CODEWITHSUNDEEP
javacollections
user3406459
user3406459

Reputation: 3

How to use Int index to String element

Can you help me with this? I don't have any idea how to fix my code. I want to get the index from IDnumber using binarySearch from collections then I will use that IDnumber's index to get the element from the Names but Im having a problem.

I got some errors when Im running it but I dont see any errors here in NetBeans.

Here is the whole code.

public class Attendance {

    public static void main(String[] args){


        List <Integer> IDnumber = Arrays.asList(121,122,123,124,125);
        List <String> Names = Arrays.asList("Victor","Arvin","Marthie","Mariam","Argel");
        System.out.println("Log In");

        System.out.println("Enter your Student number : ");
        Scanner scanner = new Scanner(System.in);

        int StudentNumber = scanner.nextInt(); 

        int x = StudentNumber;
        String s = Names.get(x);

        System.out.println(Collections.binarySearch(IDnumber,x));
        System.out.println(" Student Name : " + s);

    }
}

Can I pass the Int index to String?

Upvotes: 0

Views: 102

Answers (6)

Paul
Paul

Reputation: 3058

You probably want:

int index = Names.indexOf(StudentNumber);

Once you have this you know the index for both the ID and the name; you don't need to do the binary search (which depends your list of IDs staying in order, and will break if not). (Binary search would be faster - but the gain is insignificant unless your list is huge.)

Or do you actually want them to type in 0, 1, 2, (etc) and not 121, 122, 123, (etc)?

BTW. Please use Java conventions - e.g. variables should be in camel case (idNumbers, names, thisIsAVariable, etc).

Upvotes: 0

SubSevn
SubSevn

Reputation: 1028

If the user enters their student number (say, 121), you're trying to do this:

String s = Names.get(121);

When there is no value at the index 121 in Names. Names is only 5 elements long. What you want to do is look up the student number in IDnumber list, then use that index of the ID as the index into Names.

Try something like:

int idIndex = IDnumber.indexOf(x);
String s = Names.get(idIndex);

Although you might consider using a Map to store the relationship between the Name and the ID. What you're doing here heavily depends on the order of the IDs and Names - any shift in the ordering and your relationship is lost.

Upvotes: 1

G. Blake Meike
G. Blake Meike

Reputation: 6715

I think you want a Map:

private static final Map<Integer, String> STUDENTS;
static {
    Map<Integer, String> m = new HashMap<Integer, String>();
    m.put(Integer.valueOf(121), "Victor");
    m.put(Integer.valueOf(122), "Arvin");
    m.put(Integer.valueOf(123), "Marthie");
    m.put(Integer.valueOf(124), "Mariam");
    m.put(Integer.valueOf(125), "Argel");
    STUDENTS = Collections.unmodifiableMap(m);
}

then...

String s = STUDENTS.get(scanner.nextInt());

Upvotes: 1

amudhan3093
amudhan3093

Reputation: 748

You should sort the Collection before you can do a binarysearch on it: Use:

Collections.sort( IDnumber );
System.out.println(Collections.binarySearch(IDnumber,x));

Upvotes: 0

muthukumar
muthukumar

Reputation: 2243

you get the value from the list of Names which contains only index of 4 .

Hence values after 4 will give java.lang.ArrayIndexOutOfBoundsException

Upvotes: 0

Boris Brodski
Boris Brodski

Reputation: 8715

The error is to assign StudentNumber to x. Instead you should do

int x = Collections.binarySearch(IDnumber, StudentNumber)

Then you will get the index of the student with the number entered (121, for example).

Then you get the name of the student like you do

String s = Names.get(x);

Upvotes: 2

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