当我尝试使用 BufferedReader 读取输入时，为什么会出现 NullPointerException？

Question

I am trying to take a multiple integer input in a single line and store all those integers into an ArrayList . This is my code:

    String[] input = new String[5]; 

    ArrayList<Integer> A=new ArrayList<>(5);

    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    
    try{
        while(br.readLine()!=null)
            input = br.readLine().split(" "); 
    }
    catch(Exception e){
        System.out.print(e);
    }
    
    System.out.println(Arrays.toString(input));

The input is like this:

2 2 1 3 1

But when I excecute the code I get a NullPointerException in this line input = br.readLine().split(" "); . How can I fix this?

EDIT: Tried using Scanner to take the input like this:

    String str="";
    Scanner s=new Scanner(System.in);

    String[] input = new String[5]; 
    ArrayList<Integer> A=new ArrayList<>(5);

    
    while(s.hasNext())
        str=s.nextLine();
    
    input=str.split(" ");
    
    System.out.println(Arrays.toString(input));  //[]

Now my array is completely empty!!

Answer 1

You have two calls to br.readLine() . While the first call will abort the loop if line is null, the second call can still read the next line which can be null (indicating end of file). Additional problem is also that the line returned by the first br.readLine() is lost.

The correct way is:

String line;
while ((line = br.readLine()) != null) {
    String[] input = line.split(" ");
}

Answer 2

There should be exactly 1 spaces between the input numbers. Also you should not start input with space or have 2 spaces joined together when you are running this code.