How To Filter List Using Java Stream API?

Introduction

Stream API feature was introduced in Java 8 but it is still confusing for many and also many have not even used it a single time. I will try to explain Java Stream concepts with simple examples in Learn Stream API in Java with Examples series.

In this post, we will learn to filter a Java List using Stream APIs i.e. filter() method.

YouTube Tutorials

If you want to learn from a video tutorial then please refer to the below video –

Filter Java List List Without Stream API

We may be required to filter a Java List based on one or multiple conditions. We need to iterate the array and apply filter conditions. Let’s write a very simple program to filter a list.

Java Program

package solveproblemswithsreams;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class FilterListUsingJavaStreamAPI {
        
        public static void main(String[] args) {
                
                List allSubjets = Arrays.asList("Java","Functional Testing", "Performace Testing", "Selenium Testing", "Mongo DB");
                List allTestingSubjects = new ArrayList<>();
                // Iterating the list
                for(String ele : allSubjets)
                {
                        // filter condition
                        if(ele.contains("Testing"))
                                allTestingSubjects.add(ele);    
                }
                
                System.out.println("All subjects : "+ allSubjets);
                System.out.println("All testing subjects : "+ allTestingSubjects);
        }

}

Output

All subjects : [Java, Functional Testing, Performace Testing, Selenium Testing, Mongo DB]
All testing subjects : [Functional Testing, Performace Testing, Selenium Testing]

Filter Java List List With Stream API

Stream interface provides a method filter() which helps you to filter a list based on condition/s. The filter() method takes a Predicate which is a functional interface. We can use the lambda expressions to write shorter code.

1. Get a sequential stream of List using stream() method.
2. Call filter() method with the condition on stream.
3. Collect results into a List.

Java Program

package solveproblemswithsreams;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class FilterListUsingJavaStreamAPI {
        
        public static void main(String[] args) {
                
                List allSubjets = Arrays.asList("Java","Functional Testing", "Performace Testing", "Selenium Testing", "Mongo DB");
                List allTestingSubjects = new ArrayList<>();
                
                allTestingSubjects = 
                allSubjets
                        .stream()
                        .filter(ele -> ele.contains("Testing"))
                        .collect(Collectors.toList());
                        
                System.out.println("All subjects : "+ allSubjets);
                System.out.println("All testing subjects : "+ allTestingSubjects);
        }
}

Output

All subjects : [Java, Functional Testing, Performace Testing, Selenium Testing, Mongo DB]
All testing subjects : [Functional Testing, Performace Testing, Selenium Testing]

You can use multiple conditions as below –

.filter(ele -> ele.contains(“Testing”) && ele.contains(“Selenium”))

GitHub Repo Link

https://github.com/amod-mahajan/MSE_LearnJavaStreamsWithExamples.git

If you have any doubt, feel free to comment below.
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