# Sets ## Set in Java * Set is an interface which extends Collection. It is an unordered collection of objects in which duplicate values cannot be stored. * Basically, Set is implemented by HashSet, LinkedHashSet or TreeSet (sorted representation). * Set has various methods to add, remove clear, size, etc to enhance the usage of this interface ```java // Java code for adding elements in Set import java.util.HashSet; import java.util.Set; public class SetExample { public static void main(String[] args) { // Set demo using HashSet Set hash_Set = new HashSet(); hash_Set.add("GyanSetu"); hash_Set.add("For"); hash_Set.add("GyanSetu"); hash_Set.add("Example"); hash_Set.add("Set"); System.out.print("Set output without the duplicates"); System.out.println(hash_Set); } } ``` ``` Set output without the duplicates[GyanSetu, Set, Example, For] ``` ### Basic Set operation : **Union**\ In this, we could simply add one Set with other. Since the Set will itself not allow any duplicate entries, we need not take care of the common values. **Expected Output:** ``` Union : [0, 1, 2, 3, 4, 5, 7, 8, 9] ``` \ **Intersection**\ We just need to retain the common values from both Sets. **Expected Output:** ``` Intersection : [0, 1, 3, 4] ``` \ **Difference**\ We just need to remove all the values of one Set from the other.\ \ **Expected Output:** ``` Difference : [2, 8, 9] ``` ```java // Java code for demonstrating union, intersection and difference // on Set import java.util.HashSet; import java.util.Set; public class SetExample { public static void main(String args[]) { Set a = new HashSet(); a.add(1); a.add(3); a.add(2); a.add(4); a.add(8); a.add(9); a.add(0); Set b = new HashSet(); b.add(1); b.add(3); b.add(7); b.add(5); b.add(4); b.add(0); b.add(7); a.add(5); // To find union Set union = new HashSet(a); union.addAll(b); System.out.print("Union of the two Set"); System.out.println(union); // To find intersection Set intersection = new HashSet(a); intersection.retainAll(b); System.out.print("Intersection of the two Set"); System.out.println(intersection); // To find the symmetric difference Set difference = new HashSet(a); difference.removeAll(b); System.out.print("Difference of the two Set"); System.out.println(difference); } } ``` ``` Union of the two Set[0, 1, 2, 3, 4, 5, 7, 8, 9] Intersection of the two Set[0, 1, 3, 4, 5] Difference of the two Set[2, 8, 9] ``` ### Problems: **1.** Write a Java program to append the specified element to the end of a hash set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-1.php) **2.** Write a Java program to iterate through all elements in a hash list. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-2.php) **3.** Write a Java program to get the number of elements in a hash set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-3.php) **4.** Write a Java program to empty an hash set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-4.php) **5.** Write a Java program to test a hash set is empty or not. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-5.php) **6.** Write a Java program to clone a hash set to another hash set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-6.php) **7.** Write a Java program to convert a hash set to an array. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-7.php) **8.** Write a Java program to convert a hash set to a tree set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-8.php) **9.** Write a Java program to convert a hash set to a List/ArrayList. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-9.php) **10.** Write a Java program to compare two hash set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-10.php) **11.** Write a Java program to compare two sets and retain elements which are same on both sets. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-11.php) **12.** Write a Java program to remove all of the elements from a hash set. [Go to the editor](https://www.w3resource.com/java-exercises/collection/index.php#editorr)\ [Click me to see the solution](https://www.w3resource.com/java-exercises/collection/java-collection-hash-set-exercise-12.php) ### CC: {% embed url="" %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://gyansetu-core-java-for-java.gitbook.io/project/collections-framework-part-2/sets.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. 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