Entering (input/scanner) two same numbers consecutively to break a loop "while" Java

Question

I am a new-bee in java, I have a problem that i cant figure out to compare previous entered number(int) with next one continuously and I need to write a program that repeatedly reads numbers from the user’s keyboard. The program stops looping when the user types the same number twice in a row.

Thanks in advance for your kind guidance.

Here’s a sample run of the program: 5 13 21 5 4 5 5 Done!

Following was my unsuccessful effort :)

Scanner input = new Scanner(System.in); System.out.println("Enter Numbers");

    int x = 0;
    int y = 0;
    x = input.nextInt();
    y = input.nextInt();
    while (x != y) {

        x = input.nextInt();
        y = input.nextInt();

    }

    System.out.println("Done!!!!!!!");
    input.close();

Just store the previous value in a variable and check whether or not the new value is the same as the previous value. If so: stop loop, if not, update previous value and re-enter the loop. — MWB
– MWB, Commented Oct 31, 2018 at 7:06
Please share a code with your attempting to achieve the result. Meanwhile please read a reference How to create a Minimal, Complete, and Verifiable example — Yuriy Tsarkov
– Yuriy Tsarkov, Commented Oct 31, 2018 at 7:17
You code will only compare after entering a set of two numbers and only comparing these numbers to each other. — Scary Wombat
– Scary Wombat, Commented Oct 31, 2018 at 8:22

Oleg Cherednik · Accepted Answer · 2018-10-31 07:29:12Z

1

You can use loop to read number from console and stop if previous nubmer equals to current one. As marker of first number you can use e.g. null value of Integer prv (as alternative, you can use boolean isFirstLine flag for first line or res.isEmpty()).

public static List<Integer> receiveNumbers() {
    List<Integer> res = new LinkedList<>();
    Integer prv = null;

    try (Scanner scan = new Scanner(System.in)) {
        while (true) {
            int num = scan.nextInt();

            if (prv != null && prv == num)
                break;

            res.add(num);
            prv = num;
        }
    }

    return res;
}

edited Oct 31, 2018 at 7:29

answered Oct 31, 2018 at 7:25

Oleg Cherednik

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3 Comments

Oleg Cherednik Over a year ago

@ScaryWombat Yes. This is Integer but not int

Oleg Cherednik Over a year ago

@ScaryWombat No, this is not enough. If prv == null, then if(prv == num) throws NPE, because if(prv == num) is if(prv.intValue() == num)

Scary Wombat Over a year ago

Sorry, I was missing that

DeveLooper · Accepted Answer · 2018-11-08 06:20:37Z

0

import java.util.Scanner;

public class OngoingPractice {

public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);
    int previous, current;

    previous = keyboard.nextInt();
    current = keyboard.nextInt();

    while (current != previous) {
        previous = current;
        current = keyboard.nextInt();
    }

    System.out.println("Done!");

answered Nov 8, 2018 at 6:20

DeveLooper

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Comments

Minn Thwin Khant · Accepted Answer · 2018-10-31 07:29:42Z

-1

Just use an infinite while loop and break if the new int is equal to previous one. As a suggestion you should show how you tried.

Scanner sc = new Scanner(System.in);
    int i;
    Integer j = null;
    boolean flag = false;
    while(true) {
        i = sc.nextInt();
        if(j==null) {j=i; flag = true;}
        if(j==i&&!flag) {
            System.out.println("Done");
            break;}
        j=i;
        flag = false;
    }

Edited : if first one is -1, it won't work as in the comment. so I modified some.

edited Oct 31, 2018 at 7:29

answered Oct 31, 2018 at 7:19

Minn Thwin Khant

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2 Comments

Scary Wombat Over a year ago

what happens if the first number entered is -1

Minn Thwin Khant Over a year ago

@ScaryWombat My modification should do the job.

Deepak Gunasekaran · Accepted Answer · 2018-10-31 07:47:15Z

-1

Remember the last entered data in one variable and check it with the current data. If both matches, break the loop.

        Scanner scanner = new Scanner(System.in);            
        String previousNumber="";
        while (scan.hasNextInt()) {
          int number = scan.nextInt(); 
          if(!previousNumber.equals("") && number==Integer.parseInt(previousNumber)) { 
            break;
          }else {
            System.out.println(number);
          }            
          previousNumber=number+"";
        }

edited Oct 31, 2018 at 7:47

answered Oct 31, 2018 at 7:16

Deepak Gunasekaran

7575 silver badges13 bronze badges

2 Comments

Samoth Over a year ago

What if first number will be 0?

Deepak Gunasekaran Over a year ago

Condition can be handled

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