从文本文件读入数组-获取“空”

Question

I'm reading from a file and copying that into an array. My file has five lines of text, a sentence each. I get my output "Array size is 5" but nothing after that. If I do add a print line of the array, it gives me 5 nulls...

Can someone help explain what I did wrong? Thanks!

 public static int buildArray() throws Exception { System.out.println("BuildArray is starting "); java.io.File textFile; // declares a variable of type File textFile = new java.io.File ("textFile.txt"); //reserves the memory Scanner input = null; try { input = new Scanner(textFile); } catch (Exception ex) { System.out.println("Exception in method"); System.exit(0); } int arraySize = 0; while(input.hasNextLine()) { arraySize = arraySize + 1; if (input.nextLine() == null) break; } System.out.println("Array size is " + arraySize); // Move the lines into the array String[] linesInRAM = new String[arraySize];// reserve the memory int count = 0; if (input.hasNextLine()) { while(count < arraySize) { System.out.println("test"); linesInRAM[count] = input.nextLine(); System.out.println(linesInRAM[count]); count = count + 1; } } 

Answer 1

In this code

    int count = 0;
    if (input.hasNextLine())   

The above hasNextLine will always be false as you have already read all the way through the file.

Either reset the scanner to the beginning of the file, or use a dynamic list eg ArrayList to add the elements to.

Answer 2

My Java is a bit rusty, but the basic gist of my answer is that you should create a new Scanner object so that it reads from the beginning of the file again. This is the easiest way to "reset" to the beginning.

Your code is currently not working because when you call input.nextLine() you're actually incrementing the scanner, and thus at the end of that first while() loop input is sitting at the end of the file, so when you call input.nextLine() again it returns null .

Scanner newScanner = new Scanner(textFile);  

Then in the bottom of your code, your loop should look like this instead:

if (newScanner.hasNextLine())
    { 
        while(count < arraySize) 
            {
                System.out.println("test");
                linesInRAM[count] = newScanner.nextLine();
                System.out.println(linesInRAM[count]);
                count = count + 1;
            }
    }