如何将变量添加到数组列表，然后汇总 arraylist 的所有元素？

Question

I'm trying to input a variable into an ArrayList and then add all the elements. How can i do that? The code I tried is below. Thanks.

ArrayList<String> aListNumbers = new ArrayList<String>();
int abc = 23;
aListNumbers.add("abc");
aListNumbers.add("2");
aListNumbers.add("3");

//Java ArrayList Sum All Elements

int sum = 0;
for(int i=0; i < aListNumbers.size(); i++){
    sum = sum + Integer.parseInt(aListNumbers.get(i));
}

System.out.println("Sum of all elements of ArrayList is " + sum);

Answer 1

aListNumbers.add("abc");

Here you aren't adding the contents of the variable named abc to the list. You're adding the String "abc" to the list. This will cause a NumberFormatException when the code tries to parse the character string "abc" into a number - because "abc" just isn't a number.

aListNumbers.add(abc);

That's closer to what you want, but it will still complain because the variable abc isn't a String. Since aListNumbers expects Strings (as it is an ArrayList<String> ), trying to add anything else will upset the compiler.

aListNumbers.add(Integer.toString(abc));

Will work.

Answer 2

Use an ArrayList<Integer> instead of String?

Answer 3

The OP does not know how to code in java. The error is obvious and is not worthy of this site.

BUT!

If you spend the time to type anything - I would rather give an answer. Even though its been a couple of decades since I was in those shoes - I remember very well when a simplest thing makes one stuck for hours if not days - I was fortunate to be coding in the same room with really patient (not just knowledgeable) people. So I am for giving the guy some slack.

and the answer is - definitely use ArrayList<Integer>

but also doing add - don't add("2") - this is adding a string, instead add(2) which adds an integer

and if you really want to parse those strings then you should have String abc="23";

the more valuable bit of info is - find examples - the web is full of them - get your questions answered faster and avoid disdain.

peace