Working with a List of Lists in Java

Working with a List of Lists in Java involves using nested List objects, where each element of the outer list is itself a list. This is useful for representing multi-dimensional data structures, such as tables or matrices.

Here’s how you can work with a List of Lists in Java:

Declare a List of Lists: To declare a List of Lists, you typically use the List> syntax. For example:

  List> listOfLists = new ArrayList<>();

Add Lists to the List of Lists: You can add lists as elements of the main list. For example:

List innerList1 = Arrays.asList(1, 2, 3);
List innerList2 = Arrays.asList(4, 5, 6);
listOfLists.add(innerList1);
listOfLists.add(innerList2);

Access Elements in a List of Lists: You can access elements using the indices of both the outer and inner lists:

  int element = listOfLists.get(0).get(1);  // Access element 2 from the first list

Iterate Over List of Lists: You can loop through the outer list and then loop through each inner list:

for (List innerList : listOfLists) {
    for (Integer num : innerList) {
        System.out.println(num);
    }
}

Benefits:

• Flexibility: Allows you to store and manage nested data efficiently.
  
• Scalability: You can dynamically add or remove lists at runtime.
  
• Data Organization: Perfect for storing matrices, tables, or hierarchical data.
  

In summary, a List of Lists in Java provides an easy way to organize multi-dimensional data and can be manipulated using standard list operations.