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COLLECTIONs FRAMEWORK
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CẤU TRÚC DỮ LIỆU
DATA STRUCTURES
[214441]
Nguyễn Xuân Vinh
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Introduction to Collections
A collection — sometimes called a container — is simply an
object that groups multiple elements into a single unit.
Collections are used to store, retrieve, manipulate, and
communicate aggregate data.
Represent data items that form a natural group, such as:
A poker hand (a collection of cards)
A mail folder (a collection of letters)
A telephone directory (a mapping of names to phone numbers)
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What is a Collections Framework
A collections framework is a unified architecture for representing
and manipulating collections.
All collections frameworks contain the following:
Interfaces: These are abstract data types that represent
collections
Implementations: These are the concrete implementations of the
collection interfaces.
Algorithms: These are the methods that perform useful
computations, such as searching and sorting
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Collections Interface
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Collections Implementations
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Collections Implementations
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Collection Implementations
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Concrete Classes: Collection
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Concrete Class: MAP
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Collections Comparision
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1) Collection Interface:Traversing Collections
There are two ways to traverse collections:
(1) with the for-each construct
for (Object o : collection)
System.out.println(o);
(2) by using Iterators.
Iterator<T> iterator = collection.iterator();
while(iterator.hasNext()) {
System.out.println(iterator.next());
}
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2) Collection Interface: Bulk Operations
containsAll — returns true if the target Collection contains all of
the elements in the specified Collection.
addAll — adds all of the elements in the specified Collection to
the target Collection.
removeAll — removes from the target Collection all of its
elements that are also contained in the specified Collection.
retainAll — removes from the target Collection all its elements
that are not also contained in the specified Collection. That is, it
retains only those elements in the target Collection that are also
contained in the specified Collection.
clear — removes all elements from the Collection.
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3) Collection Interface: Array Operations
The toArray methods are provided as a bridge between collections
and older APIs that expect arrays on input.
For example, suppose that c is a Collection:
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Object[] a = c.toArray();
String[] a = c.toArray(new String[0]);
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public interface Set<E> extends Collection<E> {
// Basic operations
int size();
boolean isEmpty();
boolean contains(Object element);
// optional
boolean add(E element);
// optional
boolean remove(Object element);
Iterator<E> iterator();
// Bulk operations
boolean containsAll(Collection<?> c);
// optional
boolean addAll(Collection<? extends E> c);
// optional
boolean removeAll(Collection<?> c);
// optional
boolean retainAll(Collection<?> c);
// optional
void clear();
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Set Interface
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// Array Operations
Object[] toArray();
<T> T[] toArray(T[] a);
}
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public class FindDups {
public static void main(String[] args) {
Set<String> s = new HashSet<String>();
for (String a : args)
if (!s.add(a))
System.out.println("Duplicate detected: " + a);
System.out.println(s.size() + " distinct words: " + s);
}
}
Duplicate detected: i
4 distinct words: [i, left, saw, came]
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Run:
java FindDups i came i saw i left
Output produced:
Duplicate detected: i
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1) Set Interface: Basic Operations
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2) Set Interface: Bulk Operations
s1.containsAll(s2) — returns true if s2 is a subset of s1. (s2 is a
subset of s1 if set s1 contains all of the elements in s2.)
s1.addAll(s2) — transforms s1 into the union of s1 and s2. (The
union of two sets is the set containing all of the elements
contained in either set.)
s1.retainAll(s2) — transforms s1 into the intersection of s1 and
s2. (The intersection of two sets is the set containing only the
elements common to both sets.)
s1.removeAll(s2) — transforms s1 into the (asymmetric) set
difference of s1 and s2. (For example, the set difference of s1
minus s2 is the set containing all of the elements found in s1 but
not in s2.)
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HỎI ĐÁP
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List Interface
A List is an ordered Collection (sometimes called a sequence).
Lists may contain duplicate elements. In addition to the operations
inherited from Collection, the List interface includes operations
for the following:
Positional access — manipulates elements based on their
numerical position in the list
Search — searches for a specified object in the list and returns its
numerical position
Iteration — extends Iterator semantics to take advantage of the
list's sequential nature
Range-view — performs arbitrary range operations on the list.
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public interface List<E> extends Collection<E> {
// Positional access
E get(int index);
// optional
E set(int index, E element);
// optional
boolean add(E element);
// optional
void add(int index, E element);
// optional
E remove(int index);
// optional
boolean addAll(int index, Collection<? extends E> c);
// Search
int indexOf(Object o);
int lastIndexOf(Object o);
// Iteration
ListIterator<E> listIterator();
ListIterator<E> listIterator(int index);
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List Interface
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// Range-view
List<E> subList(int from, int to);
}
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List Interface: Interators
public interface ListIterator<E> extends Iterator<E> {
boolean hasNext();
E next();
boolean hasPrevious();
E previous();
int nextIndex();
int previousIndex();
void remove(); //optional
void set(E e); //optional
void add(E e); //optional
}
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Queue Interface
public interface Queue<E> extends Collection<E> {
E element();
boolean offer(E e);
E peek();
E poll();
E remove();
}
public interface Map<K,V> {
// Basic operations
V put(K key, V value);
V get(Object key);
V remove(Object key);
boolean containsKey(Object key);
boolean containsValue(Object value);
int size();
boolean isEmpty();
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Map Interface
// Bulk operations
void putAll(Map<? extends K, ? extends V> m);
void clear();
// Collection Views
public Set<K> keySet();
public Collection<V> values();
public Set
entrySet();
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// Interface for entrySet elements
public interface Entry {
K getKey();
V getValue();
V setValue(V value);
}
}