- java.lang.Object
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- java.util.AbstractCollection<E>
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- java.util.AbstractList<E>
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- java.util.ArrayList<E>
 
 
 
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- Type Parameters:
- E- the type of elements in this list
 - All Implemented Interfaces:
- Serializable,- Cloneable,- Iterable<E>,- Collection<E>,- List<E>,- RandomAccess
 - Direct Known Subclasses:
- AttributeList,- RoleList,- RoleUnresolvedList
 
 public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, Serializable Resizable-array implementation of theListinterface. Implements all optional list operations, and permits all elements, includingnull. In addition to implementing theListinterface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent toVector, except that it is unsynchronized.)The size,isEmpty,get,set,iterator, andlistIteratoroperations run in constant time. Theaddoperation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for theLinkedListimplementation.Each ArrayListinstance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.An application can increase the capacity of an ArrayListinstance before adding a large number of elements using theensureCapacityoperation. This may reduce the amount of incremental reallocation.Note that this implementation is not synchronized. If multiple threads access an ArrayListinstance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be "wrapped" using theCollections.synchronizedListmethod. This is best done at creation time, to prevent accidental unsynchronized access to the list:List list = Collections.synchronizedList(new ArrayList(...)); The iterators returned by this class's iteratorandlistIteratormethods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's ownremoveoraddmethods, the iterator will throw aConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationExceptionon a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.This class is a member of the Java Collections Framework. - Since:
- 1.2
- See Also:
- Collection,- List,- LinkedList,- Vector, Serialized Form
 
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Field Summary- 
Fields declared in class java.util.AbstractListmodCount
 
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Constructor SummaryConstructors Constructor Description ArrayList()Constructs an empty list with an initial capacity of ten.ArrayList(int initialCapacity)Constructs an empty list with the specified initial capacity.ArrayList(Collection<? extends E> c)Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
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Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description voidadd(int index, E element)Inserts the specified element at the specified position in this list.booleanadd(E e)Appends the specified element to the end of this list.booleanaddAll(int index, Collection<? extends E> c)Inserts all of the elements in the specified collection into this list, starting at the specified position.booleanaddAll(Collection<? extends E> c)Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator.voidclear()Removes all of the elements from this list.Objectclone()Returns a shallow copy of thisArrayListinstance.booleancontains(Object o)Returnstrueif this list contains the specified element.voidensureCapacity(int minCapacity)Increases the capacity of thisArrayListinstance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.voidforEach(Consumer<? super E> action)Performs the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.Eget(int index)Returns the element at the specified position in this list.intindexOf(Object o)Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.booleanisEmpty()Returnstrueif this list contains no elements.Iterator<E>iterator()Returns an iterator over the elements in this list in proper sequence.intlastIndexOf(Object o)Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.ListIterator<E>listIterator()Returns a list iterator over the elements in this list (in proper sequence).ListIterator<E>listIterator(int index)Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.Eremove(int index)Removes the element at the specified position in this list.booleanremove(Object o)Removes the first occurrence of the specified element from this list, if it is present.booleanremoveAll(Collection<?> c)Removes from this list all of its elements that are contained in the specified collection.booleanremoveIf(Predicate<? super E> filter)Removes all of the elements of this collection that satisfy the given predicate.protected voidremoveRange(int fromIndex, int toIndex)Removes from this list all of the elements whose index is betweenfromIndex, inclusive, andtoIndex, exclusive.booleanretainAll(Collection<?> c)Retains only the elements in this list that are contained in the specified collection.Eset(int index, E element)Replaces the element at the specified position in this list with the specified element.intsize()Returns the number of elements in this list.Spliterator<E>spliterator()Creates a late-binding and fail-fastSpliteratorover the elements in this list.List<E>subList(int fromIndex, int toIndex)Returns a view of the portion of this list between the specifiedfromIndex, inclusive, andtoIndex, exclusive.Object[]toArray()Returns an array containing all of the elements in this list in proper sequence (from first to last element).<T> T[]toArray(T[] a)Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.voidtrimToSize()Trims the capacity of thisArrayListinstance to be the list's current size.- 
Methods declared in class java.util.AbstractListequals, hashCode
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Methods declared in class java.util.AbstractCollectioncontainsAll, toString
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Methods declared in interface java.util.CollectionparallelStream, stream, toArray
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Methods declared in interface java.util.ListcontainsAll, equals, hashCode, replaceAll, sort
 
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Constructor Detail- 
ArrayListpublic ArrayList(int initialCapacity) Constructs an empty list with the specified initial capacity.- Parameters:
- initialCapacity- the initial capacity of the list
- Throws:
- IllegalArgumentException- if the specified initial capacity is negative
 
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ArrayListpublic ArrayList() Constructs an empty list with an initial capacity of ten.
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ArrayListpublic ArrayList(Collection<? extends E> c) Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.- Parameters:
- c- the collection whose elements are to be placed into this list
- Throws:
- NullPointerException- if the specified collection is null
 
 
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Method Detail- 
trimToSizepublic void trimToSize() Trims the capacity of thisArrayListinstance to be the list's current size. An application can use this operation to minimize the storage of anArrayListinstance.
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ensureCapacitypublic void ensureCapacity(int minCapacity) Increases the capacity of thisArrayListinstance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.- Parameters:
- minCapacity- the desired minimum capacity
 
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sizepublic int size() Returns the number of elements in this list.
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isEmptypublic boolean isEmpty() Returnstrueif this list contains no elements.- Specified by:
- isEmptyin interface- Collection<E>
- Specified by:
- isEmptyin interface- List<E>
- Overrides:
- isEmptyin class- AbstractCollection<E>
- Returns:
- trueif this list contains no elements
 
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containspublic boolean contains(Object o) Returnstrueif this list contains the specified element. More formally, returnstrueif and only if this list contains at least one elementesuch thatObjects.equals(o, e).- Specified by:
- containsin interface- Collection<E>
- Specified by:
- containsin interface- List<E>
- Overrides:
- containsin class- AbstractCollection<E>
- Parameters:
- o- element whose presence in this list is to be tested
- Returns:
- trueif this list contains the specified element
 
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indexOfpublic int indexOf(Object o) Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index.
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lastIndexOfpublic int lastIndexOf(Object o) Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the highest indexisuch thatObjects.equals(o, get(i)), or -1 if there is no such index.- Specified by:
- lastIndexOfin interface- List<E>
- Overrides:
- lastIndexOfin class- AbstractList<E>
- Parameters:
- o- element to search for
- Returns:
- the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
 
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clonepublic Object clone() Returns a shallow copy of thisArrayListinstance. (The elements themselves are not copied.)
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toArraypublic Object[] toArray() Returns an array containing all of the elements in this list in proper sequence (from first to last element).The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array. This method acts as bridge between array-based and collection-based APIs. - Specified by:
- toArrayin interface- Collection<E>
- Specified by:
- toArrayin interface- List<E>
- Overrides:
- toArrayin class- AbstractCollection<E>
- Returns:
- an array containing all of the elements in this list in proper sequence
- See Also:
- Arrays.asList(Object[])
 
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toArraypublic <T> T[] toArray(T[] a) Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list.If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.)- Specified by:
- toArrayin interface- Collection<E>
- Specified by:
- toArrayin interface- List<E>
- Overrides:
- toArrayin class- AbstractCollection<E>
- Type Parameters:
- T- the component type of the array to contain the collection
- Parameters:
- a- the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
- Returns:
- an array containing the elements of the list
- Throws:
- ArrayStoreException- if the runtime type of the specified array is not a supertype of the runtime type of every element in this list
- NullPointerException- if the specified array is null
 
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getpublic E get(int index) Returns the element at the specified position in this list.- Specified by:
- getin interface- List<E>
- Specified by:
- getin class- AbstractList<E>
- Parameters:
- index- index of the element to return
- Returns:
- the element at the specified position in this list
- Throws:
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index >= size())
 
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setpublic E set(int index, E element) Replaces the element at the specified position in this list with the specified element.- Specified by:
- setin interface- List<E>
- Overrides:
- setin class- AbstractList<E>
- Parameters:
- index- index of the element to replace
- element- element to be stored at the specified position
- Returns:
- the element previously at the specified position
- Throws:
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index >= size())
 
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addpublic boolean add(E e) Appends the specified element to the end of this list.- Specified by:
- addin interface- Collection<E>
- Specified by:
- addin interface- List<E>
- Overrides:
- addin class- AbstractList<E>
- Parameters:
- e- element to be appended to this list
- Returns:
- true(as specified by- Collection.add(E))
 
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addpublic void add(int index, E element)Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).- Specified by:
- addin interface- List<E>
- Overrides:
- addin class- AbstractList<E>
- Parameters:
- index- index at which the specified element is to be inserted
- element- element to be inserted
- Throws:
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index > size())
 
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removepublic E remove(int index) Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).- Specified by:
- removein interface- List<E>
- Overrides:
- removein class- AbstractList<E>
- Parameters:
- index- the index of the element to be removed
- Returns:
- the element that was removed from the list
- Throws:
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index >= size())
 
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removepublic boolean remove(Object o) Removes the first occurrence of the specified element from this list, if it is present. If the list does not contain the element, it is unchanged. More formally, removes the element with the lowest indexisuch thatObjects.equals(o, get(i))(if such an element exists). Returnstrueif this list contained the specified element (or equivalently, if this list changed as a result of the call).- Specified by:
- removein interface- Collection<E>
- Specified by:
- removein interface- List<E>
- Overrides:
- removein class- AbstractCollection<E>
- Parameters:
- o- element to be removed from this list, if present
- Returns:
- trueif this list contained the specified element
 
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clearpublic void clear() Removes all of the elements from this list. The list will be empty after this call returns.- Specified by:
- clearin interface- Collection<E>
- Specified by:
- clearin interface- List<E>
- Overrides:
- clearin class- AbstractList<E>
 
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addAllpublic boolean addAll(Collection<? extends E> c) Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator. 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 list, and this list is nonempty.)- Specified by:
- addAllin interface- Collection<E>
- Specified by:
- addAllin interface- List<E>
- Overrides:
- addAllin class- AbstractCollection<E>
- Parameters:
- c- collection containing elements to be added to this list
- Returns:
- trueif this list changed as a result of the call
- Throws:
- NullPointerException- if the specified collection is null
- See Also:
- AbstractCollection.add(Object)
 
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addAllpublic boolean addAll(int index, Collection<? extends E> c)Inserts all of the elements in the specified collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in the list in the order that they are returned by the specified collection's iterator.- Specified by:
- addAllin interface- List<E>
- Overrides:
- addAllin class- AbstractList<E>
- Parameters:
- index- index at which to insert the first element from the specified collection
- c- collection containing elements to be added to this list
- Returns:
- trueif this list changed as a result of the call
- Throws:
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index > size())
- NullPointerException- if the specified collection is null
 
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removeRangeprotected void removeRange(int fromIndex, int toIndex)Removes from this list all of the elements whose index is betweenfromIndex, inclusive, andtoIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by(toIndex - fromIndex)elements. (IftoIndex==fromIndex, this operation has no effect.)- Overrides:
- removeRangein class- AbstractList<E>
- Parameters:
- fromIndex- index of first element to be removed
- toIndex- index after last element to be removed
- Throws:
- IndexOutOfBoundsException- if- fromIndexor- toIndexis out of range (- fromIndex < 0 || toIndex > size() || toIndex < fromIndex)
 
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removeAllpublic boolean removeAll(Collection<?> c) Removes from this list all of its elements that are contained in the specified collection.- Specified by:
- removeAllin interface- Collection<E>
- Specified by:
- removeAllin interface- List<E>
- Overrides:
- removeAllin class- AbstractCollection<E>
- Parameters:
- c- collection containing elements to be removed from this list
- Returns:
- trueif this list changed as a result of the call
- Throws:
- ClassCastException- if the class of an element of this list is incompatible with the specified collection (optional)
- NullPointerException- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null
- See Also:
- Collection.contains(Object)
 
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retainAllpublic boolean retainAll(Collection<?> c) Retains only the elements in this list that are contained in the specified collection. In other words, removes from this list all of its elements that are not contained in the specified collection.- Specified by:
- retainAllin interface- Collection<E>
- Specified by:
- retainAllin interface- List<E>
- Overrides:
- retainAllin class- AbstractCollection<E>
- Parameters:
- c- collection containing elements to be retained in this list
- Returns:
- trueif this list changed as a result of the call
- Throws:
- ClassCastException- if the class of an element of this list is incompatible with the specified collection (optional)
- NullPointerException- if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null
- See Also:
- Collection.contains(Object)
 
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listIteratorpublic ListIterator<E> listIterator(int index) Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call tonext. An initial call topreviouswould return the element with the specified index minus one.The returned list iterator is fail-fast. - Specified by:
- listIteratorin interface- List<E>
- Overrides:
- listIteratorin class- AbstractList<E>
- Parameters:
- index- index of the first element to be returned from the list iterator (by a call to- next)
- Returns:
- a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list
- Throws:
- IndexOutOfBoundsException- if the index is out of range (- index < 0 || index > size())
 
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listIteratorpublic ListIterator<E> listIterator() Returns a list iterator over the elements in this list (in proper sequence).The returned list iterator is fail-fast. - Specified by:
- listIteratorin interface- List<E>
- Overrides:
- listIteratorin class- AbstractList<E>
- Returns:
- a list iterator over the elements in this list (in proper sequence)
- See Also:
- listIterator(int)
 
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iteratorpublic Iterator<E> iterator() Returns an iterator over the elements in this list in proper sequence.The returned iterator is fail-fast. 
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subListpublic List<E> subList(int fromIndex, int toIndex) Returns a view of the portion of this list between the specifiedfromIndex, inclusive, andtoIndex, exclusive. (IffromIndexandtoIndexare equal, the returned list is empty.) The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa. The returned list supports all of the optional list operations.This method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a list can be used as a range operation by passing a subList view instead of a whole list. For example, the following idiom removes a range of elements from a list: list.subList(from, to).clear();Similar idioms may be constructed forindexOf(Object)andlastIndexOf(Object), and all of the algorithms in theCollectionsclass can be applied to a subList.The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.) - Specified by:
- subListin interface- List<E>
- Overrides:
- subListin class- AbstractList<E>
- Parameters:
- fromIndex- low endpoint (inclusive) of the subList
- toIndex- high endpoint (exclusive) of the subList
- Returns:
- a view of the specified range within this list
- Throws:
- IndexOutOfBoundsException- if an endpoint index value is out of range- (fromIndex < 0 || toIndex > size)
- IllegalArgumentException- if the endpoint indices are out of order- (fromIndex > toIndex)
 
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forEachpublic void forEach(Consumer<? super E> action) Description copied from interface:IterablePerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy. - Specified by:
- forEachin interface- Iterable<E>
- Parameters:
- action- The action to be performed for each element
- Throws:
- NullPointerException- if the specified action is null
 
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spliteratorpublic Spliterator<E> spliterator() Creates a late-binding and fail-fastSpliteratorover the elements in this list.The SpliteratorreportsSpliterator.SIZED,Spliterator.SUBSIZED, andSpliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values.- Specified by:
- spliteratorin interface- Collection<E>
- Specified by:
- spliteratorin interface- Iterable<E>
- Specified by:
- spliteratorin interface- List<E>
- Returns:
- a Spliteratorover the elements in this list
- Since:
- 1.8
 
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removeIfpublic boolean removeIf(Predicate<? super E> filter) Description copied from interface:CollectionRemoves 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.- Specified by:
- removeIfin interface- Collection<E>
- Parameters:
- filter- a predicate which returns- truefor elements to be removed
- Returns:
- trueif any elements were removed
- Throws:
- NullPointerException- if the specified filter is null
 
 
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