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Sequences

Supported fake sequences:

  • FakeCollection
  • FakeStream

FakeSequence API

Support of fake collections has been added to Datafaker since version 1.2.0.
Support of fake streams/fake sequence has been added to Datafaker since version 1.7.0.

For example, the following code will generate a list/stream of first and last names with number of elements in it between 3 and 5:

List<String> names = 
    faker.collection(
            () -> faker.name().firstName(), 
            () -> faker.name().lastName())
        .len(3, 5)
        .generate();

Stream<String> names = 
    faker.stream(
            () -> faker.name().firstName(), 
            () -> faker.name().lastName())
        .len(3, 5)
        .generate();

A list/stream can also contain different types:

List<Object> objects =
    faker.<Object>collection(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .maxLen(5)
        .generate();

Stream<Object> objects =
    faker.<Object>stream(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .maxLen(5)
        .generate();

With usage of nullRate it is possible to specify how often it should contain null values. By default, it's value is 0, i.e. no null values will be generated.

List<Object> objects =
    faker.<Object>collection(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .nullRate(1)
        .maxLen(5)
        .generate();

Stream<Object> objects =
    faker.<Object>stream(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .nullRate(1)
        .maxLen(5)
        .generate();

The above will generate a collection/stream where every value is null. To generate a collection/stream with only about 30% values of null, nullRate(0.3) will do it.

List<Object> objects =
    faker.<Object>collection(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .nullRate(0.3)
        .maxLen(5)
        .generate();

Stream<Object> objects =
    faker.<Object>stream(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .nullRate(0.3)
        .maxLen(5)
        .generate();

FakeSequence also supports generation of an infinite stream:

Stream<Object> objects =
    faker.<Object>stream(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .generate();

It is also possible to distinguish finite and infinite FakeStreams based on FakeSequence API:

FakeSequence<Object> fakeSequence = faker.<Object>stream(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .build();

System.out.println(fakeSequence.isInfinite()); // true

For FakeCollection this function will always return false:

FakeSequence<Object> fakeSequence = faker.<Object>collection(
            () -> faker.name().firstName(),
            () -> faker.random().nextInt(100))
        .build();

System.out.println(fakeSequence.isInfinite()); // false
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