Merging 2 arraylists into one

Question

I am trying to combine 2 arraylists into 1. I am receiving incompatible types error when i compile. I have no clue where my mistake is. Any help would be greatly appreciated.

ArrayList<Course> myCourse = new ArrayList<Course>(); myCourse.add(coursesTaken); myCourse.add(currentSemesterCourses);

When you're posting a question regarding an error, please include (copy and paste) the actual error message and stack trace in your question. Also, make sure you post all relevant code - the error is about incompatible types, but you don't include the declarations of coursesTaken and currentSemesterCourses, so we can't see what their types are. — Michelle
– Michelle, Commented Jun 13, 2014 at 19:21

Braj · Accepted Answer · 2014-06-13 19:24:18Z

use ArrayList#addAll() that appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator.

myCourse.addAll(coursesTaken);

instead of

myCourse.add(coursesTaken);

I hope coursesTaken is a Collection that contains item of type Course or any subclass of Course.

Elliott Frisch · Accepted Answer · 2014-06-13 19:22:51Z

You want to use ArrayList.addAll(Collection), and you could use the ArrayList(Collection) constructor as well -

ArrayList<Course> myCourse = new ArrayList<Course>(coursesTaken); myCourse.addAll(currentSemesterCourses);

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