How to remove the brackets [ ] from ArrayList#toString()?

Question

I have created an Array List in Java that looks something like this:

 public static ArrayList error = new ArrayList<>();

for (int x= 1         


        

Answer 1

You are probably calling System.out.println to print the list. The JavaDoc says:

This method calls at first String.valueOf(x) to get the printed object's string value

The brackets are added by the toString implementation of ArrayList. To remove them, you have to first get the String:

String errorDisplay = errors.toString();

and then strip the brackets, something like this:

errorDisplay = errorDisplay.substring(1, errorDisplay.length() - 1);

It is not good practice to depend on a toString() implementation. toString() is intended only to generate a human readable representation for logging or debugging purposes. So it is better to build the String yourself whilst iterating:

List errors = new ArrayList<>();
StringBuilder sb = new StringBuilder();
for (int x = 1; x<10; x++) { 
    errors.add(x);
    sb.append(x).append(",");
}
sb.setLength(sb.length() - 1);
String errorDisplay = sb.toString();

Note that this is not an array, just a String displaying the contents of the list. To create an array from a list you can use list.toArray():

// create a new array with the same size as the list
Integer[] errorsArray = new Integer[errors.size()];
// fill the array
errors.toArray(errorsArray );