Stream filter() method in Java8 with examples

In Java, the filter() method is part of the Stream API and is used to filter elements from a stream based on a specified condition. The filter() method returns a new stream that contains only the elements that satisfy the specified condition

Table of Content :

Here's the syntax for using the filter() method in Java: 


 
 Stream<Tgt filter(Predicate<? super T> predicate)

where T is the type of the elements in the stream, and predicate is a Predicate functional interface that is used to test each element in the stream. The Predicate functional interface takes an element of type T as input and returns a boolean value indicating whether the element satisfies the specified condition.

Here's an example usage of the filter() method in Java:

Using the Boolean.toString() method: 


 
List<Integergt numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

Stream<Integergt evenNumbers = numbers.stream().filter(num -> num % 2 == 0);

evenNumbers.forEach(System.out::println); // prints 2 4 6 8 10

Stream filter() and collect() method examples:

Let's say we have a list of names and we want to filter out only the names that start with the letter "J" and store them in a new list. We can use the filter() method to filter out the elements that match our condition, and then use the collect() method to collect the filtered elements into a new list. 


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

public class FilterAndCollectExample {
	public static void main(String[] args) {
		List<String> names = Arrays.asList("Jones", "Jara", "John", "Jane", "Mary", "Jack");

		List<Stringgt names1 = names.stream().filter(name -> name.startsWith("J")).
				collect(Collectors.toList());

		System.out.println(names1); // [Jones, Jara, John, Jane, Jack]
	}
}

Stream filter() and map() method to find even numbers and Square them 


 
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class StreamFilterAndMapMethod {
 
    public static void main(String[] args) {
 
        System.out.println("Filter out the even numbers and find Square for them : \n");
 
        List<Integergt numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
 
        List<Integergt newList = numbers
                .stream()  
                .filter(i -> i%2 != 0)  
                .map(n -> n * n )  
                .collect(Collectors.toList());  
 
        newList.forEach(s -> System.out.println(s));
        
       
    }
}

output:

Filter out the even numbers and find Square for them : 

1
9
25
49
81

Find duplicates in given String list Using filter


 

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

public class FindDuplicatesUsingFilterAndSetAddMethod {
	public static void main(String[] args) {
		List<Stringgt companies = new ArrayList();
	 
        companies.add("Facebook");
        companies.add("Flipkart");
        companies.add("Walmart");
        companies.add("Jio");
        companies.add("Airtel");
        companies.add("Idea");  
        companies.add("HDFC");
        companies.add("Jio");
        companies.add("Flipkart");
        
       Set<Stringgt distinctCompanies  = new HashSet();
      
       Set<Stringgt duplicates =   companies.stream().filter(company-> !distinctCompanies .add(company))
       .collect(Collectors.toSet());
       
       System.out.println(duplicates);
        
	}
}

In this Article we have seen what is filter in java Stream API with examples