Java有没有高效的2D ArrayList类？

import java.util.ArrayList;

public class TwoDArrayListExample {
    public static void main(String[] args) {
        // 创建一个嵌套的ArrayList
        ArrayList<ArrayList<Integer>> twoDArrayList = new ArrayList<>();

        // 添加行和列
        int numRows = 3;
        int numCols = 4;
        for (int i = 0; i < numRows; i++) {
            ArrayList<Integer> row = new ArrayList<>();
            for (int j = 0; j < numCols; j++) {
                row.add(i * numCols + j);
            }
            twoDArrayList.add(row);
        }

        // 访问和修改元素
        int element = twoDArrayList.get(1).get(2);
        System.out.println("Element at (1, 2): " + element);

        twoDArrayList.get(2).set(3, 99);
        System.out.println("Modified element at (2, 3): " + twoDArrayList.get(2).get(3));

        // 遍历二维ArrayList
        for (ArrayList<Integer> row : twoDArrayList) {
            for (int value : row) {
                System.out.print(value + " ");
            }
            System.out.println();
        }
    }
}