如何使用.nextInt .hasNextInt或.hasNext读取单行输入的整数而不会造成阻塞？

Question

I'm trying to read integers entered one after another on a single line separated by a space. There will be some way for this code to work without using .nextLine , without converting the input to a string and then do the conversion to integer? The challenge is "not use .nextLine", do not use string or conversions. Reading pure integers and exit from while loop.

public static void scannerInts (){          
        int[] list = new int[100];
        int n=0;            
        System.out.print("Input data into one line, [ENTER] to finish: ");            
        Scanner input = new Scanner(System.in);
        while (input.hasNext()) {
            if (input.hasNextInt()) {
                list[n++]= input.nextInt();
            } else {
                input.next();
            }
        }
        for (int i=0;i<n;i++)
             System.out.print(list[i] + " ");
}

PD: I've tried many of the responses from Stack OverFlow and nothing seems to work.

Answer 1

The problem is that System.in is an infinite stream. Calling hasNextXXX will cause System.in to prompt if the Scanner doesn't find a token in what has already been read. The user needs to enter some non-integer to terminate the list.

You may, however, use a second Scanner since Scanner can scan a String eg:

Scanner in = new Scanner(System.in);
System.out.print("Enter a list of integers: ");

List<Integer> list = new ArrayList<>();
Scanner line = new Scanner(in.nextLine());

// optional
line.useDelimiter("\\D+");

while(line.hasNextInt()) {
    list.add(line.nextInt());
}

System.out.println("You entered " + list);

Using a single Scanner you could also use findInLine :

for(String token; (token = in.findInLine("-?[1-9]\\d*")) != null;) {
    list.add(Integer.valueOf(token));
}