FilteredIterable.java from DrJava at Krugle

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/*BEGIN_COPYRIGHT_BLOCK*

PLT Utilities BSD License

Copyright (c) 2007 JavaPLT group at Rice University
All rights reserved.

Developed by:   Java Programming Languages Team
                Rice University
                http://www.cs.rice.edu/~javaplt/

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    - Redistributions of source code must retain the above copyright notice, this list of conditions 
      and the following disclaimer.
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      conditions and the following disclaimer in the documentation and/or other materials provided 
      with the distribution.
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      contributors may be used to endorse or promote products derived from this software without 
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package edu.rice.cs.plt.iter;

import java.io.Serializable;
import edu.rice.cs.plt.lambda.Predicate;

/**
 * An Iterable containing all the values in the provided Iterable for which the provided
 * Predicate holds.  Because the size cannot be determined without traversing the list,
 * does not implement {@code SizedIterable}.
 */
public class FilteredIterable<T> extends AbstractIterable<T> implements Iterable<T>, Serializable {
  
  private Iterable<? extends T> _iterable;
  private Predicate<? super T> _predicate;
  
  public FilteredIterable(Iterable<? extends T> iterable, Predicate<? super T> predicate) {
    _iterable = iterable;
    _predicate = predicate;
  }
  
  public FilteredIterator<T> iterator() { 
    return new FilteredIterator<T>(_iterable.iterator(), _predicate);
  }
  
  /**
   * Determine whether this iterable is infinite.  While the exact size is expensive to determine, testing
   * for infiniteness is not.  So despite not implementing {@code SizedIterable}, this class provides this method.
   */
  public boolean isInfinite() { return IterUtil.isInfinite(_iterable); }
  
  /** Call the constructor (allows {@code T} to be inferred) */
  public static <T> FilteredIterable<T> make(Iterable<? extends T> iterable, 
                                             Predicate<? super T> predicate) {
    return new FilteredIterable<T>(iterable, predicate);
  }
  
  /**
   * Create a {@code FilteredIterable} and wrap it in a {@code SnapshotIterable}, forcing
   * immediate evaluation of the filter.
   */
  public static <T> SnapshotIterable<T> makeSnapshot(Iterable<? extends T> iterable,
                                                     Predicate<? super T> predicate) {
    return new SnapshotIterable<T>(new FilteredIterable<T>(iterable, predicate));
  }
}
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