content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 org.apache.kafka.server.immutable;
  
  import org.apache.kafka.server.immutable.pcollections.PCollectionsImmutableSet;
  
  import java.util.Set;
  
  /**
   * A persistent Hash-based Set wrapper
   * java.util.Set methods that mutate in-place will throw UnsupportedOperationException
   *
   * @param <E> the element type
   */
  public interface ImmutableSet<E> extends Set<E> {
  
      /**
       * @return a wrapped hash-based persistent set that is empty
       * @param <E> the element type
       */
      static <E> ImmutableSet<E> empty() {
          return PCollectionsImmutableSet.empty();
      }
  
      /**
       * @param e the element
       * @return a wrapped hash-based persistent set that has a single element
       * @param <E> the element type
       */
      static <E> ImmutableSet<E> singleton(E e) {
          return PCollectionsImmutableSet.singleton(e);
      }
  
      /**
       * @param e the element
       * @return a wrapped persistent set that differs from this one in that the given element is added (if necessary)
       */
      ImmutableSet<E> added(E e);
  
      /**
       * @param e the element
       * @return a wrapped persistent set that differs from this one in that the given element is added (if necessary)
       */
      ImmutableSet<E> removed(E e);
  }
  