Created
July 26, 2012 21:22
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Applicative Functor in Guava
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import com.google.common.base.Function; | |
import com.google.common.base.Optional; | |
import org.junit.Test; | |
import javax.annotation.Nullable; | |
import static org.fest.assertions.Assertions.assertThat; | |
public class OptionalTest { | |
@Test | |
public void should_() { | |
Optional<String> string = getSomething(true); | |
Optional<Optional<String>> result = Optional.of(string).transform(ID_FUNCTION).transform(FAIL_FUNCTION).transform(addString(" world!")); | |
assertThat(flatten(result).or("Fail")).isEqualTo("Fail"); | |
} | |
private static <T> Optional<T> flatten(Optional<Optional<T>> optional) { | |
if (optional.isPresent()) { | |
return optional.get(); | |
} | |
return Optional.absent(); | |
} | |
private Optional<String> getSomething(boolean b) { | |
return b ? Optional.of("Hello") : Optional.<String>absent(); | |
} | |
public static final Function<Optional<String>,Optional<String>> ID_FUNCTION = new Function<Optional<String>, Optional<String>>() { | |
@Override | |
public Optional<String> apply(@Nullable Optional<String> input) { | |
return input; | |
} | |
}; | |
public static final Function<Optional<String>,Optional<String>> FAIL_FUNCTION = new Function<Optional<String>, Optional<String>>() { | |
@Override | |
public Optional<String> apply(@Nullable Optional<String> input) { | |
return Optional.absent(); | |
} | |
}; | |
private Function<Optional<String>, Optional<String>> addString(final String value) { | |
return new Function<Optional<String>, Optional<String>>() { | |
@Override | |
public Optional<String> apply(@Nullable Optional<String> input) { | |
if (!input.isPresent()) { | |
return input; | |
} else { | |
return Optional.of(input.get() + value); | |
} | |
} | |
}; | |
} | |
} |
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