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This is just a guess, but part of the reason why an unmodifiable implementation was not provided may be due to the fact that the NavigableSet/Map interfaces expose mutating methods that aren't marked as optional: <ul> <li>NavigableSet.pollFirst</li> <li>NavigableSet.pollLast</li> <li>NavigableMap.pollFirstEntry </li> <li>NavigableMap.pollLastEntry</li> </ul> That said, it seems reasonable when providing an unmodifiable implementation to just throw an UnsupportedOperationException. That is what is done in these implementations (which assume you're using GoogleGuava): NavigableSet: <pre><code>import static java.util.Collections.unmodifiableSortedSet; import java.util.Collections; import java.util.Iterator; import java.util.NavigableSet; import java.util.SortedSet; import com.google.common.collect.ForwardingSortedSet; /** * {@link NavigableSet} equivalent of {@link Collections#unmodifiableSortedSet(SortedSet)}. * This is unfortunately needed because {@link Collections} lacks "UnmodifiableNavigableSet" * (see http://stackoverflow.com/questions/2577706/unmodifiable-navigableset-navigablemap-in-java * and http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6907251). * * This is just a guess, but part of the reason why an unmodifiable implementation was not provided may be due to the fact that * {@link NavigableSet} exposes mutating methods that aren't marked as optional: * - {@link NavigableSet#pollFirst()} * - {@link NavigableSet#pollLast()} * * In addition, one can't go the immutable route, as Google Guava doesn't provide an Immutable variant * (see http://code.google.com/p/guava-libraries/issues/detail?id=664). * * @param <E> See {@link NavigableSet} */ public final class UnmodifiableNavigableSet<E> extends ForwardingSortedSet<E> implements NavigableSet<E> { private final NavigableSet<E> delegate; private final SortedSet<E> unmodifiableDelegate; /** * @param delegate See {@link ForwardingSortedSet#delegate()}. */ public UnmodifiableNavigableSet(NavigableSet<E> delegate) { this.delegate = delegate; unmodifiableDelegate = unmodifiableSortedSet(delegate); } /** * @param delegate * @return {@link #UnmodifiableNavigableSet(NavigableSet)} * @see EffectiveJava#Static_factories_instead_of_constructors */ public static <E> UnmodifiableNavigableSet<E> newUnmodifiableNavigableSet(NavigableSet<E> delegate) { return new UnmodifiableNavigableSet<E>(delegate); } @Override protected SortedSet<E> delegate() { return unmodifiableDelegate; } @Override public E ceiling(E e) { return delegate.ceiling(e); } @Override public Iterator<E> descendingIterator() { // NavigableSet.descendingIterator explicitly states this behavior. // By doing this, we don't need to do anything extra to ensure the iterator is unmodifiable. return descendingSet().iterator(); } @Override public NavigableSet<E> descendingSet() { return newUnmodifiableNavigableSet(delegate.descendingSet()); } @Override public E floor(E e) { return delegate.floor(e); } @Override public NavigableSet<E> headSet(E toElement, boolean inclusive) { return newUnmodifiableNavigableSet(delegate.headSet(toElement, inclusive)); } @Override public E higher(E e) { return delegate.higher(e); } @Override public E lower(E e) { return delegate.lower(e); } @Override public E pollFirst() { throw new UnsupportedOperationException(); } @Override public E pollLast() { throw new UnsupportedOperationException(); } @Override public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { return newUnmodifiableNavigableSet(delegate.subSet(fromElement, fromInclusive, toElement, toInclusive)); } @Override public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { return newUnmodifiableNavigableSet(delegate.tailSet(fromElement, inclusive)); } } </code></pre> NavigableMap: <pre><code>import static UnmodifiableNavigableSet.newUnmodifiableNavigableSet; import static java.util.Collections.unmodifiableSortedMap; import java.util.AbstractMap; import java.util.Map; import java.util.NavigableMap; import java.util.NavigableSet; import java.util.SortedMap; import com.google.common.collect.ForwardingSortedMap; /** * This class has the same rational as {@link UnmodifiableNavigableSet}. * @param <K> See {@link NavigableMap} * @param <V> See {@link NavigableMap} */ public final class UnmodifiableNavigableMap<K,V> extends ForwardingSortedMap<K,V> implements NavigableMap<K,V> { private final NavigableMap<K,V> delegate; private final SortedMap<K,V> unmodifiableDelegate; /** * @param delegate See {@link ForwardingSortedMap#delegate()}. */ public UnmodifiableNavigableMap(NavigableMap<K,V> delegate) { this.delegate = delegate; unmodifiableDelegate = unmodifiableSortedMap(delegate); } /** * @param delegate * @return {@link #UnmodifiableNavigableMap(NavigableMap)} * @see EffectiveJava#Static_factories_instead_of_constructors */ public static <K,V> UnmodifiableNavigableMap<K,V> newUnmodifiableNavigableMap(NavigableMap<K,V> delegate) { return new UnmodifiableNavigableMap<K,V>(delegate); } @Override protected SortedMap<K,V> delegate() { return unmodifiableDelegate; } private Map.Entry<K,V> newImmutableEntry(Map.Entry<K,V> entry) { return entry == null ? null : new AbstractMap.SimpleImmutableEntry<K,V>(entry); } @Override public Map.Entry<K,V> ceilingEntry(K key) { return newImmutableEntry(delegate.ceilingEntry(key)); } @Override public K ceilingKey(K key) { return delegate.ceilingKey(key); } @Override public NavigableSet<K> descendingKeySet() { return newUnmodifiableNavigableSet(delegate.descendingKeySet()); } @Override public NavigableMap<K,V> descendingMap() { return newUnmodifiableNavigableMap(delegate.descendingMap()); } @Override public Map.Entry<K,V> firstEntry() { return newImmutableEntry(delegate.firstEntry()); } @Override public Map.Entry<K,V> floorEntry(K key) { return newImmutableEntry(delegate.floorEntry(key)); } @Override public K floorKey(K key) { return delegate.floorKey(key); } @Override public NavigableMap<K,V> headMap(K toKey, boolean inclusive) { return newUnmodifiableNavigableMap(delegate.headMap(toKey, inclusive)); } @Override public Map.Entry<K,V> higherEntry(K key) { return newImmutableEntry(delegate.higherEntry(key)); } @Override public K higherKey(K key) { return delegate.higherKey(key); } @Override public Map.Entry<K,V> lastEntry() { return newImmutableEntry(delegate.lastEntry()); } @Override public Map.Entry<K,V> lowerEntry(K key) { return newImmutableEntry(delegate.lowerEntry(key)); } @Override public K lowerKey(K key) { return delegate.lowerKey(key); } @Override public NavigableSet<K> navigableKeySet() { return newUnmodifiableNavigableSet(delegate.navigableKeySet()); } @Override public Map.Entry<K,V> pollFirstEntry() { throw new UnsupportedOperationException(); } @Override public Map.Entry<K,V> pollLastEntry() { throw new UnsupportedOperationException(); } @Override public NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { return newUnmodifiableNavigableMap(delegate.subMap(fromKey, fromInclusive, toKey, toInclusive)); } @Override public NavigableMap<K,V> tailMap(K fromKey, boolean inclusive) { return newUnmodifiableNavigableMap(delegate.tailMap(fromKey, inclusive)); } } </code></pre>
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1. POUnmodifiable NavigableSet/NavigableMap in Java?
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1. COWell done! I'm not familiar with "com.amazon.agua.collections." I realize that you're just referencing the Set code in the Map code, but is there some publicly available package where this stuff will be maintained? It would make a nice addition to the JDK.
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