More than once in an arrayList with user input

Question

In the code below I need to check if a number appears more than once in an ArrayList. The user inputs a number to consult, and if it exist in the array and there are more than one the messages, "appears more than once is displayed". I have been trying to do this but I don't know how.

This is the main class:

    ArrayList<Integer> list = new ArrayList<>();
    list.add(3);
    list.add(2);
    list.add(7);
    list.add(2);

    System.out.println("Type a number: ");
    int number = Integer.parseInt(sc.nextLine());
    if (Metodos.moreThanOne(list, number)) {
        System.out.println(number + " appears more than once.");
    } else {
        System.out.println(number + " does not appear more than once.");
    }

This is the method:

public static boolean moreThanOne(ArrayList<Integer> list, int number) {
    for (Integer in : list) {
        if (list.contains(number) && in==in) {
            return true;
        }
    }
    return false;
}

Dmitry Zagorulkin · Accepted Answer · 2016-05-05 07:17:50Z

5

You can use this code:

if (list.lastIndexOf(element) != list.indexOf(element)) {
  return true; // you have at least two numbers
} else {
  return false; // element is not exist or you have only one element
}

answered May 5, 2016 at 7:17

Dmitry Zagorulkin

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5 Comments

Roland Illig Over a year ago

Why not directly this? return list.lastIndexOf(element) != list.indexOf(element);

Dmitry Zagorulkin Over a year ago

@RolandIllig because if requested element is not exist you will get -1 from the left and from the right

Roland Illig Over a year ago

But your code does exactly the same, just with more lines.

Dmitry Zagorulkin Over a year ago

@RolandIllig excuse me, it is the same

Roland Illig Over a year ago

Oh no, not this if true return true else false pattern again.

Slim · Accepted Answer · 2016-05-05 07:16:00Z

1

    public static boolean moreThanOne(ArrayList<Integer> list, int number) 
    {
      int count = 0;
      for (Integer in : list) {
          if (number == in) {
              count++;
          }
      }
      if(count > 1)
         return true;
      else 
         return false;
      }
    }

edited May 5, 2016 at 7:16

Slim

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answered May 5, 2016 at 7:11

Alikbar

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Comments

SpaceCore186 · Accepted Answer · 2016-05-05 07:44:43Z

0

You can do this:

public class StartHere {
public static void main(String[] args) {

    ArrayList<Integer> list = new ArrayList<>();
    list.add(3);
    list.add(2);
    list.add(7);
    list.add(2);

    Scanner scanner = new Scanner(System.in);

    System.out.print("Type a number: ");
    String input = scanner.nextLine();
    int number = Integer.parseInt(input);
    scanner.close();
    if(moreThanOnce(list, number)){
        System.out.println("The number appears more than once.");
    }else{
        System.out.println("The number doesn't appear more than once.");
    }

}

public static boolean moreThanOnce(ArrayList<Integer> list, int number) {
    boolean bool = false;
    int counter = 0;
    for (Integer value : list) {
        if (value == number) {
            counter++;
        }
    }
    if (counter > 1){
        bool = true;
    }
    return bool;
}
}

Just a tip: you should improve your english, so it's easier to understand your question. A great way of doing this is reading books wrote in this language.

edited May 5, 2016 at 7:44

answered May 5, 2016 at 7:32

SpaceCore186

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3 Comments

Exit Over a year ago

I have tried that, doesnt work, if you input 3 or 7, the message "The number appears more than once." is displayed, you are only checking if the number is on the list.

SpaceCore186 Over a year ago

Ooooh... Wait a second, I'll fix it.

Exit Over a year ago

Is the same answer posted by Alikbar, Thanks Anyway

VishalZ · Accepted Answer · 2016-05-13 12:42:41Z

0

    System.out.println("Type a number: ");
    Set<Integer> set = new HashSet<Integer>(list);
    Scanner scanner = new Scanner(System.in);
    int number = Integer.parseInt(scanner.nextLine());

    if (!set.add(number)) {
        System.out.println(number + " appears more than once.");
    } else {
        System.out.println(number + " does not appear more than once.");
    }

answered May 13, 2016 at 12:42

VishalZ

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