Mistakes Java Developers Make

This list summarizes the top 10 mistakes that Java developers frequently make.

Convert Array to ArrayList

To convert an array to an ArrayList, developers often do this:

List<String> list = Arrays.asList(arr);

Arrays.asList() will return an ArrayList which is a private static class inside Arrays, it is not the java.util.ArrayList class. The java.util.Arrays.ArrayList class has set(),get(), contains() methods, but does not have any methods for adding elements, so its size is fixed. To create a real ArrayList, you should do:

ArrayList<String> arrayList = new ArrayList<String>(Arrays.asList(arr));

The constructor of ArrayList can accept a Collection type, which is also a super type forjava.util.Arrays.ArrayList.