No, filter does not scan the whole stream. It's an intermediate operation, which returns a lazy stream (actually all intermediate operations return a lazy stream). To convince you, you can simply do the following test:
List<Integer> list = Arrays.asList(1, 10, 3, 7, 5);
int a = list.stream()
.peek(num -> System.out.println("will filter " + num))
.filter(x -> x > 5)
.findFirst()
.get();
System.out.println(a);
Which outputs:
will filter 1
will filter 10
10
You see that only the two first elements of the stream are actually processed.
So you can go with your approach which is perfectly fine.
Answer from Alex on Stack Overflow Top answer 1 of 9
952
No, filter does not scan the whole stream. It's an intermediate operation, which returns a lazy stream (actually all intermediate operations return a lazy stream). To convince you, you can simply do the following test:
List<Integer> list = Arrays.asList(1, 10, 3, 7, 5);
int a = list.stream()
.peek(num -> System.out.println("will filter " + num))
.filter(x -> x > 5)
.findFirst()
.get();
System.out.println(a);
Which outputs:
will filter 1
will filter 10
10
You see that only the two first elements of the stream are actually processed.
So you can go with your approach which is perfectly fine.
2 of 9
132
However this seems inefficient to me, as the filter will scan the whole list
No it won't - it will "break" as soon as the first element satisfying the predicate is found. You can read more about laziness in the stream package javadoc, in particular (emphasis mine):
Many stream operations, such as filtering, mapping, or duplicate removal, can be implemented lazily, exposing opportunities for optimization. For example, "find the first String with three consecutive vowels" need not examine all the input strings. Stream operations are divided into intermediate (Stream-producing) operations and terminal (value- or side-effect-producing) operations. Intermediate operations are always lazy.
Medium
rameshfadatare.medium.com › java-stream-findfirst-method-with-examples-2988f89becc2
Java Stream findFirst() Method with Examples | by Ramesh Fadatare | Medium
September 27, 2024 - import java.util.Optional; import ... Stream<String> stream = Stream.of("apple", "banana", "cherry"); // Use findFirst() to retrieve the first element from the stream Optional<String> firstElement = stream.findFirst(); // Print the ...
Stream filter findFirst
Streams, and their equivalents in other languages, are usually lazy. So nothing is really done in the intermediate steps, like map and filter. It's not until the terminal operation, findFirst(), is executed that work is done, the intermediate steps are just defining what you want to do. You can see this by executing Stream.of(1, 2, 3, 4, 5, 6) .map(i -> { System.out.println(i); return i * 2; }) .findFirst(); It will print only one line with «1» More on reddit.com
11
4
October 27, 2015Java 8 functional alternative to for loop break
The filter() method (from the Stream interface) along with the findFirst() method would solve your need. More on reddit.com
6
7
March 6, 2015Java67
java67.com › 2018 › 03 › java-8-stream-find-first-and-filter-example.html
Java 8 Stream filter() + findFirst Example Tutorial | Java67
It's also lazy which means it will not do anything until you call a terminal method like findFirst(). You can further see Learn Java Functional Programming with Lambdas and Stream course by Ranga Karnam to learn more about Stream features. Here is the code to find the first element from a List in Java 8 after applying a predicate: import java.util.Arrays; import java.util.List; /** * * A simple example find the first element from * List based upon condition.
Baeldung
baeldung.com › home › java › java streams › java stream findfirst() vs. findany()
Java Stream findFirst() vs. findAny() | Baeldung
January 9, 2024 - The Java 8 Stream API introduced ... and findFirst(). In this quick tutorial, we’ll look at the difference between these two methods and when to use them. A quick and practical guide to filtering Streams of Optionals in Java 8 and Java 9 ... A quick and practical guide to using Java 8 Streams with primitive ...
HowToDoInJava
howtodoinjava.com › home › java 8 › java stream findfirst() example
Java Stream findFirst() Example
May 27, 2024 - If Stream has defined encounter order, the findFirst() returns first element in encounter order.
Medium
medium.com › @Mohd_Aamir_17 › exploring-anymatch-and-findfirst-in-java-8-streams-with-examples-63a7c54d5e9f
Exploring anyMatch and findFirst in Java 8 Streams with Examples | by Mohd Aamir | Medium
September 5, 2024 - The findFirst() method is especially useful when: You need to get the first matching element based on a certain condition. You’re working with ordered streams where the first element carries significance.
Scaler
scaler.com › topics › java-stream-findfirst
Java Stream findFirst() - Scaler Topics
Scaler Topics offers free certificate courses for all programming languages like Java, Python, C, C++, DSA etc. Learn from top MAANG experts and level up your skills. Explore now
GeeksforGeeks
geeksforgeeks.org › java › stream-findfirst-java-examples
Stream findFirst() in Java with examples - GeeksforGeeks
December 26, 2025 - ... Parameters: This method does not take any parameters. Return Value: Returns an Optional<T> containing the first element of the stream and returns an empty Optional if the stream is empty.
Blogger
javarevisited.blogspot.com › 2016 › 03 › how-to-find-first-element-of-stream-in.html
How to find the first element in Stream in Java 8? findFirst() Example
October 5, 2024 - One of the important things to know while using for writing such logic is that all intermediate operations e.g. filter(), map(), etc are lazy and they are only executed when a terminal operation like findFirst() or forEach() is called. This also means, a lot of opportunities for optimization depending upon the size of the original list. In this article, I'll show you a couple of examples of the findFirst() method with Predicate to show the true power of Stream in Java 8.
Mkyong
mkyong.com › home › java8 › java 8 stream findfirst() and findany()
Java 8 Stream findFirst() and findAny() - Mkyong.com
February 8, 2020 - package com.mkyong.java8; import java.util.Arrays; import java.util.List; import java.util.Optional; public class Java8FindFirstExample1 { public static void main(String[] args) { List<Integer> list = Arrays.asList(1, 2, 3, 2, 1); Optional<Integer> first = list.stream().findFirst(); if (first.isPresent()) { Integer result = first.get(); System.out.println(result); // 1 } else { System.out.println("no value?"); } Optional<Integer> first2 = list .stream() .filter(x -> x > 1).findFirst(); if (first2.isPresent()) { System.out.println(first2.get()); // 2 } else { System.out.println("no value?"); } } }
TutorialsPoint
tutorialspoint.com › find-the-first-element-of-a-stream-in-java
Find the first element of a Stream in Java
July 31, 2023 - Apply a filter to the stream to match the desired condition. Use the findFirst method to obtain an Optional object with the first matching element. Check if the Optional object is empty or contains a value.
W3Docs
w3docs.com › java
Find first element by predicate
Java · Find first element by predicate ... the element should satisfy. Finally, you can use the findFirst() method to get the first element in the stream that matches the condition, or findAny() if you don't care which element you ...
Stack Abuse
stackabuse.com › java-8-streams-guide-to-findfirst-and-findany
Java 8 Streams: Definitive Guide to findFirst() and findAny()
November 28, 2021 - The findFirst() method returns the first element of a stream or an empty Optional. If the stream has no encounter order, any element is returned, as it's ambiguous which is the first one anyway. The findAny() method returns any element of the stream - much like findFirst() with no encounter order.
Baeldung
baeldung.com › home › java › java collections › get index of first element matching boolean using java streams
Get Index of First Element Matching Boolean Using Java Streams | Baeldung
March 7, 2025 - Learn how to use the Java Stream API and third-party libraries to find the index of the first element in a List that matches a boolean condition.
nipafx
nipafx.dev › java-stream-findfirst-findany-reduce
Beware Of findFirst() And findAny() - nipafx.dev
January 14, 2016 - Stream.findFirst() and findAny() work with any number of elements in the stream. Make sure to reduce(toOnlyElement()) if there should be at most one.
Jsparrow
jsparrow.github.io › rules › enhanced-for-loop-to-stream-find-first.html
Replace For-Loop with Stream::findFirst | jSparrow Documentation
List<String> values = generateList(input); String key = values.stream() .filter(value -> value.length() > 4) .findFirst() .orElse("");
TWpower's Tech Blog
twpower.github.io › 328-difference-between-get-and-findfirst-in-java-list-en
[Java](EN) Difference between get(0) and findFirst() in ...
November 19, 2023 - Return the first element that meets the given condition and if there is no element satisfying that condition then return Optional.empty() Available after Java 8 · List<String> myList = Arrays.asList("1", "2", "3"); Optional<String> ...
Dirask
dirask.com › posts › Java-8-find-first-element-in-Stream-that-matches-criteria-10QVOD
Java 8 - find first element in Stream that matches criteria
import java.util.*; public class Example { public static void main(String[] args) { // create list of strings List<String> letters = Arrays.asList("A1", "B1", "A2", "B2"); // find first element that matches the criteria String result = letters.stream() .filter(x -> x.startsWith("B")) // <----- example criteria .findFirst() .orElse(null); System.out.println(result); // B1 } }
Reddit
reddit.com › r/java › stream filter findfirst
r/java on Reddit: Stream filter findFirst
October 27, 2015 -
I'm curious about the execution of filtering a stream and calling findFirst. Does the filter get applied to the whole list and then the first element is found from the filtered list? Or does the findFirst get applied during the filter, grabbing the first element matching the filter and prevent iterating through every element?
I've been having trouble wording that in a way that Google or this sub would tell me, so I apologize if this has been discussed before.
Top answer 1 of 4
2
Streams, and their equivalents in other languages, are usually lazy. So nothing is really done in the intermediate steps, like map and filter. It's not until the terminal operation, findFirst(), is executed that work is done, the intermediate steps are just defining what you want to do. You can see this by executing Stream.of(1, 2, 3, 4, 5, 6) .map(i -> { System.out.println(i); return i * 2; }) .findFirst(); It will print only one line with «1»
2 of 4
2
This stream execution might answer your questions: Stream.of(1, 2, 3, 4, 5, 6) .peek(v -> System.out.println("Peeking 1: " + v)) .filter(v -> v % 2 == 0) .peek(v -> System.out.println("Peeking 2: " + v)) .findFirst() .ifPresent(v -> System.out.println("First : " + v)); It yields Peeking 1: 1 Peeking 1: 2 Peeking 2: 2 First : 2 As you can see, findFirst() pulls values out of the Stream only until it finds the first value produced by the previous operations. This Stack Overflow question also explains this in more detail.
Javatpoint
javatpoint.com › stream-findfirst-method-in-java
Stream findFirst() Method in Java - Javatpoint
Stream findFirst() Method in Java with java tutorial, features, history, variables, programs, operators, oops concept, array, string, map, math, methods, examples etc.