使用扫描仪从列表中读取整数和字符串

Question

I am reading a string from stdin that's formatted as a list. I am using the information from the string to create objects.

An example input string would be formatted as follows:

1 apple, 3 bananas, 2 pears

I want to read that line a create objects as I go, but my biggest issue is properly reading the line to get the number of items, followed by them item itself while also skipping whitespace and commas. I have tried the following:

Scanner input = new Scanner(System.in);
input.useDelimeter(",|\\s");
while(input.hasNext()){
    int numItems = input.nextInt();
    String item = input.next();

    // create object and add to object array
}

Which works for the first iteration (1 apple) but fails on the second with a type mismatch. Can anyone suggest a fix or alternate solution?

Thanks!

Answer 1

,|\\\\s declares two separate delimiters. Those delimiters can be matched in text "apple, 3" twice:

1. comma after apple

2. space before 3

   apple, 3 ^^ 12

so we split that text at two separate (middle) places, which means we split it into 3 tokens:

• "apple" ,
• "" ,
• "3" .

When in next iteration (after calling input.next() which consumes apple ) you are calling input.nextInt() Scanner tries to parse second token as int, but since it finds empty string it is throwing exception.

One of solutions would be treating [space] or ,[space] as single delimiter. You can achieve it by making comma optional:

input.useDelimiter(",?\\s");

Demo:

Scanner input = new Scanner("1 apple, 3 bananas, 2 pears");
input.useDelimiter(",?\\s");
while(input.hasNext()){
    int numItems = input.nextInt();
    System.out.println(numItems);
    String item = input.next();
    System.out.println(item);
    System.out.println("----");
}

Output:

1
apple
----
3
bananas
----
2
pears
----

Answer 2

You can spilt the input String using delimiter "," and get following output after using trim() method.

1 apple

3 bananas

2 pears

Here is the code:

 String [] array1 = input.nextLine().split(",");

 for(int i=0; i<array1.length; i++){
    System.out.println(array1[i].trim());
 }

Edit: You can further split the Strings inside for loop using delimiter space , to get the desired output.