CODEWITHSUNDEEP
javaarrayslambdajava-8java-stream
Joe Almore
Joe Almore

Reputation: 4331

Java - Find Element in Array using Condition and Lambda

In short, I have this code, and I'd like to get an specific element of the array using a condition and lambda. The code would be something like this:

Preset[] presets = presetDALC.getList();
Preset preset = Arrays.stream(presets).select(x -> x.getName().equals("MyString"));

But obviously this does not work. In C# would be something similar but in Java, how do I do this?

Upvotes: 41

Views: 134110

Answers (4)

Akash Thakare
Akash Thakare

Reputation: 22972

You can do it like this,

Optional<Preset> optional = Arrays.stream(presets)
                                  .filter(x -> "MyString".equals(x.getName()))
                                  .findFirst();

// Check whether optional has element you are looking for
if (optional.isPresent()) {
    Preset p = optional.get(); // Get it from optional
}

You can read more about Optional here.

Upvotes: 72

epox
epox

Reputation: 10900

One-liner since Java 8:

Preset found = Stream.of(presets)
    .filter(p -> p.getName().equals("MyString"))
    .findFirst().orElseThrow();

Avoid declaring Optional<>, that returned from findFirst as a variable or a parameter. It is designed for return types / "one-liner" styles.

Upvotes: 0

Robby Cornelissen
Robby Cornelissen

Reputation: 97150

Like this:

Optional<Preset> preset = Arrays
        .stream(presets)
        .filter(x -> x.getName().equals("MyString"))
        .findFirst();

This will return an Optional which might or might not contain a value. If you want to get rid of the Optional altogether:

Preset preset = Arrays
        .stream(presets)
        .filter(x -> x.getName().equals("MyString"))
        .findFirst()
        .orElse(null);

The filter() operation is an intermediate operation which returns a lazy stream, so there's no need to worry about the entire array being filtered even after a match is encountered.

Upvotes: 35

Andreas
Andreas

Reputation: 159096

Do you want first matching, or all matching?

String[] presets = {"A", "B", "C", "D", "CA"};

// Find all matching
List<String> resultList = Arrays.stream(presets)
                                .filter(x -> x.startsWith("C"))
                                .collect(Collectors.toList());
System.out.println(resultList);

// Find first matching
String firstResult = Arrays.stream(presets)
                           .filter(x -> x.startsWith("C"))
                           .findFirst()
                           .orElse(null);
System.out.println(firstResult);

Output

[C, CA]
C

Upvotes: 12

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