What is the difference between findFirst() and findAny() in Java8

Both findFirst() and findAny() are terminal operations in Java 8 streams that are used to find an element in a stream.

findFirst() returns the first element of the stream, while findAny() returns any element of the stream.

The difference between these two methods is important when working with parallel streams. In a sequential stream, there is no difference between the two methods because the first element and any element of the stream are the same. However, in a parallel stream, the behavior of findFirst() and findAny() can be different.

In a parallel stream, findFirst() will return the first element of the stream, which is the first element in the encounter order of the stream. This means that the first element in the stream may not be the first element processed in a parallel execution, but it will be the first element in the final encounter order of the stream.

On the other hand, findAny() returns any element of the stream, without any guarantee of which element will be returned in a parallel execution. In a parallel stream, findAny() will try to return the first element it finds, but it may not always be the first element in the encounter order of the stream.

Therefore, if the order of the elements is important and you want to guarantee the first element of the stream, use findFirst(). If the order of the elements is not important and you just need any element from the stream, use findAny().

Here are some examples of using findFirst() and findAny() methods in Java 8 streams: 


List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");

Optional<Stringgt firstElement = names.stream().findFirst();
System.out.println("First element: " + firstElement.get());

Optional<Stringgt anyElement = names.stream().findAny();
System.out.println("Any element: " + anyElement.get());

In this example, the findFirst() method is used to find the first element of the names list, which is "Alice". The findAny() method is also used to find any element of the names list, which may be "Alice", "Bob", "Charlie", or "David".

Here's another example that demonstrates the difference between findFirst() and findAny() in a parallel stream: 


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

Optional<Integergt firstElement = numbers.parallelStream().filter(n -> n % 2 == 0).findFirst();
System.out.println("First element: " + firstElement.get());

Optional<Integergt anyElement = numbers.parallelStream().filter(n -> n % 2 == 0).findAny();
System.out.println("Any element: " + anyElement.get());

In this example, the filter() method is used to create a new stream that contains only the even numbers from the numbers list. The findFirst() method is used to find the first even number in the stream, which may be 2, 4, or 6. The findAny() method is also used to find any even number in the stream, which may be 2, 4, or 6.

However, in a parallel execution, the result of findFirst() may be different from the first element in the encounter order of the stream, while findAny() may return any of the even numbers in the stream, without any guarantee of which one will be returned.

In this article, we have seen difference between findFirst() and findAny() with Examples