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Infinispan core module
There is a newer version: 15.1.0.Dev04
package org.infinispan.util;

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.stream.Stream;

import org.infinispan.commons.util.IteratorMapper;
import org.infinispan.commons.util.SpliteratorMapper;

/**
 * A collection that maps another one to a new one of a possibly different type.  Note this collection is read only
 * and doesn't accept write operations.
 * 
 * Some operations such as {@link Collection#contains(Object)} and {@link Collection#containsAll(Collection)} may be
 * more expensive then normal since they cannot utilize lookups into the original collection.
 * @author wburns
 * @since 9.0
 */
public class CollectionMapper extends AbstractCollection {
   protected final Collection realCollection;
   protected final Function mapper;

   public CollectionMapper(Collection realCollection, Function mapper) {
      this.realCollection = realCollection;
      this.mapper = mapper;
   }

   @Override
   public int size() {
      return realCollection.size();
   }

   @Override
   public boolean isEmpty() {
      return realCollection.isEmpty();
   }

   @Override
   public Iterator iterator() {
      return new IteratorMapper(realCollection.iterator(), mapper) {
         @Override
         public void remove() {
            throw new UnsupportedOperationException("remove");
         }
      };
   }

   @Override
   public Spliterator spliterator() {
      return new SpliteratorMapper<>(realCollection.spliterator(), mapper);
   }

   @Override
   public Stream stream() {
      return realCollection.stream().map(mapper);
   }

   @Override
   public Stream parallelStream() {
      return realCollection.parallelStream().map(mapper);
   }

   @Override
   public void forEach(Consumer action) {
      realCollection.forEach(c -> action.accept(mapper.apply(c)));
   }

   // Write operations are not supported!
   @Override
   public boolean add(R e) {
      throw new UnsupportedOperationException();
   }

   @Override
   public boolean remove(Object o) {
      throw new UnsupportedOperationException();
   }

   @Override
   public boolean addAll(Collection c) {
      throw new UnsupportedOperationException();
   }

   @Override
   public boolean removeAll(Collection c) {
      throw new UnsupportedOperationException();
   }

   @Override
   public boolean retainAll(Collection c) {
      throw new UnsupportedOperationException();
   }

   @Override
   public void clear() {
      throw new UnsupportedOperationException();
   }
}