猫文本文件到标准输入导致数组为空？

Question

I'm cating a file using the cat text-file | Java my-program on my terminal

the result when I print the lines after i store it into a array results in null can someone explain why?

            Scanner scan2 = new Scanner(System.in);
            Scanner scan = new Scanner(System.in);//create new scanner object
            int index = 0;//create index to increment through array
            while(scan.hasNextLine()){//while looop to execute if file has length
                String line = scan.nextLine();//store line into string input
                count++;
            }

            if(count < BUFSIZE){
                stringArray = new String[count];
            }
            else{
                stringArray = new String[BUFSIZE];
            }

            while(scan2.hasNextLine()){
                String line2 = scan2.nextLine();  
                if(index > stringArray.length-1)
                {
                    stringArray = expandArray(stringArray,BUFSIZE);//call method to increase array length
                }
                stringArray[index] = line2;//store line into array at given index
                index++;//increment index
            }
            /*while(sorted){
                sorted = false;
                for(int i = 0; i < stringArray.length-1; i++){
                    if(stringArray[i].compareTo(stringArray[i+1]) > 0){
                        temp = stringArray[i];
                        stringArray[i] = stringArray[i+1];     
                        stringArray[i+1] = temp;
                        sorted = true;
                    }
                }
            }*/
            for(int i = 0; i < stringArray.length; i++){
                System.out.println(stringArray[i]);
            }
        }       
    } 

    private static String [] expandArray(String [] array, int extend){
        String newArray [] = new String[array.length+extend];//create new array with given array and int as length to extend
        //for loop to copy data from old array into new created array
        for( int i = 0; i  < array.length; i++){
            newArray[i] = array[i];
        }
        return newArray;//return newly created array
    }
}

the program bubble sorts the array of strings. If I read in the file through Scanner file its fine, but why I cat it doesn't. The expand array method is to dynamically expand the array every-time it reaches max capacity. Thank you

Answer 1

The following is wrong:

Scanner scan2 = new Scanner(System.in);
Scanner scan = new Scanner(System.in);//create new scanner object

Basically, each scanner grabs the System.in stream, but streams can only be read once . You should change your code to use only one scanner, and then only use it once.

When you wrote the program to use a file, the Scanner would actually open two streams to the file so that it can be read twice, but this won't work when all you have is one stream.

EDIT:

Here is a version where you use only one Scanner (and thus one stream) :

        Scanner scan = new Scanner(System.in);//create new scanner object
        int count = 0;
        stringArray = new String[BUFSIZE];
        while (scan.hasNextLine()){//while looop to execute if file has length
            String line = scan.nextLine();//store line into string input
            if (count >= stringArray.length) {
                //call method to double array length
                stringArray = expandArray(stringArray, stringArray.length);
            }
            stringArray[count] = line;
            count++;
        }
        // Shrink array to required size
        String[] temp = stringArray;
        stringArray = new String[count];
        System.arraycopy(temp, 0, stringArray, 0, count);

Please note I didn't test it, but this is conceptually how you could do it.

The other alternative is to use an ArrayList<String> which will automatically expand and shrink.

Answer 2

Scanner scan = new Scanner(System.in);
List<String> list = new LinkedList<>();
while(scan.hasNext()) list.add(scan.next());
scan.close();
Collections.sort(list);
for(String line : list) System.out.println(line);

lol

UPDATE @JBert:

System.out.println(StringUtils.join(Ordering.<String>natural().sortedCopy(IOUtils.readLines(System.in)), "\r\n"));

looool

Answer 3

In this code

while(scan2.hasNextLine()){
    String line2 = scan2.nextLine();  
    if(index > stringArray.length-1)

you are doing something if index is greater than the length of the array, but no doing anything otherwise.