Find the Intersect from the two list using Java 8

April 05, 2026

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Today I have released new video on "Find the Intersect from the two list using Java 8"

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Find the Intersect from the two list using Java 8

package org.practice.basicprgms;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

public class FindIntersectionList {

	public static void main(String[] args) {
		List<Integer> list1 = Arrays.asList(1,2,3,4,5);
		List<Integer> list2 = Arrays.asList(3,4,5,6,7); 
		List<Integer> intersectList = new ArrayList<>();
				
		// 1. Using filter() and Contains method		
		intersectList =
			list1.stream()
				.filter(list2::contains)
				.collect(Collectors.toList());
		System.out.println("Using filter() and Contains method "+ intersectList);
		
		// 2. Using Set 
		Set<Integer> intersectSet = new HashSet<>(list2);
		intersectList =
				list1.stream()
					.filter(intersectSet::contains)
					.collect(Collectors.toList());
		System.out.println("Using Set  "+ intersectList);
		
		
		// 3. Using Collections.frequency()
		intersectList =
			list1.stream()
				.filter(e -> Collections.frequency(list2, e) > 0)
				.collect(Collectors.toList());
		System.out.println("Using Collections.frequency()  "+ intersectList);
		
		// 4. Using flatMap
		intersectList =
			list1.stream()
				.flatMap(e -> list2.stream().filter(e::equals))
				.collect(Collectors.toList());
		System.out.println("Using flatMap  "+ intersectList);
		

		// 5. Using Distinct() avoid duplicates
		intersectList = 
			list1.stream()
				.filter(list2::contains)
				.distinct()
				.collect(Collectors.toList());
		System.out.println("Using Distinct() avoid duplicates  "+ intersectList);

		// 6. Using retainall traditional method
		List<Integer> dupList = new ArrayList<>(list1);
		dupList.retainAll(list2);
		System.out.println("Using retainall traditional method  "+ dupList);

		// 7. Using Set Intersection
		Set<Integer> set1 = new HashSet<>(list1);
		Set<Integer> set2 = new HashSet<>(list2);
		
		set1.retainAll(set2);
		System.out.println("Using Set Intersection  "+ set1);
		
		// 8. Using foreach
		for(int i : list1)
			if(list2.contains(i) && !intersectList.contains(i))
				intersectList.add(i);
		System.out.println("Using foreach  "+ intersectList);

	}

}