Fetch first element of stream matching the criteria

Cracking the filtering and extraction code

Pairing the filter() and findFirst() methods means we can execute lambda expressions that describe intricate criteria, all in a few lines of expressive, compact code.

Method references and lambda magic

The filter() function takes on a predicate as its argument—a lambda expression that sets out the selection conditions. For elemental criteria, method references are the cleaner choice:

Stream.of("apple", "banana", "cherry")
      .filter("banana"::equals)
      .findFirst()
      .ifPresent(System.out::println); // "banana splats onto the console"
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For null proof code and rigorous equality checks, gear up with Objects::equals in your filter function:

Stream.of("apple", null, "cherry")
      .filter(Objects::nonNull) // Nulls, need not apply!
      .filter(fruit -> Objects.equals(fruit, "banana"))
      .findFirst()
      .ifPresent(System.out::println); // "banana" makes its star appearance


For lambda expressions, note that syntax can vary : parentheses around a single parameter could be optional, which helps maintain brevity. But the semantics takes precedence.

Handling the ghosts : empty and null elements

When faced with streams which could contain phantom null values or no matching elements at all, it's imperative to code for null safety and gracious failure:

Stream.of("apple", null, "cherry")
      .filter(Objects::nonNull) // Nulls are JOptionPane.showMessageDialog'ed
      .filter(fruit -> fruit.contains("b"))
      .findFirst()
      .orElseThrow(() -> new NoSuchElementException("Missing fruit behind the error")); // Custom exception informs you nicely


Stream order and the pandemonium

For streams sourced from collections with no defined order like a HashSet, searching for a "first" element is a shot in the dark. So, for deterministic searching, consider sorting the stream:

new HashSet<>(Arrays.asList("apple", "banana", "cherry")).stream()
      .sorted() // The fruits are practicing social distancing
      .filter(fruit -> fruit.startsWith("a"))
      .findFirst()
      .ifPresent(System.out::println); // "apple" pops out first


More power to stream operations

For utmost efficiency, chain those stream methods. Lambda expressions can keep your code short and sweet, and type inference often comes to our rescue to slim things down further.

Remember, filter() is about matching criteria, while map() serves for transforming elements. Mixing them up is a no-no. Keep your lambda argument types in step with the expected filter method signature.

Edge cases and oddballs

• When dealing with streams garnered from collections with no defined iteration order (like HashSet), orderly matters.
• Mind the concurrency: For parallel streams, using findFirst() may be counterproductive; findAny() may offer faster results.
• Performance is key: For data-intensive operations, fine-tuning the filter() predicate for optimal efficiency is crucial.

Day to day practical insights

Code style and best practices

• Lean towards method references as opposed to lambda when feasible.
• Frequent usage of package-specific utility methods like String::isEmpty simplifies common checks in filter().
• Make the most of your Optionals: Implement orElseGet, orElse, and orElseThrow in accordance with your null-handling strategy.

Common pitfalls

• Do not overuse Optionals. They indeed help, but bring along additional complexity and can be an overkill for simple checks.
• Be warned that findFirst() does not necessarily ensure delivering the "first" element for unordered streams.