Java中的ArrayList和.add（）方法

Question

I am writing a program that has to read information from file and put them into ArrayList, I think my code is right but Eclipse is saying : The method add(int, String[]) in the type ArrayList<String[]> is not applicable for the arguments (int, String) about account.add(0, x[0]); in my code.

My code:

public static void main(String args[]) {

    ArrayList<String[]> account = new ArrayList<>();
    String line = "";
    try {
        FileReader fr=new FileReader("information.txt");

        Scanner information = new Scanner(fr);
        while (information.hasNext()) {

            // find next line
            line = information.next();

            String x[]=line.split("-");
            account.add(0, x[0]);
            account.add(0, x[1]);
            account.add(0, x[2]);
        }
    }
}

Answer 1

This is the signature of the method you're using :

public void add(int index, E element) { ... }

You have ArrayList<String[]> , so the method expects an array of Strings as a second param. And what you provide is just a String (element from the array).

Try this:

String x[]=line.split("-");
account.add(0, x); // because x is actually an array

Or you can use it like that:

account.add(x);

If you still need to put elements from the array into your list like you do here:

account.add(0, x[0]);
account.add(0, x[1]);
account.add(0, x[2]);

try to change ArrayList<String[]> to ArrayList<String> .

And just a comment that has nothing to do with your question :) This is a better practice:

// use interface List in the left part :)
List<String[]> account = new ArrayList<>();

Happy hacking :)

Answer 2

You should to just write account.add(x[0]); For example:

ArrayList<String> arrayList = new ArrayList<>();
arrayList.add("smth");