Question

Hello everyone how can I do to initialize

ArrayList<Record<T>> [] values;

with a number of rows and columns? for example, with three rows and four columns?

Answer 1

Using an array of generic type (such as ArrayList<T>) is a way to hell. The following line doesn’t even compile:

ArrayList<Record<T>>[] values = new ArrayList<Record<T>>[SIZE_ARRAY];

The compiler issues this error:

Cannot create a generic array of ArrayList<Record<T>>

The only sensible solution is to create a list of lists:

// create matrix
ArrayList<ArrayList<Record<T>>> matrix = new ArrayList<ArrayList<Record<T>>>();

// add 3 rows:
for (int i = 0; i < 3; i++) {
    ArrayList<Record<T>> row = new ArrayList<Record<T>>();
    matrix.add(row);

    // add 4 elements to each row
    for (int j = 0; j < 4; j++) {
        Record<T> record = ... // get the record
        row.add(record);
    }
}

And now you can access the element at [2][3] (last element of the last row):

Record<T> record = matrix.get(2).get(3);