如何从字符串中取数字并将它们放入arrayList中

Question

I have a program that I am trying to take a set of numbers from a string separated by commas and place them into an ArrayList ; however, I'm not quite sure how to do it. So far what I have done is turn the String into an array of chars and then convert the chars into ints by using:

Character.digit(temp[i], 10)

This example is in a for loop iterating over a string. Let's say in this case "1,2,3,4" . taking the first element of the new char array and converting it to a int.

My issue is,

• A: there has to be a better way of doing this.
• B: what happens if you get a 2 or three digit number instead, eg, "34,2,3,65,125" . these will be stored as separate elements of the array when i need it to be one element.
• C: what happens if the number is a negative one, and what if that negative number is 2 or three digits long? Eg, "-123,45,3,4,-6" .

Remember that this is mean to be for any String argument.

There are lots of conditions here and I'm not sure how to solve them.

Answer 1

Consider using

• String.split() http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/String.html
• Integer.parseInt() http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/Integer.html

Regarding "any String argument," you have a choice: either fail on the strings which are not comma-separated numbers or redefine the task. Here comes the essence of the programming: you need to define everything. The easiest way (and the safest, usually) is to fail whenever you see something unexpected. Java will do it for you in this case, so enjoy.

Answer 2

you could just do:

String input = "-12,23,123123";
String[] numbers = input.split(",");
List<Integer> result = new ArrayList<Integer>();
for(String number : numbers){
    result.add(Integer.parseInt(number));
}

Answer 3

Use the String.split() function to break your String in different strings, based on the separator:

    String input="-123,45,3,4,-6";
    String[] vals=input.split(",");

    List<Integer> numbers=new ArrayList<Integer>(vals.length);
    for(String val:vals) {
        numbers.add(Integer.valueOf(val));
    }

Answer 4

First split the input String using String.split() . Then try Integer.parseInt() .

Answer 5

String testStr = "123,456,789";
String tokens[] = testStr.split(",");

ArrayList<Integer> numList = new ArrayList<Integer>();
for(int i = 0; i < tokens.length; i++)
{     
   try
   {
      Integer num = new Integer(tokens[i]);
      numList.add(num);
   } 
   catch(NumberFormatException e)
   {  
       //handle exception
   }
}

Answer 6

String input="-123,45,3,4,-6, a";
String[] vals=input.split(",");

List<Integer> numbers=new ArrayList<Integer>(vals.length);
for(String val:vals) {
    try {
        int a = Integer.valueOf(val);
        numbers.add(a);
    } catch (NumberFormatException e) {
        // TODO: handle exception
    }
}

Use this code. By using it you can also avoid non-integer values if there any.

Answer 7

您还可以使用StringTokenizer将字符串拆分为子字符串，然后使用Integer.parseInt将它们转换为整数。