767 lines
38 KiB
Java
767 lines
38 KiB
Java
/*
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* Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.util;
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import java.util.function.IntFunction;
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import java.util.function.Predicate;
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import java.util.stream.Stream;
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import java.util.stream.StreamSupport;
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/**
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* The root interface in the <i>collection hierarchy</i>. A collection
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* represents a group of objects, known as its <i>elements</i>. Some
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* collections allow duplicate elements and others do not. Some are ordered
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* and others unordered. The JDK does not provide any <i>direct</i>
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* implementations of this interface: it provides implementations of more
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* specific subinterfaces like {@code Set} and {@code List}. This interface
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* is typically used to pass collections around and manipulate them where
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* maximum generality is desired.
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*
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* <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain
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* duplicate elements) should implement this interface directly.
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*
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* <p>All general-purpose {@code Collection} implementation classes (which
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* typically implement {@code Collection} indirectly through one of its
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* subinterfaces) should provide two "standard" constructors: a void (no
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* arguments) constructor, which creates an empty collection, and a
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* constructor with a single argument of type {@code Collection}, which
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* creates a new collection with the same elements as its argument. In
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* effect, the latter constructor allows the user to copy any collection,
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* producing an equivalent collection of the desired implementation type.
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* There is no way to enforce this convention (as interfaces cannot contain
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* constructors) but all of the general-purpose {@code Collection}
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* implementations in the Java platform libraries comply.
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*
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* <p>Certain methods are specified to be
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* <i>optional</i>. If a collection implementation doesn't implement a
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* particular operation, it should define the corresponding method to throw
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* {@code UnsupportedOperationException}. Such methods are marked "optional
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* operation" in method specifications of the collections interfaces.
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*
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* <p><a id="optional-restrictions"></a>Some collection implementations
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* have restrictions on the elements that they may contain.
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* For example, some implementations prohibit null elements,
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* and some have restrictions on the types of their elements. Attempting to
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* add an ineligible element throws an unchecked exception, typically
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* {@code NullPointerException} or {@code ClassCastException}. Attempting
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* to query the presence of an ineligible element may throw an exception,
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* or it may simply return false; some implementations will exhibit the former
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* behavior and some will exhibit the latter. More generally, attempting an
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* operation on an ineligible element whose completion would not result in
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* the insertion of an ineligible element into the collection may throw an
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* exception or it may succeed, at the option of the implementation.
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* Such exceptions are marked as "optional" in the specification for this
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* interface.
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*
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* <p>It is up to each collection to determine its own synchronization
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* policy. In the absence of a stronger guarantee by the
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* implementation, undefined behavior may result from the invocation
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* of any method on a collection that is being mutated by another
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* thread; this includes direct invocations, passing the collection to
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* a method that might perform invocations, and using an existing
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* iterator to examine the collection.
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*
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* <p>Many methods in Collections Framework interfaces are defined in
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* terms of the {@link Object#equals(Object) equals} method. For example,
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* the specification for the {@link #contains(Object) contains(Object o)}
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* method says: "returns {@code true} if and only if this collection
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* contains at least one element {@code e} such that
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* {@code (o==null ? e==null : o.equals(e))}." This specification should
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* <i>not</i> be construed to imply that invoking {@code Collection.contains}
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* with a non-null argument {@code o} will cause {@code o.equals(e)} to be
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* invoked for any element {@code e}. Implementations are free to implement
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* optimizations whereby the {@code equals} invocation is avoided, for
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* example, by first comparing the hash codes of the two elements. (The
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* {@link Object#hashCode()} specification guarantees that two objects with
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* unequal hash codes cannot be equal.) More generally, implementations of
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* the various Collections Framework interfaces are free to take advantage of
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* the specified behavior of underlying {@link Object} methods wherever the
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* implementor deems it appropriate.
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*
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* <p>Some collection operations which perform recursive traversal of the
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* collection may fail with an exception for self-referential instances where
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* the collection directly or indirectly contains itself. This includes the
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* {@code clone()}, {@code equals()}, {@code hashCode()} and {@code toString()}
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* methods. Implementations may optionally handle the self-referential scenario,
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* however most current implementations do not do so.
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*
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* <h2><a id="view">View Collections</a></h2>
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*
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* <p>Most collections manage storage for elements they contain. By contrast, <i>view
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* collections</i> themselves do not store elements, but instead they rely on a
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* backing collection to store the actual elements. Operations that are not handled
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* by the view collection itself are delegated to the backing collection. Examples of
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* view collections include the wrapper collections returned by methods such as
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* {@link Collections#checkedCollection Collections.checkedCollection},
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* {@link Collections#synchronizedCollection Collections.synchronizedCollection}, and
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* {@link Collections#unmodifiableCollection Collections.unmodifiableCollection}.
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* Other examples of view collections include collections that provide a
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* different representation of the same elements, for example, as
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* provided by {@link List#subList List.subList},
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* {@link NavigableSet#subSet NavigableSet.subSet}, or
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* {@link Map#entrySet Map.entrySet}.
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* Any changes made to the backing collection are visible in the view collection.
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* Correspondingly, any changes made to the view collection — if changes
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* are permitted — are written through to the backing collection.
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* Although they technically aren't collections, instances of
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* {@link Iterator} and {@link ListIterator} can also allow modifications
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* to be written through to the backing collection, and in some cases,
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* modifications to the backing collection will be visible to the Iterator
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* during iteration.
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*
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* <h2><a id="unmodifiable">Unmodifiable Collections</a></h2>
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*
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* <p>Certain methods of this interface are considered "destructive" and are called
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* "mutator" methods in that they modify the group of objects contained within
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* the collection on which they operate. They can be specified to throw
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* {@code UnsupportedOperationException} if this collection implementation
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* does not support the operation. Such methods should (but are not required
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* to) throw an {@code UnsupportedOperationException} if the invocation would
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* have no effect on the collection. For example, consider a collection that
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* does not support the {@link #add add} operation. What will happen if the
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* {@link #addAll addAll} method is invoked on this collection, with an empty
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* collection as the argument? The addition of zero elements has no effect,
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* so it is permissible for this collection simply to do nothing and not to throw
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* an exception. However, it is recommended that such cases throw an exception
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* unconditionally, as throwing only in certain cases can lead to
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* programming errors.
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*
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* <p>An <i>unmodifiable collection</i> is a collection, all of whose
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* mutator methods (as defined above) are specified to throw
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* {@code UnsupportedOperationException}. Such a collection thus cannot be
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* modified by calling any methods on it. For a collection to be properly
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* unmodifiable, any view collections derived from it must also be unmodifiable.
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* For example, if a List is unmodifiable, the List returned by
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* {@link List#subList List.subList} is also unmodifiable.
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*
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* <p>An unmodifiable collection is not necessarily immutable. If the
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* contained elements are mutable, the entire collection is clearly
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* mutable, even though it might be unmodifiable. For example, consider
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* two unmodifiable lists containing mutable elements. The result of calling
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* {@code list1.equals(list2)} might differ from one call to the next if
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* the elements had been mutated, even though both lists are unmodifiable.
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* However, if an unmodifiable collection contains all immutable elements,
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* it can be considered effectively immutable.
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*
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* <h2><a id="unmodview">Unmodifiable View Collections</a></h2>
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*
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* <p>An <i>unmodifiable view collection</i> is a collection that is unmodifiable
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* and that is also a view onto a backing collection. Its mutator methods throw
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* {@code UnsupportedOperationException}, as described above, while
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* reading and querying methods are delegated to the backing collection.
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* The effect is to provide read-only access to the backing collection.
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* This is useful for a component to provide users with read access to
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* an internal collection, while preventing them from modifying such
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* collections unexpectedly. Examples of unmodifiable view collections
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* are those returned by the
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* {@link Collections#unmodifiableCollection Collections.unmodifiableCollection},
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* {@link Collections#unmodifiableList Collections.unmodifiableList}, and
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* related methods.
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*
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* <p>Note that changes to the backing collection might still be possible,
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* and if they occur, they are visible through the unmodifiable view. Thus,
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* an unmodifiable view collection is not necessarily immutable. However,
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* if the backing collection of an unmodifiable view is effectively immutable,
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* or if the only reference to the backing collection is through an
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* unmodifiable view, the view can be considered effectively immutable.
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*
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* <h2><a id="serializable">Serializability of Collections</a></h2>
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*
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* <p>Serializability of collections is optional. As such, none of the collections
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* interfaces are declared to implement the {@link java.io.Serializable} interface.
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* However, serializability is regarded as being generally useful, so most collection
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* implementations are serializable.
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*
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* <p>The collection implementations that are public classes (such as {@code ArrayList}
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* or {@code HashMap}) are declared to implement the {@code Serializable} interface if they
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* are in fact serializable. Some collections implementations are not public classes,
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* such as the <a href="#unmodifiable">unmodifiable collections.</a> In such cases, the
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* serializability of such collections is described in the specification of the method
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* that creates them, or in some other suitable place. In cases where the serializability
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* of a collection is not specified, there is no guarantee about the serializability of such
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* collections. In particular, many <a href="#view">view collections</a> are not serializable.
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*
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* <p>A collection implementation that implements the {@code Serializable} interface cannot
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* be guaranteed to be serializable. The reason is that in general, collections
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* contain elements of other types, and it is not possible to determine statically
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* whether instances of some element type are actually serializable. For example, consider
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* a serializable {@code Collection<E>}, where {@code E} does not implement the
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* {@code Serializable} interface. The collection may be serializable, if it contains only
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* elements of some serializable subtype of {@code E}, or if it is empty. Collections are
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* thus said to be <i>conditionally serializable,</i> as the serializability of the collection
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* as a whole depends on whether the collection itself is serializable and on whether all
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* contained elements are also serializable.
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*
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* <p>An additional case occurs with instances of {@link SortedSet} and {@link SortedMap}.
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* These collections can be created with a {@link Comparator} that imposes an ordering on
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* the set elements or map keys. Such a collection is serializable only if the provided
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* {@code Comparator} is also serializable.
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*
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* <p>This interface is a member of the
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* <a href="{@docRoot}/../technotes/guides/collections/index.html">
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* Java Collections Framework</a>.
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*
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* @implSpec
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* The default method implementations (inherited or otherwise) do not apply any
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* synchronization protocol. If a {@code Collection} implementation has a
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* specific synchronization protocol, then it must override default
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* implementations to apply that protocol.
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*
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* @param <E> the type of elements in this collection
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*
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* @author Josh Bloch
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* @author Neal Gafter
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* @see Set
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* @see List
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* @see Map
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* @see SortedSet
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* @see SortedMap
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* @see HashSet
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* @see TreeSet
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* @see ArrayList
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* @see LinkedList
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* @see Vector
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* @see Collections
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* @see Arrays
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* @see AbstractCollection
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* @since 1.2
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*/
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public interface Collection<E> extends Iterable<E> {
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// Query Operations
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/**
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* Returns the number of elements in this collection. If this collection
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* contains more than {@code Integer.MAX_VALUE} elements, returns
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* {@code Integer.MAX_VALUE}.
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*
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* @return the number of elements in this collection
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*/
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int size();
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/**
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* Returns {@code true} if this collection contains no elements.
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*
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* @return {@code true} if this collection contains no elements
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*/
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boolean isEmpty();
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/**
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* Returns {@code true} if this collection contains the specified element.
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* More formally, returns {@code true} if and only if this collection
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* contains at least one element {@code e} such that
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* {@code Objects.equals(o, e)}.
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*
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* @param o element whose presence in this collection is to be tested
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* @return {@code true} if this collection contains the specified
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* element
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* @throws ClassCastException if the type of the specified element
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* is incompatible with this collection
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* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
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* @throws NullPointerException if the specified element is null and this
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* collection does not permit null elements
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* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
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*/
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boolean contains(Object o);
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/**
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* Returns an iterator over the elements in this collection. There are no
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* guarantees concerning the order in which the elements are returned
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* (unless this collection is an instance of some class that provides a
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* guarantee).
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*
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* @return an {@code Iterator} over the elements in this collection
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*/
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Iterator<E> iterator();
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/**
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* Returns an array containing all of the elements in this collection.
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* If this collection makes any guarantees as to what order its elements
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* are returned by its iterator, this method must return the elements in
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* the same order. The returned array's {@linkplain Class#getComponentType
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* runtime component type} is {@code Object}.
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*
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* <p>The returned array will be "safe" in that no references to it are
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* maintained by this collection. (In other words, this method must
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* allocate a new array even if this collection is backed by an array).
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* The caller is thus free to modify the returned array.
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*
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* @apiNote
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* This method acts as a bridge between array-based and collection-based APIs.
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* It returns an array whose runtime type is {@code Object[]}.
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* Use {@link #toArray(Object[]) toArray(T[])} to reuse an existing
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* array, or use {@link #toArray(IntFunction)} to control the runtime type
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* of the array.
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*
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* @return an array, whose {@linkplain Class#getComponentType runtime component
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* type} is {@code Object}, containing all of the elements in this collection
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*/
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Object[] toArray();
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/**
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* Returns an array containing all of the elements in this collection;
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* the runtime type of the returned array is that of the specified array.
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* If the collection fits in the specified array, it is returned therein.
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* Otherwise, a new array is allocated with the runtime type of the
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* specified array and the size of this collection.
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*
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* <p>If this collection fits in the specified array with room to spare
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* (i.e., the array has more elements than this collection), the element
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* in the array immediately following the end of the collection is set to
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* {@code null}. (This is useful in determining the length of this
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* collection <i>only</i> if the caller knows that this collection does
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* not contain any {@code null} elements.)
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*
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* <p>If this collection makes any guarantees as to what order its elements
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* are returned by its iterator, this method must return the elements in
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* the same order.
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*
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* @apiNote
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* This method acts as a bridge between array-based and collection-based APIs.
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* It allows an existing array to be reused under certain circumstances.
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* Use {@link #toArray()} to create an array whose runtime type is {@code Object[]},
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* or use {@link #toArray(IntFunction)} to control the runtime type of
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* the array.
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*
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* <p>Suppose {@code x} is a collection known to contain only strings.
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* The following code can be used to dump the collection into a previously
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* allocated {@code String} array:
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*
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* <pre>
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* String[] y = new String[SIZE];
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* ...
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* y = x.toArray(y);</pre>
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*
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* <p>The return value is reassigned to the variable {@code y}, because a
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* new array will be allocated and returned if the collection {@code x} has
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* too many elements to fit into the existing array {@code y}.
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*
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* <p>Note that {@code toArray(new Object[0])} is identical in function to
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* {@code toArray()}.
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*
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* @param <T> the component type of the array to contain the collection
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* @param a the array into which the elements of this collection are to be
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* stored, if it is big enough; otherwise, a new array of the same
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* runtime type is allocated for this purpose.
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* @return an array containing all of the elements in this collection
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* @throws ArrayStoreException if the runtime type of any element in this
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* collection is not assignable to the {@linkplain Class#getComponentType
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* runtime component type} of the specified array
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* @throws NullPointerException if the specified array is null
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*/
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<T> T[] toArray(T[] a);
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/**
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* Returns an array containing all of the elements in this collection,
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* using the provided {@code generator} function to allocate the returned array.
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*
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* <p>If this collection makes any guarantees as to what order its elements
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* are returned by its iterator, this method must return the elements in
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* the same order.
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*
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* @apiNote
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* This method acts as a bridge between array-based and collection-based APIs.
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* It allows creation of an array of a particular runtime type. Use
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* {@link #toArray()} to create an array whose runtime type is {@code Object[]},
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* or use {@link #toArray(Object[]) toArray(T[])} to reuse an existing array.
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*
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* <p>Suppose {@code x} is a collection known to contain only strings.
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* The following code can be used to dump the collection into a newly
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* allocated array of {@code String}:
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*
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* <pre>
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* String[] y = x.toArray(String[]::new);</pre>
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*
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* @implSpec
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* The default implementation calls the generator function with zero
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* and then passes the resulting array to {@link #toArray(Object[]) toArray(T[])}.
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*
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* @param <T> the component type of the array to contain the collection
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* @param generator a function which produces a new array of the desired
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* type and the provided length
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* @return an array containing all of the elements in this collection
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* @throws ArrayStoreException if the runtime type of any element in this
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* collection is not assignable to the {@linkplain Class#getComponentType
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* runtime component type} of the generated array
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* @throws NullPointerException if the generator function is null
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* @since 11
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*/
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default <T> T[] toArray(IntFunction<T[]> generator) {
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return toArray(generator.apply(0));
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}
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// Modification Operations
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/**
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* Ensures that this collection contains the specified element (optional
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* operation). Returns {@code true} if this collection changed as a
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* result of the call. (Returns {@code false} if this collection does
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* not permit duplicates and already contains the specified element.)<p>
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*
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* Collections that support this operation may place limitations on what
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* elements may be added to this collection. In particular, some
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* collections will refuse to add {@code null} elements, and others will
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* impose restrictions on the type of elements that may be added.
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* Collection classes should clearly specify in their documentation any
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* restrictions on what elements may be added.<p>
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*
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* If a collection refuses to add a particular element for any reason
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* other than that it already contains the element, it <i>must</i> throw
|
|
* an exception (rather than returning {@code false}). This preserves
|
|
* the invariant that a collection always contains the specified element
|
|
* after this call returns.
|
|
*
|
|
* @param e element whose presence in this collection is to be ensured
|
|
* @return {@code true} if this collection changed as a result of the
|
|
* call
|
|
* @throws UnsupportedOperationException if the {@code add} operation
|
|
* is not supported by this collection
|
|
* @throws ClassCastException if the class of the specified element
|
|
* prevents it from being added to this collection
|
|
* @throws NullPointerException if the specified element is null and this
|
|
* collection does not permit null elements
|
|
* @throws IllegalArgumentException if some property of the element
|
|
* prevents it from being added to this collection
|
|
* @throws IllegalStateException if the element cannot be added at this
|
|
* time due to insertion restrictions
|
|
*/
|
|
boolean add(E e);
|
|
|
|
/**
|
|
* Removes a single instance of the specified element from this
|
|
* collection, if it is present (optional operation). More formally,
|
|
* removes an element {@code e} such that
|
|
* {@code Objects.equals(o, e)}, if
|
|
* this collection contains one or more such elements. Returns
|
|
* {@code true} if this collection contained the specified element (or
|
|
* equivalently, if this collection changed as a result of the call).
|
|
*
|
|
* @param o element to be removed from this collection, if present
|
|
* @return {@code true} if an element was removed as a result of this call
|
|
* @throws ClassCastException if the type of the specified element
|
|
* is incompatible with this collection
|
|
* (<a href="#optional-restrictions">optional</a>)
|
|
* @throws NullPointerException if the specified element is null and this
|
|
* collection does not permit null elements
|
|
* (<a href="#optional-restrictions">optional</a>)
|
|
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
|
|
* is not supported by this collection
|
|
*/
|
|
boolean remove(Object o);
|
|
|
|
|
|
// Bulk Operations
|
|
|
|
/**
|
|
* Returns {@code true} if this collection contains all of the elements
|
|
* in the specified collection.
|
|
*
|
|
* @param c collection to be checked for containment in this collection
|
|
* @return {@code true} if this collection contains all of the elements
|
|
* in the specified collection
|
|
* @throws ClassCastException if the types of one or more elements
|
|
* in the specified collection are incompatible with this
|
|
* collection
|
|
* (<a href="#optional-restrictions">optional</a>)
|
|
* @throws NullPointerException if the specified collection contains one
|
|
* or more null elements and this collection does not permit null
|
|
* elements
|
|
* (<a href="#optional-restrictions">optional</a>),
|
|
* or if the specified collection is null.
|
|
* @see #contains(Object)
|
|
*/
|
|
boolean containsAll(Collection<?> c);
|
|
|
|
/**
|
|
* Adds all of the elements in the specified collection to this collection
|
|
* (optional operation). The behavior of this operation is undefined if
|
|
* the specified collection is modified while the operation is in progress.
|
|
* (This implies that the behavior of this call is undefined if the
|
|
* specified collection is this collection, and this collection is
|
|
* nonempty.)
|
|
*
|
|
* @param c collection containing elements to be added to this collection
|
|
* @return {@code true} if this collection changed as a result of the call
|
|
* @throws UnsupportedOperationException if the {@code addAll} operation
|
|
* is not supported by this collection
|
|
* @throws ClassCastException if the class of an element of the specified
|
|
* collection prevents it from being added to this collection
|
|
* @throws NullPointerException if the specified collection contains a
|
|
* null element and this collection does not permit null elements,
|
|
* or if the specified collection is null
|
|
* @throws IllegalArgumentException if some property of an element of the
|
|
* specified collection prevents it from being added to this
|
|
* collection
|
|
* @throws IllegalStateException if not all the elements can be added at
|
|
* this time due to insertion restrictions
|
|
* @see #add(Object)
|
|
*/
|
|
boolean addAll(Collection<? extends E> c);
|
|
|
|
/**
|
|
* Removes all of this collection's elements that are also contained in the
|
|
* specified collection (optional operation). After this call returns,
|
|
* this collection will contain no elements in common with the specified
|
|
* collection.
|
|
*
|
|
* @param c collection containing elements to be removed from this collection
|
|
* @return {@code true} if this collection changed as a result of the
|
|
* call
|
|
* @throws UnsupportedOperationException if the {@code removeAll} method
|
|
* is not supported by this collection
|
|
* @throws ClassCastException if the types of one or more elements
|
|
* in this collection are incompatible with the specified
|
|
* collection
|
|
* (<a href="#optional-restrictions">optional</a>)
|
|
* @throws NullPointerException if this collection contains one or more
|
|
* null elements and the specified collection does not support
|
|
* null elements
|
|
* (<a href="#optional-restrictions">optional</a>),
|
|
* or if the specified collection is null
|
|
* @see #remove(Object)
|
|
* @see #contains(Object)
|
|
*/
|
|
boolean removeAll(Collection<?> c);
|
|
|
|
/**
|
|
* Removes all of the elements of this collection that satisfy the given
|
|
* predicate. Errors or runtime exceptions thrown during iteration or by
|
|
* the predicate are relayed to the caller.
|
|
*
|
|
* @implSpec
|
|
* The default implementation traverses all elements of the collection using
|
|
* its {@link #iterator}. Each matching element is removed using
|
|
* {@link Iterator#remove()}. If the collection's iterator does not
|
|
* support removal then an {@code UnsupportedOperationException} will be
|
|
* thrown on the first matching element.
|
|
*
|
|
* @param filter a predicate which returns {@code true} for elements to be
|
|
* removed
|
|
* @return {@code true} if any elements were removed
|
|
* @throws NullPointerException if the specified filter is null
|
|
* @throws UnsupportedOperationException if elements cannot be removed
|
|
* from this collection. Implementations may throw this exception if a
|
|
* matching element cannot be removed or if, in general, removal is not
|
|
* supported.
|
|
* @since 1.8
|
|
*/
|
|
default boolean removeIf(Predicate<? super E> filter) {
|
|
Objects.requireNonNull(filter);
|
|
boolean removed = false;
|
|
final Iterator<E> each = iterator();
|
|
while (each.hasNext()) {
|
|
if (filter.test(each.next())) {
|
|
each.remove();
|
|
removed = true;
|
|
}
|
|
}
|
|
return removed;
|
|
}
|
|
|
|
/**
|
|
* Retains only the elements in this collection that are contained in the
|
|
* specified collection (optional operation). In other words, removes from
|
|
* this collection all of its elements that are not contained in the
|
|
* specified collection.
|
|
*
|
|
* @param c collection containing elements to be retained in this collection
|
|
* @return {@code true} if this collection changed as a result of the call
|
|
* @throws UnsupportedOperationException if the {@code retainAll} operation
|
|
* is not supported by this collection
|
|
* @throws ClassCastException if the types of one or more elements
|
|
* in this collection are incompatible with the specified
|
|
* collection
|
|
* (<a href="#optional-restrictions">optional</a>)
|
|
* @throws NullPointerException if this collection contains one or more
|
|
* null elements and the specified collection does not permit null
|
|
* elements
|
|
* (<a href="#optional-restrictions">optional</a>),
|
|
* or if the specified collection is null
|
|
* @see #remove(Object)
|
|
* @see #contains(Object)
|
|
*/
|
|
boolean retainAll(Collection<?> c);
|
|
|
|
/**
|
|
* Removes all of the elements from this collection (optional operation).
|
|
* The collection will be empty after this method returns.
|
|
*
|
|
* @throws UnsupportedOperationException if the {@code clear} operation
|
|
* is not supported by this collection
|
|
*/
|
|
void clear();
|
|
|
|
|
|
// Comparison and hashing
|
|
|
|
/**
|
|
* Compares the specified object with this collection for equality. <p>
|
|
*
|
|
* While the {@code Collection} interface adds no stipulations to the
|
|
* general contract for the {@code Object.equals}, programmers who
|
|
* implement the {@code Collection} interface "directly" (in other words,
|
|
* create a class that is a {@code Collection} but is not a {@code Set}
|
|
* or a {@code List}) must exercise care if they choose to override the
|
|
* {@code Object.equals}. It is not necessary to do so, and the simplest
|
|
* course of action is to rely on {@code Object}'s implementation, but
|
|
* the implementor may wish to implement a "value comparison" in place of
|
|
* the default "reference comparison." (The {@code List} and
|
|
* {@code Set} interfaces mandate such value comparisons.)<p>
|
|
*
|
|
* The general contract for the {@code Object.equals} method states that
|
|
* equals must be symmetric (in other words, {@code a.equals(b)} if and
|
|
* only if {@code b.equals(a)}). The contracts for {@code List.equals}
|
|
* and {@code Set.equals} state that lists are only equal to other lists,
|
|
* and sets to other sets. Thus, a custom {@code equals} method for a
|
|
* collection class that implements neither the {@code List} nor
|
|
* {@code Set} interface must return {@code false} when this collection
|
|
* is compared to any list or set. (By the same logic, it is not possible
|
|
* to write a class that correctly implements both the {@code Set} and
|
|
* {@code List} interfaces.)
|
|
*
|
|
* @param o object to be compared for equality with this collection
|
|
* @return {@code true} if the specified object is equal to this
|
|
* collection
|
|
*
|
|
* @see Object#equals(Object)
|
|
* @see Set#equals(Object)
|
|
* @see List#equals(Object)
|
|
*/
|
|
boolean equals(Object o);
|
|
|
|
/**
|
|
* Returns the hash code value for this collection. While the
|
|
* {@code Collection} interface adds no stipulations to the general
|
|
* contract for the {@code Object.hashCode} method, programmers should
|
|
* take note that any class that overrides the {@code Object.equals}
|
|
* method must also override the {@code Object.hashCode} method in order
|
|
* to satisfy the general contract for the {@code Object.hashCode} method.
|
|
* In particular, {@code c1.equals(c2)} implies that
|
|
* {@code c1.hashCode()==c2.hashCode()}.
|
|
*
|
|
* @return the hash code value for this collection
|
|
*
|
|
* @see Object#hashCode()
|
|
* @see Object#equals(Object)
|
|
*/
|
|
int hashCode();
|
|
|
|
/**
|
|
* Creates a {@link Spliterator} over the elements in this collection.
|
|
*
|
|
* Implementations should document characteristic values reported by the
|
|
* spliterator. Such characteristic values are not required to be reported
|
|
* if the spliterator reports {@link Spliterator#SIZED} and this collection
|
|
* contains no elements.
|
|
*
|
|
* <p>The default implementation should be overridden by subclasses that
|
|
* can return a more efficient spliterator. In order to
|
|
* preserve expected laziness behavior for the {@link #stream()} and
|
|
* {@link #parallelStream()} methods, spliterators should either have the
|
|
* characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be
|
|
* <em><a href="Spliterator.html#binding">late-binding</a></em>.
|
|
* If none of these is practical, the overriding class should describe the
|
|
* spliterator's documented policy of binding and structural interference,
|
|
* and should override the {@link #stream()} and {@link #parallelStream()}
|
|
* methods to create streams using a {@code Supplier} of the spliterator,
|
|
* as in:
|
|
* <pre>{@code
|
|
* Stream<E> s = StreamSupport.stream(() -> spliterator(), spliteratorCharacteristics)
|
|
* }</pre>
|
|
* <p>These requirements ensure that streams produced by the
|
|
* {@link #stream()} and {@link #parallelStream()} methods will reflect the
|
|
* contents of the collection as of initiation of the terminal stream
|
|
* operation.
|
|
*
|
|
* @implSpec
|
|
* The default implementation creates a
|
|
* <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
|
|
* from the collection's {@code Iterator}. The spliterator inherits the
|
|
* <em>fail-fast</em> properties of the collection's iterator.
|
|
* <p>
|
|
* The created {@code Spliterator} reports {@link Spliterator#SIZED}.
|
|
*
|
|
* @implNote
|
|
* The created {@code Spliterator} additionally reports
|
|
* {@link Spliterator#SUBSIZED}.
|
|
*
|
|
* <p>If a spliterator covers no elements then the reporting of additional
|
|
* characteristic values, beyond that of {@code SIZED} and {@code SUBSIZED},
|
|
* does not aid clients to control, specialize or simplify computation.
|
|
* However, this does enable shared use of an immutable and empty
|
|
* spliterator instance (see {@link Spliterators#emptySpliterator()}) for
|
|
* empty collections, and enables clients to determine if such a spliterator
|
|
* covers no elements.
|
|
*
|
|
* @return a {@code Spliterator} over the elements in this collection
|
|
* @since 1.8
|
|
*/
|
|
@Override
|
|
default Spliterator<E> spliterator() {
|
|
return Spliterators.spliterator(this, 0);
|
|
}
|
|
|
|
/**
|
|
* Returns a sequential {@code Stream} with this collection as its source.
|
|
*
|
|
* <p>This method should be overridden when the {@link #spliterator()}
|
|
* method cannot return a spliterator that is {@code IMMUTABLE},
|
|
* {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
|
|
* for details.)
|
|
*
|
|
* @implSpec
|
|
* The default implementation creates a sequential {@code Stream} from the
|
|
* collection's {@code Spliterator}.
|
|
*
|
|
* @return a sequential {@code Stream} over the elements in this collection
|
|
* @since 1.8
|
|
*/
|
|
default Stream<E> stream() {
|
|
return StreamSupport.stream(spliterator(), false);
|
|
}
|
|
|
|
/**
|
|
* Returns a possibly parallel {@code Stream} with this collection as its
|
|
* source. It is allowable for this method to return a sequential stream.
|
|
*
|
|
* <p>This method should be overridden when the {@link #spliterator()}
|
|
* method cannot return a spliterator that is {@code IMMUTABLE},
|
|
* {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
|
|
* for details.)
|
|
*
|
|
* @implSpec
|
|
* The default implementation creates a parallel {@code Stream} from the
|
|
* collection's {@code Spliterator}.
|
|
*
|
|
* @return a possibly parallel {@code Stream} over the elements in this
|
|
* collection
|
|
* @since 1.8
|
|
*/
|
|
default Stream<E> parallelStream() {
|
|
return StreamSupport.stream(spliterator(), true);
|
|
}
|
|
}
|