java.util.Collection Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.util;
/**
* {@code Collection} is the root of the collection hierarchy. It defines operations on
* data collections and the behavior that they will have in all implementations
* of {@code Collection}s.
*
* All direct or indirect implementations of {@code Collection} should implement at
* least two constructors. One with no parameters which creates an empty
* collection and one with a parameter of type {@code Collection}. This second
* constructor can be used to create a collection of different type as the
* initial collection but with the same elements. Implementations of {@code Collection}
* cannot be forced to implement these two constructors but at least all
* implementations under {@code java.util} do.
*
* Methods that change the content of a collection throw an
* {@code UnsupportedOperationException} if the underlying collection does not
* support that operation, though it's not mandatory to throw such an {@code Exception}
* in cases where the requested operation would not change the collection. In
* these cases it's up to the implementation whether it throws an
* {@code UnsupportedOperationException} or not.
*
* Methods marked with (optional) can throw an
* {@code UnsupportedOperationException} if the underlying collection doesn't
* support that method.
*/
public interface Collection extends Iterable {
/**
* Attempts to add {@code object} to the contents of this
* {@code Collection} (optional).
*
* After this method finishes successfully it is guaranteed that the object
* is contained in the collection.
*
* If the collection was modified it returns {@code true}, {@code false} if
* no changes were made.
*
* An implementation of {@code Collection} may narrow the set of accepted
* objects, but it has to specify this in the documentation. If the object
* to be added does not meet this restriction, then an
* {@code IllegalArgumentException} is thrown.
*
* If a collection does not yet contain an object that is to be added and
* adding the object fails, this method must throw an appropriate
* unchecked Exception. Returning false is not permitted in this case
* because it would violate the postcondition that the element will be part
* of the collection after this method finishes.
*
* @param object
* the object to add.
* @return {@code true} if this {@code Collection} is
* modified, {@code false} otherwise.
*
* @throws UnsupportedOperationException
* if adding to this {@code Collection} is not supported.
* @throws ClassCastException
* if the class of the object is inappropriate for this
* collection.
* @throws IllegalArgumentException
* if the object cannot be added to this {@code Collection}.
* @throws NullPointerException
* if null elements cannot be added to the {@code Collection}.
*/
public boolean add(E object);
/**
* Attempts to add all of the objects contained in {@code Collection}
* to the contents of this {@code Collection} (optional). If the passed {@code Collection}
* is changed during the process of adding elements to this {@code Collection}, the
* behavior is not defined.
*
* @param collection
* the {@code Collection} of objects.
* @return {@code true} if this {@code Collection} is modified, {@code false}
* otherwise.
* @throws UnsupportedOperationException
* if adding to this {@code Collection} is not supported.
* @throws ClassCastException
* if the class of an object is inappropriate for this
* {@code Collection}.
* @throws IllegalArgumentException
* if an object cannot be added to this {@code Collection}.
* @throws NullPointerException
* if {@code collection} is {@code null}, or if it
* contains {@code null} elements and this {@code Collection} does
* not support such elements.
*/
public boolean addAll(Collection collection);
/**
* Removes all elements from this {@code Collection}, leaving it empty (optional).
*
* @throws UnsupportedOperationException
* if removing from this {@code Collection} is not supported.
*
* @see #isEmpty
* @see #size
*/
public void clear();
/**
* Tests whether this {@code Collection} contains the specified object. Returns
* {@code true} if and only if at least one element {@code elem} in this
* {@code Collection} meets following requirement:
* {@code (object==null ? elem==null : object.equals(elem))}.
*
* @param object
* the object to search for.
* @return {@code true} if object is an element of this {@code Collection},
* {@code false} otherwise.
* @throws ClassCastException
* if the object to look for isn't of the correct
* type.
* @throws NullPointerException
* if the object to look for is {@code null} and this
* {@code Collection} doesn't support {@code null} elements.
*/
public boolean contains(Object object);
/**
* Tests whether this {@code Collection} contains all objects contained in the
* specified {@code Collection}. If an element {@code elem} is contained several
* times in the specified {@code Collection}, the method returns {@code true} even
* if {@code elem} is contained only once in this {@code Collection}.
*
* @param collection
* the collection of objects.
* @return {@code true} if all objects in the specified {@code Collection} are
* elements of this {@code Collection}, {@code false} otherwise.
* @throws ClassCastException
* if one or more elements of {@code collection} isn't of the
* correct type.
* @throws NullPointerException
* if {@code collection} contains at least one {@code null}
* element and this {@code Collection} doesn't support {@code null}
* elements.
* @throws NullPointerException
* if {@code collection} is {@code null}.
*/
public boolean containsAll(Collection collection);
/**
* Compares the argument to the receiver, and returns true if they represent
* the same object using a class specific comparison.
*
* @param object
* the object to compare with this object.
* @return {@code true} if the object is the same as this object and
* {@code false} if it is different from this object.
* @see #hashCode
*/
public boolean equals(Object object);
/**
* Returns an integer hash code for the receiver. Objects which are equal
* return the same value for this method.
*
* @return the receiver's hash.
*
* @see #equals
*/
public int hashCode();
/**
* Returns if this {@code Collection} contains no elements.
*
* @return {@code true} if this {@code Collection} has no elements, {@code false}
* otherwise.
*
* @see #size
*/
public boolean isEmpty();
/**
* Returns an instance of {@link Iterator} that may be used to access the
* objects contained by this {@code Collection}. The order in which the elements are
* returned by the iterator is not defined. Only if the instance of the
* {@code Collection} has a defined order the elements are returned in that order.
*
* @return an iterator for accessing the {@code Collection} contents.
*/
public Iterator iterator();
/**
* Removes one instance of the specified object from this {@code Collection} if one
* is contained (optional). The element {@code elem} that is removed
* complies with {@code (object==null ? elem==null : object.equals(elem)}.
*
* @param object
* the object to remove.
* @return {@code true} if this {@code Collection} is modified, {@code false}
* otherwise.
* @throws UnsupportedOperationException
* if removing from this {@code Collection} is not supported.
* @throws ClassCastException
* if the object passed is not of the correct type.
* @throws NullPointerException
* if {@code object} is {@code null} and this {@code Collection}
* doesn't support {@code null} elements.
*/
public boolean remove(Object object);
/**
* Removes all occurrences in this {@code Collection} of each object in the
* specified {@code Collection} (optional). After this method returns none of the
* elements in the passed {@code Collection} can be found in this {@code Collection}
* anymore.
*
* @param collection
* the collection of objects to remove.
* @return {@code true} if this {@code Collection} is modified, {@code false}
* otherwise.
*
* @throws UnsupportedOperationException
* if removing from this {@code Collection} is not supported.
* @throws ClassCastException
* if one or more elements of {@code collection}
* isn't of the correct type.
* @throws NullPointerException
* if {@code collection} contains at least one
* {@code null} element and this {@code Collection} doesn't support
* {@code null} elements.
* @throws NullPointerException
* if {@code collection} is {@code null}.
*/
public boolean removeAll(Collection collection);
/**
* Removes all objects from this {@code Collection} that are not also found in the
* {@code Collection} passed (optional). After this method returns this {@code Collection}
* will only contain elements that also can be found in the {@code Collection}
* passed to this method.
*
* @param collection
* the collection of objects to retain.
* @return {@code true} if this {@code Collection} is modified, {@code false}
* otherwise.
* @throws UnsupportedOperationException
* if removing from this {@code Collection} is not supported.
* @throws ClassCastException
* if one or more elements of {@code collection}
* isn't of the correct type.
* @throws NullPointerException
* if {@code collection} contains at least one
* {@code null} element and this {@code Collection} doesn't support
* {@code null} elements.
* @throws NullPointerException
* if {@code collection} is {@code null}.
*/
public boolean retainAll(Collection collection);
/**
* Returns a count of how many objects this {@code Collection} contains.
*
* @return how many objects this {@code Collection} contains, or Integer.MAX_VALUE
* if there are more than Integer.MAX_VALUE elements in this
* {@code Collection}.
*/
public int size();
/**
* Returns a new array containing all elements contained in this {@code Collection}.
*
* If the implementation has ordered elements it will return the element
* array in the same order as an iterator would return them.
*
* The array returned does not reflect any changes of the {@code Collection}. A new
* array is created even if the underlying data structure is already an
* array.
*
* @return an array of the elements from this {@code Collection}.
*/
public Object[] toArray();
/**
* Returns an array containing all elements contained in this {@code Collection}. If
* the specified array is large enough to hold the elements, the specified
* array is used, otherwise an array of the same type is created. If the
* specified array is used and is larger than this {@code Collection}, the array
* element following the {@code Collection} elements is set to null.
*
* If the implementation has ordered elements it will return the element
* array in the same order as an iterator would return them.
*
* {@code toArray(new Object[0])} behaves exactly the same way as
* {@code toArray()} does.
*
* @param array
* the array.
* @return an array of the elements from this {@code Collection}.
*
* @throws ArrayStoreException
* if the type of an element in this {@code Collection} cannot be
* stored in the type of the specified array.
*/
public T[] toArray(T[] array);
}