Read user input into integer array

[varunb]

I am trying to get make a java program which takes integers from user & then store into an integer array of length "size". The only problem is that I am getting exceptions when I am about to enter numbers from console. I am using Eclipse IDE & below is my code:


import java.io.*;
import java.util.Scanner;
import java.util.*;

public class BetterProgrammerTask {

public static void main(String[] args) throws IOException {
int size = 0;
System.out.println("Enter the size of the array: ");
Scanner in = new Scanner(System.in);
size = in.nextInt();
in.close();
System.out.println("The size you enetered is " + size);
int[] a = new int[size];

Scanner in1 = new Scanner(System.in);
System.out.println("Enter the array: ");

int j=0;

while(j<size)
{
a[j]=in1.nextInt();
++j;
}
in1.close();

Arrays.sort(a);
System.out.println("The sorted array is ");
for (int i=0; i<size; i++)
{
System.out.println(a[i]);
}

}

}


Below is the exception message:

Enter the size of the array:
11
The size you enetered is 11
Enter the array:
Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at BetterProgrammerTask.main(BetterProgrammerTask.jav a:33)

[PhHein]

Get rid of the second Scanner object.

Scanner in = new Scanner(System.in);
size = in.nextInt();
System.out.println("The size you enetered is " + size);
int[] a = new int[size];
System.out.println("Enter the array: ");

int j = 0;
while (j < size) {
	System.out.print("Enter "+ (j+1) + ": ");
	a[j] = in.nextInt();
	++j;
}
in.close();

[Norm]

can you explain to the OP what happened and why he got the exception?

[PhHein]

I can only guess, as I'm not familiar with Scanner, but I reckon it boils down to the inputStream still holding the '\n' from the first nextInt() call, but please correct me if I'm wrong.

[Norm]

java.util.NoSuchElementException

If the OP would read the API doc for the Scanner nextInt() method it is explained there.
After he understands why he gets the error then he needs to look at other Scanner methods to see how he can avoid this error.

[PhHein]

Ok, I've read it and I don't get it. Might be a language thing, but why is the input exhausted?

[Norm]

I think exhausted here means that there is nothing more there.

He needs to test if anything is there by using a hasNext method.
The problem with that is that it will block waiting for something. A bit confusing to me.
hasNext() shouldn't block. If there isn't anything return false. I guess it wants to see what the next thing is and test it to be an int (or whatever).
There might be a method to call to test if the input stream is empty.

[PhHein]

I think exhausted here means that there is nothing more there.

That's what bugs me, if there is nothing more, it should wait for an input, no?
Scanner1 has read an input and is closed, fine. Scanner2 should start from scratch, but it doesn't.

The intro chapter in the API doesn't help much either leave aloe the Scanning tutorial in I/O.

[Norm]

I can't figure out how you can use Scanner. There appears no way to call a hasNext method without it possibly blocking.
I can understand the a call to a next method could fail if there isn't anything in the input.

Here's an attempt not to block on Scanner having nothing to read.The main code is from another forum thread also having Scanner problems.

import java.util.ArrayList;

import java.util.Scanner;

// Check if the scanner has any input available
// Problem because Scanner.hasNext() will block!!
class CheckScanner {

  static boolean hasNext(final Scanner sc) {
    Thread t = new Thread(new Runnable() {
      public void run() {
        sc.hasNext();  // this could block
        System.out.println("hasNext returned");
      }
    });
    t.start();
    try{Thread.sleep(10);}catch(Exception x){};   // is this long enough?
    //If thread still alive, then it must be blocked
    if(t.isAlive()) {
      t.interrupt(); // What does this do for thread blocked on I/O
      System.out.println("interrupt called");
      return false;
    }else{
      return true;  // If thread has  exited, then hasNext() returned
    }
  } // end hasNext()
} // end class

public class HangingScanner {
   /** Main method */
   public static void main(String[] args) {
      
      ArrayList<Integer> numbers = new ArrayList<Integer>();
      
      // Create a Scanner
      Scanner input = new Scanner(System.in);
      System.out.println("hasNext=" + CheckScanner.hasNext(input)); //<<<<<<<<<<<<<<<
      
      // Read all numbers
      while(input.hasNextInt()){
         System.out.print("Enter a number: ");
         
         // Convert string into integer
         int nxt = input.nextInt();
         System.out.println(" got " + nxt);
         numbers.add(nxt);
      }

      System.out.print("numbers=" + numbers);
   }
}

[PhHein]

Got it! I did a search in my backyard:
Java Programming - beginers question about taking input from console

the in.close() closes System.in, that's why the next scanner object fails, duh.

If this scanner has not yet been closed then if its underlying readable also implements the Closeable interface then the readable's close method will be invoked. If this scanner is already closed then invoking this method will have no effect.

[Norm]

Thanks for that.

[PhHein]

You're welcome, now we only need the OP to come back and to understand.

[varunb]

Got it! I did a search in my backyard:
Java Programming - beginers question about taking input from console

the in.close() closes System.in, that's why the next scanner object fails, duh.

Thanks...it solved my problem. :)