本文整理了Java中com.annimon.stream.Optional.empty()方法的一些代码示例，展示了Optional.empty()的具体用法。这些代码示例主要来源于Github/Stackoverflow/Maven等平台，是从一些精选项目中提取出来的代码，具有较强的参考意义，能在一定程度帮忙到你。Optional.empty()方法的具体详情如下：
包路径：com.annimon.stream.Optional
类名称：Optional
方法名：empty

Optional.empty介绍

[英]Returns an empty Optional.
[中]返回一个空的可选值。

代码示例

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Override
  public Optional<Integer> get() {
    return Optional.empty();
  }
});

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

/**
 * Performs filtering on inner value if it is present.
 *
 * @param predicate  a predicate function
 * @return this {@code Optional} if the value is present and matches predicate,
 *              otherwise an empty {@code Optional}
 */
public Optional<T> filter(Predicate<? super T> predicate) {
  if (!isPresent()) return this;
  return predicate.test(value) ? this : Optional.<T>empty();
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

/**
 * Invokes the given mapping function on inner value if present.
 *
 * @param <U> the type of result value
 * @param mapper  mapping function
 * @return an {@code Optional} with transformed value if present,
 *         otherwise an empty {@code Optional}
 * @throws NullPointerException if value is present and
 *         {@code mapper} is {@code null}
 */
public <U> Optional<U> map(Function<? super T, ? extends U> mapper) {
  if (!isPresent()) return empty();
  return Optional.ofNullable(mapper.apply(value));
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test(expected = RuntimeException.class)
public void testIfPresentOrElseWhenValueAbsentAndConsumerNull() {
  Optional.<Integer>empty().ifPresentOrElse(null, new Runnable() {
    @Override
    public void run() {
      throw new RuntimeException();
    }
  });
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test(expected = ArithmeticException.class)
public void testOrElseThrow() {
  Optional.empty().orElseThrow(new Supplier<RuntimeException>() {
    @Override
    public RuntimeException get() {
      return new ArithmeticException();
    }
  });
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testExecuteIfPresentOnAbsentValue() {
  Optional.<Integer>empty()
      .executeIfPresent(new Consumer<Integer>() {
        @Override
        public void accept(Integer value) {
          fail();
        }
      });
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test(expected = RuntimeException.class)
public void testExecuteIfAbsent() {
  Optional.empty()
      .executeIfAbsent(new Runnable() {
        @Override
        public void run() {
          throw new RuntimeException();
        }
      });
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testCustomTerminal() {
  Integer result = Optional.<Integer>empty()
      .custom(new Function<Optional<Integer>, Integer>() {
        @Override
        public Integer apply(Optional<Integer> optional) {
          return optional.orElse(0);
        }
      });
  assertThat(result, is(0));
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testOrElseGet() {
  int value = Optional.<Integer>empty().orElseGet(new Supplier<Integer>() {
    @Override
    public Integer get() {
      return 42;
    }
  });
  assertEquals(42, value);
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testToStringOnEmptyOptional() {
  assertEquals("Optional.empty", Optional.empty().toString());
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testStreamOnEmptyOptional() {
  long count = Optional.empty().stream().count();
  assertThat(count, is(0L));
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testEqualsWithTwoEmptyOptional() {
  final Optional<Integer> empty1 = Optional.ofNullable(null);
  final Optional<Integer> empty2 = Optional.empty();
  assertEquals(empty1, empty2);
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testOrOnEmptyOptionalAndEmptySupplierOptional() {
  final Optional<Integer> optional = Optional.<Integer>empty().or(new Supplier<Optional<Integer>>() {
    @Override
    public Optional<Integer> get() {
      return Optional.empty();
    }
  });
  assertThat(optional, isEmpty());
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testSelectOnEmptyOptional() {
  Optional<Integer> result = Optional.empty()
      .select(Integer.class);
  assertThat(result, isEmpty());
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testOrOnEmptyOptional() {
  int value = Optional.<Integer>empty().or(new Supplier<Optional<Integer>>() {
    @Override
    public Optional<Integer> get() {
      return Optional.of(19);
    }
  }).get();
  assertEquals(19, value);
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testIsEmpty() {
  Optional<Integer> optional = Optional.empty();
  assertThat(optional, isEmpty());
  assertThat(optional, not(isPresent()));
  assertThat(isEmpty(), description(is("Optional value should be empty")));
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testHashCodeWithTwoEmptyOptional() {
  final Optional<Integer> empty1 = Optional.ofNullable(null);
  final Optional<Integer> empty2 = Optional.empty();
  assertEquals(empty1.hashCode(), empty2.hashCode());
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@Test
public void testMapOnEmptyOptional() {
  assertFalse(
      Optional.<Integer>empty()
          .map(UnaryOperator.Util.<Integer>identity())
          .isPresent());
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@SuppressWarnings("EqualsBetweenInconvertibleTypes")
@Test
public void testEquals() {
  assertEquals(OptionalLong.empty(), OptionalLong.empty());
  assertNotEquals(OptionalLong.empty(), Optional.empty());
  assertEquals(OptionalLong.of(42), OptionalLong.of(42));
  assertNotEquals(OptionalLong.of(41), OptionalLong.of(42));
  assertNotEquals(OptionalLong.of(0), OptionalLong.empty());
}

代码示例来源：origin: aNNiMON/Lightweight-Stream-API

@SuppressWarnings("EqualsBetweenInconvertibleTypes")
@Test
public void testEquals() {
  assertEquals(OptionalInt.empty(), OptionalInt.empty());
  assertNotEquals(OptionalInt.empty(), Optional.empty());
  assertEquals(OptionalInt.of(42), OptionalInt.of(42));
  assertNotEquals(OptionalInt.of(41), OptionalInt.of(42));
  assertNotEquals(OptionalInt.of(0), OptionalInt.empty());
}