What's collection
a framework/architecture(a set of classes /interface) to store and manipulation group(single unit) of objcts |
sorting, searching, insert, delete, iterate etc. |
many interfaces: List, Set, Queue,Dequeue |
many classes: ArrayList,Vector, LinkedList,PriorityQueue,HashSet,TreeSet etc |
Collection framework hierarchy
iterable --> collection -->List,Queue/Deque,Set/SortedSet |
list->ArrayList,LinkedList,Vector <-Sack |
Queue ->PriorityQueue |
Deque ->ArrayDeque,LinkedList |
SortedSet->TreeSet |
Set->HashSet,LinkedHashSet |
Collection Methods
public boolean add(E e) |
append an item |
public boolean addAll(Collection<? extends E> c) |
addAll |
public boolean remove(Object element) |
remove 1 |
public boolean removeAll(Collection<?> c) |
removeAll |
default boolean removeIf(Predicate<? super E> filter) |
removeIf |
public boolean retainAll(Collection<?> c) |
retainAll |
public int size() |
size() |
public void clear() |
clear |
public boolean isEmpty() |
isEmpty |
public boolean contains(Object element) |
contains |
public boolean containsAll(Collection<?> c) |
containsAll |
public Iterator iterator() |
iterator |
public Object[] toArray() |
toArray |
public <T> T[] toArray(T[] a) |
toArray type |
public boolean equals(Object element) |
equals |
public int hashCode() |
hashcode |
default Stream<E> parallelStream() |
default Stream<E> stream() |
default Spliterator<E> spliterator() |
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Iterator interface
public boolean hasNext() |
public Object next() |
public void remove() |
enumeration hasMoreElement(), nextElement(), but no remove()
Iterable interface
top of collection |
Only one method: |
Iterator<T> iterator() |
return the iterator over the items of type T |
4 way to iterate |
1. iterator |
hasNext(), next() |
2. for loop |
size() |
3. for each loop |
4.lambda expression forEach() |
list.forEach(name->name.charAt(0)='h') |
mapAscii.forEach((key, value) |
can be used to iterate map |
List Interface
Duplicable |
ArrayList |
random access, add/remove expensive(shift),not ordered |
LinkedList |
sequence access,add/remove cheap(no shift), ordered |
Vector |
like ArrayList,but synchronized,more methods |
Stack |
extends Vector, LIFO, more methods |
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boolean push(),boolean peek(),boolean push(obj) |
Queue interface
FIFO |
first in first out |
Ordered list of item to be processed |
PriorityQueue |
no null item, ordered by priority |
Deque |
interface, doubled ended queue |
ArrayDeque |
add/remove from both end, faster than ArrayList and Stack |
Set
unordered |
no duplicate, at most one null |
Hashset |
LinkedListHashSet |
maintain insertion order, permit nulls |
SortedSet interface |
sorted ascending/decending/natual ordering |
TreeSet |
ascending order, faster access |
Java Collections
java.util.Collections |
Static methods |
max() |
min() |
sort() |
shuffle() |
binarySearch() |
copy() |
reverse() |
synchronizedCollection() |
disjoin(): split into 3 collection w/o commons |
Comparable and Comparator interfaces
Comparator |
equals(), Compare() |
Comparable |
compareTo() |
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Java Map
key value pairs |
not iterable |
NoSuchElementException |
ClassCastException |
NullPointerException |
UnsupportedOperationException |
Object put(Object k, Object v) |
add |
void putAll(Map m) |
addAll |
Object remove(Object k) |
remvoe |
Object get(Object k) |
get |
boolean containsKey(Object k) |
ContainsKey |
boolean containsValue(Object v) |
containsValue |
Set entrySet( ) |
value->set |
Set keySet( ) |
key->set |
Collection values( ) |
value->collection |
int size( ) |
size |
void clear( ) |
clear |
boolean isEmpty( ) |
isEmpty |
boolean equals(Object obj) |
equals |
int hashCode( ) |
hashcode |
iterate on map
No iterator |
1 for each loop |
for ( Map.Entry<String,String> e:myMap.entrySet()){} |
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for (String k:myMap.keySet()){} |
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for (String v:myMap.value()){} |
2 indrect iterator |
Oterator<Map.Entry<String,String>> itr=myMao.entrySet().iterator() |
3 stand for loop |
size() |
4 forEach(lambdas) |
myMap.foreach((k,v)->...) |
5 iterator on key |
set value myMap.get(key) |
not efficient, not practical |
HashMap,Treemap and Hashable
HashMap: |
unique key, dup values;allow null values and null keys |
TreeMap |
ordered object |
HashTable |
synchonized, no nulls |
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