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Thread: reading a stream of numbers from standard input

  1. #1
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    Default reading a stream of numbers from standard input

    guys, I'm trying to read a stream of numbers from standard input like: 2 3 -3 10 44 9 -1. The line ends once it read -1, but for some reason I have an endless loop... how could I read this stream of numbers one number at a time?

    int num[] = new int[5];
            char ch;
     
            BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("enter series of number: ");         
            int i = 0;
             do{ 
                 num[i] = bf.read();
                 i++;                     
            }while(num[i] != -1);
     
             int j = 0;
             while(j < num.length) {
                 System.out.println(num[j]);
                 j++;
             }


  2. #2
    Super Moderator jps's Avatar
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    Default Re: reading a stream of numbers from standard input

    you could println your variables each step of the way, and see what is going on...

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    Default Re: reading a stream of numbers from standard input

    Quote Originally Posted by jps View Post
    you could println your variables each step of the way, and see what is going on...
    I'm getting a bunch of strange numbers... I don't think I'm reading the correct input. At the same time I'm getting an outofboud exception. like I'm going beyond the 5 elements of the array

    enter series of number: 
    10 3 4 99 -1
    49
    48
    32
    51
    32
    Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
    	at wordset.Stack.main(Stack.java:67)
    Java Result: 1

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    Default Re: reading a stream of numbers from standard input

    read() returns a character, not a parsed integer... read() will return, in order: '1' (49), '0' (48), ' ' (32), '3' (51), ' ' (32), '4' (52), ' ' (32), '9' (57), '9' (57), ' ' (32), '-' (45), '1' (49) i.e. each character is read as it's encoded form according to ASCII, as seen below.

    One solution is to use a Scanner, particularly with nextInt():
      /* why hardcode the length? */
      final int[] num = new int[5];
      final Scanner scanner = new Scanner(System.in);
      System.out.println("enter series of number: ");         
      int ch;
      int i = 0;
      while (scanner.hasNextInt() && (ch = scanner.nextInt()) != -1) {
        num[i++] = ch;
      }
      int j = 0;
      while (j < 5) {
        System.out.println(num[j]);
      }
    Last edited by veeer; July 30th, 2012 at 08:06 AM.

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    Badger191 (July 24th, 2012)

  6. #5
    Junior Member hackthisred's Avatar
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    Lightbulb Re: reading a stream of numbers from standard input

    Quote Originally Posted by mia_tech View Post
    guys, I'm trying to read a stream of numbers from standard input like: 2 3 -3 10 44 9 -1. The line ends once it read -1, but for some reason I have an endless loop... how could I read this stream of numbers one number at a time?

    int num[] = new int[5];
            char ch;
     
            BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("enter series of number: ");         
            int i = 0;
             do{ 
                 num[i] = bf.read();
                 i++;                     
            }while(num[i] != -1);
     
             int j = 0;
             while(j < num.length) {
                 System.out.println(num[j]);
                 j++;
             }
    I'd recommend the following approach...
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Scanner;
     
     
    public class InputStuff {
     
    	private List<Integer> getUserInput()
    	{
    		List<Integer> list = new ArrayList<Integer>();
    		Scanner keyboard = new Scanner(System.in);
    		while(keyboard.hasNext())
    		{
    			String input = keyboard.next();
    			if(!input.equals("-1"))
    				list.add(Integer.parseInt(input));
    			else
    				return list;
    		}
    		return list;
    	}
     
    	public static void main(String[] args)
    	{
    		for (Integer number  : new InputStuff().getUserInput()) 
    		{
    			System.out.print(number + " ");
    		}
    	}
    }
    f34r th3 kut3 1z

  7. #6
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    Default Re: reading a stream of numbers from standard input

    Quote Originally Posted by hackthisred View Post
    I'd recommend the following approach...
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Scanner;
     
     
    public class InputStuff {
     
    	private List<Integer> getUserInput()
    	{
    		List<Integer> list = new ArrayList<Integer>();
    		Scanner keyboard = new Scanner(System.in);
    		while(keyboard.hasNext())
    		{
    			String input = keyboard.next();
    			if(!input.equals("-1"))
    				list.add(Integer.parseInt(input));
    			else
    				return list;
    		}
    		return list;
    	}
     
    	public static void main(String[] args)
    	{
    		for (Integer number  : new InputStuff().getUserInput()) 
    		{
    			System.out.print(number + " ");
    		}
    	}
    }
    Really? Your approach would be to make a dedicated instance method to invoke on an object that has no real purpose? You'd manually read a token using scanner.next() and *then* parse it as an integer? You'd compare the input to -1 via string equality rather than just comparing integers? You have two identical return statements when one could just be replaced by a break?

    import java.util.List;
    import java.util.ArrayList;
    import java.util.Scanner;
     
    public final class EchoSeries {
     
      private EchoSeries() { }
     
      static List<Integer> readSeries() {
        final Scanner scanner = new Scanner(System.in);
        final List<Integer> list = new ArrayList<Integer>();
        int n;
        while (scanner.hasNextInt() && (n = scanner.nextInt()) != -1) {
          list.add(n);
        }
        return list;
      }
     
      public static void main(String[] argv) {
        final List<Integer> series = readSeries();
        for (final int n : series) {
          System.out.println(n);
        }
      }
    }

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    Badger191 (July 24th, 2012)

  9. #7
    Junior Member hackthisred's Avatar
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    Default Re: reading a stream of numbers from standard input

    Because in larger codes static methods are bad, when trying to trouble shoot code on an enterprise level. Besides I'd assume this method would be used inside a class without a main() lol.

    So what's the big deal, reading in a string from the user and parsing it to an Integer... I didn't break any coding rules, one can use either or... and who cares that I used a 'return' instead of a break they can be used interchangeably in this instance.
    f34r th3 kut3 1z

  10. #8
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    Default Re: reading a stream of numbers from standard input

    Static methods are bad? So Math.sin is bad, eh? I understand what you're trying to say, but this is clearly not enterprise scale... you appear to have to some degree a naive understanding of unit testing via mocking. Not trying to start a fight, just pointing out flaws in your code. You can choose to acknowledge them.

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