Question

How to check the sizeof array list in java without get error exception from the compiler if the arraylist is not been initialised.
I have tried the following but it does not work. and I got this message:
Exception in thread “main” java.lang.IndexOutOfBoundsException: Index: 1, Size: 1

ArrayList<String> str = new ArrayList<>();
if (str.size()>0)

Answer 1

There is nothing in the code you posted that would throw an IndexOutOfBoundsException. I assume you were calling str.get(0) without the size check before?

Anyway, your code is fine, i.e. you should be able to extend it to do something like the following:

List<String> someStrings = new ArrayList<String>();
...
if (someStrings.size() > 0) {
    System.out.println("First element of list is: " + someStrings.get(0));
} else {
    System.out.println("List is empty");
}

However, for cleanliness I would suggest using if (!someStrings.isEmpty()) instead, which checks the same thing as if (someStrings.size() > 0).