How to create a List of Sets in Java

How to create a List of Sets in Java ?

Answer

In Java, you can create a list of sets using the ArrayList class for the outer list and the HashSet class for the inner sets.

✐ Examples

1 Create List of Sets

In this example,

We create two inner sets named set1 and set2 using the HashSet class.
We create an outer list named listOfSets using the ArrayList class and initialize it with the inner sets.
Finally, we iterate through the list of sets and print each set to standard output.

Java Program

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Set<Integer> set1 = new HashSet<>(Arrays.asList(1, 2, 3));
        Set<Character> set2 = new HashSet<>(Arrays.asList('a', 'b', 'c'));

        List<Set<?>> listOfSets = new ArrayList<>(Arrays.asList(set1, set2));

        for (Set<?> set : listOfSets) {
            System.out.println(set);
        }
    }
}

Output

[1, 2, 3]
[a, b, c]

2 Create List of Sets with Empty Inner Sets

In this example,

We create an empty outer list named listOfSetsEmpty using the ArrayList class.
We create two empty inner sets named emptySet1 and emptySet2.
We add the inner sets emptySet1 and emptySet2 to the outer list listOfSetsEmpty.
Finally, we iterate through the list of sets with empty inner sets and print each set to standard output.

Java Program

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Set<Integer> emptySet1 = new HashSet<>();
        Set<Character> emptySet2 = new HashSet<>();

        List<Set<?>> listOfSetsEmpty = new ArrayList<>(Arrays.asList(emptySet1, emptySet2));

        for (Set<?> set : listOfSetsEmpty) {
            System.out.println(set);
        }
    }
}

Output

[]
[]

Summary

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

◀ Previous Next ▶

Java Tutorials

Java How-Tos

How to create a List of Sets in Java

How to create a List of Sets in Java ?

Answer

✐ Examples

1 Create List of Sets

Java Program

Output

2 Create List of Sets with Empty Inner Sets

Java Program

Output

Summary

More Java Lists Tutorials