will help a lot to give sample input and the output your program is trying to generate — swapz83, Dec 16 '15 at 00:58
So you have a list class that holds an array of some type of `Reservations` object with a time field? Can you add all those relevant classes please? What is the purpose of the `ReservationList` class itself? — OneCricketeer, Dec 16 '15 at 01:10
Now that you've added your classes. Still a bit confused on your object modelling. Why does `ReservationList` itself have a name and time and all those other fields part of `Reservations`? You also forgot to include where you actually insert Reservation objects into the list. — OneCricketeer, Dec 16 '15 at 01:23
The expected result is to have it sort the time in an array so that 6:30 is below 8:30 etc — Sandpiper131, Dec 16 '15 at 01:23
There is another class that does all that stuff, I myself did not make this class another classmate did and we are supposed to use the name and time field but in a different class I just have it take the whole object instead. — Sandpiper131, Dec 16 '15 at 01:24
Without seeing where the objects are added. The whole array contains null values when you do `new Reservations[size]` — OneCricketeer, Dec 16 '15 at 01:29
Alright, so I'll let all that other stuff slide if you provide the format of the time string. Is it just `hour:minute`? — OneCricketeer, Dec 16 '15 at 01:37
Alright. You do realize that will cause issues when comparing times. 1 PM should be considered greater than 1 AM. — OneCricketeer, Dec 16 '15 at 01:58
It only goes from 5:30PM to 8:30PM, sorry for all the missing information. — Sandpiper131, Dec 16 '15 at 02:01

score 2 · Answer 1 · answered Dec 16 '15 at 01:58

2

Change your loadArray code so that a new Temp Object is created in each iteration of the loop

while ((reservation = reader.readLine()) !=null) {
   Reservations temp = new Reservations();
   temp.name = splitReservation[0];
   // etc

otherwise you are always working on the same Object

answered Dec 16 '15 at 01:58

Scary Wombat

44,617
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It doesn't fix the problem, but thanks for the advice. – Sandpiper131 Dec 16 '15 at 02:03
@Sandpiper131 - You should still do it, though. Otherwise every object in the list has the same information. – OneCricketeer Dec 16 '15 at 02:04
No it doesn't because it reads off of a separate file. Don't worry it changes. And I did do it but it doesn't change anything on how the program functions. Sorry if I am just being stupid though. – Sandpiper131 Dec 16 '15 at 02:07
1

Use a debugger, it will show that all Objects are the SAME object. – Scary Wombat Dec 16 '15 at 02:12
BTW, you could greatly simplify your code just be using a Map – Scary Wombat Dec 16 '15 at 02:14

OneCricketeer · Answer 2 · 2015-12-16T02:40:26.910

I haven't been able to narrow down the NullPointerException, so you may want to debug the file that you are reading in and check the array after reading in all your data.

The problems I did find so far, though, are that the sortArray is wrong. You initialize i = list.length, which would throw an IndexOutOfBoundException. You also have the same for-loop twice for some reason.

So here is the fix for that (which I verified sorts ascending).

protected static void sortArray(ReservationList list) {
    for (int i = list.reservationsArray.length - 1; i >= 0; i--) {
        int big = indexOfMaxInRange(list, 0, i);
        swapElement(list, big, i);
    }
}

As for the max index method. There has to be somewhere you are getting a null object in order for you to get that error. From my simple testing, this works for me.

public static int indexOfMaxInRange(ReservationList list, int low, int high) {
    int max = Integer.MIN_VALUE; // Set this to be the lowest possible integer
    int maxIndex = low;

    for (int i = low; i < high; i++) {
        String timestamp = list.reservationsArray[i].time.replace(":", "");
        int time = Integer.valueOf(timestamp);

        if (time > max) {
            maxIndex = i;
            max = time;
        }
    }
    return maxIndex;  // note if low >= high, low is returned
}

You also don't need to sort the array every single time you add a Reservations object, so do something like

 try {                        
    while ((reservation = reader.readLine()) != null) {            
        String[] splitReservation = reservation.split("\\s+"); // this is the proper delimiter you want

        Reservations temp = new Reservations();
        temp.name = splitReservation[0];
        temp.phone = splitReservation[1];
        temp.numberInAParty = Integer.valueOf(splitReservation[2]);
        temp.time = splitReservation[3];

        list.addArrayItem(i, temp);                                      
        i++;
    }
} catch (NumberFormatException e) {
    System.out.println(e.getMessage());
}     
ReservationList.sortArray(list); // this is a static method, so treat it like one

@Sandpiper131 - I'm sorry this code didn't help you, but that doesn't give you the right to completely invalidate the work I put into helping you. I recreated all the necessary pieces of your project and got all these methods to work fine. If you truly want to learn how to code, learn to use a debugger to walk through your code. Even forget the GUI and build out smaller modules like I did to make sure your logic works. — OneCricketeer, Dec 16 '15 at 04:33

Java indexOfMaxInRange

2 Answers2