How do I use the filter operation in Java Streams API?

How do I use the filter operation in Java Streams API?

The filter operation in Java Streams API allows you to filter elements based on a given predicate. You can use it to create a new stream that contains only the elements that match the condition.

Can you give me an example of using filter with a list of integers?

Sure! Here's an example:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
List<Integer> evenNumbers = numbers.stream()
    .filter(n -> n % 2 == 0)
    .collect(Collectors.toList());

This will give you a list of even numbers: [2, 4, 6].

What if I want to filter a list of strings?

You can use the filter operation similarly. For example:

List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
List<String> filteredNames = names.stream()
    .filter(name -> name.startsWith("A"))
    .collect(Collectors.toList());

This will return a list containing only "Alice".

Are there any performance considerations when using filter?

Yes, using filter can impact performance, especially with large datasets. It's important to consider the complexity of the predicate and the size of the stream.