How to create a List of Lists in Java - Step by Step Examples

How to create a List of Lists in Java ?

Answer

To create a list of lists in Java, you can use the `ArrayList` class to represent the outer list and add `ArrayList` instances as elements to create inner lists.

✐ Examples

1 Create List of Lists

In this example,

We import the necessary classes from the java.util package.
We create two inner lists named list1 and list2 using the ArrayList class.
We create an outer list named listOfLists using the ArrayList class.
We add the inner lists list1 and list2 to the outer list listOfLists.
Finally, we print the list of lists to standard output.

Java Program

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Integer> list1 = new ArrayList<>();
        list1.add(1);
        list1.add(2);
        list1.add(3);

        List<String> list2 = new ArrayList<>();
        list2.add("a");
        list2.add("b");
        list2.add("c");

        List<List<?>> listOfLists = new ArrayList<>();
        listOfLists.add(list1);
        listOfLists.add(list2);

        System.out.println("List of lists: " + listOfLists);
    }
}

Output

List of lists: [[1, 2, 3], [a, b, c]]

2 Create List of Lists with Empty Inner Lists

In this example,

We create two empty inner lists named list3 and list4.
We create an outer list named listOfListsEmpty using the ArrayList class.
We add the empty inner lists list3 and list4 to the outer list listOfListsEmpty.
Finally, we print the list of lists with empty inner lists to standard output.

Java Program

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Integer> list3 = new ArrayList<>();
        List<String> list4 = new ArrayList<>();

        List<List<?>> listOfListsEmpty = new ArrayList<>();
        listOfListsEmpty.add(list3);
        listOfListsEmpty.add(list4);

        System.out.println("List of lists with empty inner lists: " + listOfListsEmpty);
    }
}

Output

List of lists with empty inner lists: [[], []]

Summary

In this tutorial, we learned How to create a List of Lists in Java language with well detailed examples.

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How to create a List of Lists in Java - Step by Step Examples

How to create a List of Lists in Java ?

Answer

✐ Examples

1 Create List of Lists

Java Program

Output

2 Create List of Lists with Empty Inner Lists

Java Program

Output

Summary

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