如何将ArrayList转换为数组数组？

Question

I'm doing my 2nd Year University software engineering project and have hit a problem. I am fairly new to the Java language (and programming in general) so there is a chance I'm just not understanding the syntax well.

I have a method that I want to be used to return an array of arrays of type Object. This is to be used in a swing JTable. Therefore each elements of the array (which are arrays themselves) are the rows in the table and the elements of the 'inner' arrays are the value of each column in that row.

I do not know how many columns there will be while coding and therefore I have made a method that generates this array of arrays depended on other objects.

This is my code:

    public Object[][] getData(ArrayList<IModule> modules) {

    ArrayList<String[]> data = new ArrayList();

    for (Iterator<IModule> m = modules.iterator() ; m.hasNext(); ) {
        IModule module = m.next();
        for (Iterator<ICoursework> c = module.getCoursework().iterator() ; c.hasNext() ; ) {
            ICoursework coursework = c.next();
            String[] row = new String[6];

            row[0] = module.getModuleTitle();
            row[1] = module.getModuleCode();
            row[2] = coursework.getTitle();
            row[3] = coursework.dateToString();
            row[4] = coursework.getLecturer().getFirstName() 
                    + coursework.getLecturer().getSecondName();
            row[5] = getSubmissionDetails(coursework, row);

            data.add(row);
        }
    }
    data.trimToSize();

    return data.toArray();
}

This obviously does not compile as the ArrayList.toArray() method returns a Object[] where I need it to return a Object[][].

As I understand it since I had an ArrayList of arrays this should be converted to an array that then contained arrays. But it does not.

If you could post an answer that would be helpful. Thank you.

Answer 1

尝试return data.toArray(new String[][]);

Answer 2

You can't do that way. Try:

public Object[][] getData(ArrayList<IModule> modules) {

    ArrayList<String[]> data = new ArrayList<String[]>();

    for (Iterator<IModule> m = modules.iterator() ; m.hasNext(); ) {
        IModule module = m.next();
        for (Iterator<ICoursework> c = module.getCoursework().iterator() ; c.hasNext() ; ) {
            ICoursework coursework = c.next();
            String[] row = new String[6];

            row[0] = module.getModuleTitle();
            row[1] = module.getModuleCode();
            row[2] = coursework.getTitle();
            row[3] = coursework.dateToString();
            row[4] = coursework.getLecturer().getFirstName() 
                    + coursework.getLecturer().getSecondName();
            row[5] = getSubmissionDetails(coursework, row);

            data.add(row);
        }
    }

    Object[][] arr = new Object[data.size()][6];

    for (int i = 0; i < data.size(); i++) {
        String[] strings = data.get(i);
        for (int j = 0; j < strings.length; j++) {
            arr[i][j] = strings[j];
        }
    }

    return arr;
}