你的代码每次都是除以10，这可以用来反向打印值。要向前打印它，你需要一个包含对数的位more math。有时像这样，

Scanner input = new Scanner(System.in);
System.out.print("Enter an integer: ");
int temp = input.nextInt();
while (temp > 0) {
    int p = (int) (Math.log(temp) / Math.log(10));
    int v = (int) (temp / Math.pow(10, p));
    System.out.print(v + " ");
    temp -= v * Math.pow(10, p);
}

或者，读取一行输入。去掉所有非数字，然后打印每个字符，用空格隔开。例如，

String temp = input.nextLine().replaceAll("\\D", "");
System.out.println(temp.replaceAll("(.)", "$1 "));

你的大部分代码都是正确的，你要做的是除以10，然后打印出值--这可能应该是一个取模运算%，以获得运算的余数并打印出来--但这是一个很好的思考方式。
尽管如此。
您可以只使用一个字符串，然后在每个字符上拆分该字符串

public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter an integer: ");

        // we know that we are going to get some input - so we will just grab it as a String
        // whilst we are expecting an int - we will test this later.
        // we are doing this as it makes it easier to split the contents of a string
        String temp = input.next();

        // is this an int? - we will test this first
        try {
            // if this parsing fails - then it will throw a java.lang.NumberFormat exception 
            // see the catch block below
            int test = Integer.parseInt(temp);
            
            

            // at this point it is an int no exception was thrown- so let's go 
            // through and start printing out each character with a space after it

            // the temp(which is a string).toCharArray returns a char[] which we
            // can just iterate through and set the variable of each iteration to 'c'
            for (char c : temp.toCharArray()) {
                
                // now we are going to print out the character with a space after it
                System.out.print(c + " ");
            }

        } catch (NumberFormatException ex){
            // this is not an int as we got a number format exception...

            System.out.println("You did not enter an integer. :(");
        }

        // be nice and close the resource
        input.close();
    }

您可以使用以下单行代码来单独回答您的问题。

int test = 123;
System.out.println(String.join(" ", Integer.toString(test).split("")));

输出为：1 2 3