Java 将数据从 2 数组列表复制到 2 维数组

Question

Can anyone please share an example to store the resultset to a 2 dimensional array. First column on the database table have dependency on second column. I don't think array list will work if the columns have dependencies.

 ResultSet rs = stmt.executeQuery(sql);

 List a1 = new ArrayList();
 List a2 = new ArrayList();
 
// List<List> arraylist2D = new ArrayList<List>();
 
 
 

while(rs.next()){
    
    
    
    
     a1.add(rs.getString("ID"));
     a2.add(rs.getString("ID"));
     
     
    //Display values
    
     
}

Assigned to array list but need to copy to 2 dimensional array. Thanks

Answer 1

NOTE: Your list initialization has no object class so it will have an error. Therefore, I'll assume you are handling Integers (It doesn't really matter though).

I'm not sure what you mean by your post as it isn't worded the best but I'll try my best. You need to initialize a 2d array with a width of the length of the largest ArrayList (unless they are the same, then it doesn't matter). Then, you fill it in. Here is the code:

List<Integer> a1 = new ArrayList();
List<Integer> a2 = new ArrayList();
int[][] arr2d = new int[a1.size()][2/*two arraylists*/];

for (int i = 0; i < a1.size(); i++) {
    arr2d[i][0] = a1.get(i);
    arr2d[i][1] = a2.get(i);
}

This works flawlessly and without error. Hope I helped!