How to Implement `takeWhile` in Java 8 Streams?

How to Limit a Stream Until a Predicate Fails

Java 8 streams provide a powerful set of operations for manipulating and processing data. Among these operations is a need to limit a stream until the first element fails to match a given predicate. This question explores how to achieve this functionality in Java 8.

In Java 9, the takeWhile operation was introduced, which can be used to limit a stream based on a predicate. However, for Java 8, we need to find an alternative solution.

Solution

To implement takeWhile in Java 8, we can use the following approach:

• Create an iterate stream that generates a sequence of elements indefinitely.
• Use filter to create a stream that includes only the elements that match the predicate.
• Use limit to set the maximum number of elements in the resulting stream.

Here's an example code:

IntStream
    .iterate(1, n -> n + 1)
    .filter(n -> n < 10)
    .limit(-1)
    .forEach(System.out::println);

In JDK 9, the takeWhile operation can be used directly, as shown in the following example:

IntStream
    .iterate(1, n -> n + 1)
    .takeWhile(n -> n < 10)
    .forEach(System.out::println);

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