Java 8 Stream findFirst() vs. findAny() – Java 8 Stream findFirst() vs. findAny()

最后修改: 2017年 1月 22日


1. Overview


The Java 8 Stream API introduced two methods that are often misunderstood: findAny() and findFirst().

Java 8 Stream API引入了两个经常被误解的方法。findAny()/em>和findFirst()/em>。

In this quick tutorial, we’ll look at the difference between these two methods and when to use them.


2. Using Stream.findAny()

2.使用 Stream.findAny()

As the name suggests, the findAny() method allows us to find any element from a Stream. We use it when we’re looking for an element without paying an attention to the encounter order:


The method returns an Optional instance, which is empty if the Stream is empty:


public void createStream_whenFindAnyResultIsPresent_thenCorrect() {
    List<String> list = Arrays.asList("A","B","C","D");

    Optional<String> result =;

    assertThat(result.get(), anyOf(is("A"), is("B"), is("C"), is("D")));

In a non-parallel operation, it will most likely return the first element in the Stream, but there is no guarantee for this.


For maximum performance when processing the parallel operation, the result cannot be reliably determined:


public void createParallelStream_whenFindAnyResultIsPresent_thenCorrect()() {
    List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
    Optional<Integer> result = list
      .filter(num -> num < 4).findAny();

    assertThat(result.get(), anyOf(is(1), is(2), is(3)));

3. Using Stream.findFirst()

3.使用 Stream.findFirst()

The findFirst() method finds the first element in a Stream. So, we use this method when we specifically want the first element from a sequence.


When there is no encounter order, it returns any element from the Stream. According to the java.util.streams package documentation, “Streams may or may not have a defined encounter order. It depends on the source and the intermediate operations.”

当没有相遇顺序时,它会返回Stream中的任何元素。根据 java.util.streams包的文档,”流可能有也可能没有定义的相遇顺序。这取决于源和中间操作”。

The return type is also an Optional instance, which is empty if the Stream is empty too:


public void createStream_whenFindFirstResultIsPresent_thenCorrect() {

    List<String> list = Arrays.asList("A", "B", "C", "D");

    Optional<String> result =;

    assertThat(result.get(), is("A"));

The behavior of the findFirst method does not change in the parallel scenario. If the encounter order exists, it will always behave deterministically.


4. Conclusion


In this article, we looked at the findAny() and findFirst() methods of the Java 8 Streams API.

在这篇文章中,我们研究了Java 8 Streams API的findAny() findFirst()方法。

The findAny() method returns any element from a Stream, while the findFirst() method returns the first element in a Stream.


The complete source code and all code snippets for this article are over on GitHub.