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Java Program to Calculate the Intersection of two Sets
What is a Set in Java ?
In Java, a Set is a collection that cannot contain duplicate elements. It is an interface in the Java Collection Framework, and has several implementing classes such as HashSet, TreeSet, and LinkedHashSet.
A Set can be useful when you need to store a collection of unique items and perform operations such as testing for membership, adding or removing elements, or iterating through the elements.
What is Set Intersection ?
In set theory, the intersection of two sets is a new set that contains only the elements that are present in both of the original sets. It is denoted by the symbol ∩.
In Java, the retainAll() method of the Set interface can be used to perform the intersection of two sets. The retainAll() method modifies the current set so that it only contains elements that are also contained in a specified collection.
Example 1 : Calculation of Intersection using retainAll() Method :
import java.util.HashSet;
import java.util.Set;
public class Main {
public static void main(String[] args) {
Set <String> setA = new HashSet<>();
setA.add("apple");
setA.add("banana");
setA.add("orange");
Set <String> setB = new HashSet<>();
setB.add("banana");
setB.add("kiwi");
setB.add("orange");
setA.retainAll(setB);
System.out.println("Intersection of setA and setB: " + setA);
}
}
Output :
Intersection of setA and setB: [banana, orange]
Example 2 : Calculation of Intersection using retainAll() Method :
import java.util.HashSet;
import java.util.Set;
public class Main {
public static void main(String[] args) {
//Declaration of set1
Set <String> set1 = new HashSet();
//Adding elements to set1
set1.add("Red");
set1.add("Green");
set1.add("Black");
set1.add("White");
set1.add("Pink");
System.out.println("Set1: " + set1);
//Declaration of set2
Set <String> set2 = new HashSet();
//Adding elements in set2
set2.add("Red");
set2.add("Green");
set2.add("Black");
set2.add("Pink");
System.out.println("Set2: " + set2);
set1.retainAll(set2);
System.out.println("Intersection of two sets: " + set1);
}
}
Output :
Set1: [Red, White, Pink, Black, Green] Set2: [Red, Pink, Black, Green] Intersection of two sets: [Red, Pink, Black, Green]
Then, it uses the retainAll() method, which modifies the first set (set1) to keep only the elements that are also in the second set (set2). The method retainAll() modifies the first set, it is a in-place operation, so in the end, the first set contains only the intersection of the two sets.
Then it prints the first set after modification, which will be the intersection of the two sets.
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