All Downloads are FREE. Search and download functionalities are using the official Maven repository.
  • Log In
  • Register

    • com.google.common.collect.MoreCollectors Maven / Gradle / Ivy

    Go to download

    This artifact provides a single jar that contains all classes required to use remote Jakarta Enterprise Beans and Jakarta Messaging, including all dependencies. It is intended for use by those not using maven, maven users should just import the Jakarta Enterprise Beans and Jakarta Messaging BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up with different versions on classes on the class path).

    There is a newer version: 35.0.0.Beta1
    Show newest version
    /*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import java.util.ArrayList;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.stream.Collector;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;

/**
 * Collectors not present in {@code java.util.stream.Collectors} that are not otherwise associated
 * with a {@code com.google.common} type.
 *
 * @author Louis Wasserman
 * @since 21.0
 */
@Beta
@GwtCompatible
public final class MoreCollectors {

  /*
   * TODO(lowasser): figure out if we can convert this to a concurrent AtomicReference-based
   * collector without breaking j2cl?
   */
  private static final Collector> TO_OPTIONAL =
      Collector.of(
          ToOptionalState::new,
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}. The returned
   * collector throws an {@code IllegalArgumentException} if the stream consists of two or more
   * elements, and a {@code NullPointerException} if the stream consists of exactly one element,
   * which is null.
   */
  @SuppressWarnings("unchecked")
  public static  Collector> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

  private static final Collector ONLY_ELEMENT =
      Collector.of(
          ToOptionalState::new,
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,
          state -> {
            Object result = state.getElement();
            return (result == NULL_PLACEHOLDER) ? null : result;
          },
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that takes a stream containing exactly one element and returns that element. The
   * returned collector throws an {@code IllegalArgumentException} if the stream consists of two or
   * more elements, and a {@code NoSuchElementException} if the stream is empty.
   */
  @SuppressWarnings("unchecked")
  public static  Collector onlyElement() {
    return (Collector) ONLY_ELEMENT;
  }

  /**
   * This atrocity is here to let us report several of the elements in the stream if there were more
   * than one, not just two.
   */
  private static final class ToOptionalState {
    static final int MAX_EXTRAS = 4;

    @NullableDecl Object element;
    @NullableDecl List extras;

    ToOptionalState() {
      element = null;
      extras = null;
    }

    IllegalArgumentException multiples(boolean overflow) {
      StringBuilder sb =
          new StringBuilder().append("expected one element but was: <").append(element);
      for (Object o : extras) {
        sb.append(", ").append(o);
      }
      if (overflow) {
        sb.append(", ...");
      }
      sb.append('>');
      throw new IllegalArgumentException(sb.toString());
    }

    void add(Object o) {
      checkNotNull(o);
      if (element == null) {
        this.element = o;
      } else if (extras == null) {
        extras = new ArrayList<>(MAX_EXTRAS);
        extras.add(o);
      } else if (extras.size() < MAX_EXTRAS) {
        extras.add(o);
      } else {
        throw multiples(true);
      }
    }

    ToOptionalState combine(ToOptionalState other) {
      if (element == null) {
        return other;
      } else if (other.element == null) {
        return this;
      } else {
        if (extras == null) {
          extras = new ArrayList<>();
        }
        extras.add(other.element);
        if (other.extras != null) {
          this.extras.addAll(other.extras);
        }
        if (extras.size() > MAX_EXTRAS) {
          extras.subList(MAX_EXTRAS, extras.size()).clear();
          throw multiples(true);
        }
        return this;
      }
    }

    Optional getOptional() {
      if (extras == null) {
        return Optional.ofNullable(element);
      } else {
        throw multiples(false);
      }
    }

    Object getElement() {
      if (element == null) {
        throw new NoSuchElementException();
      } else if (extras == null) {
        return element;
      } else {
        throw multiples(false);
      }
    }
  }

  private MoreCollectors() {}
}
    
    
    
    

    




    
    
    © 2015 - 2025 Weber Informatics LLC | Privacy Policy