Java Notes-9

標籤：java   collection   

Summary: introduce the collection feature of Java. includes Set. List and Queue

-Collection interface only define some basic common functions for all kinds of collections, includs: 

 boolean add(e), remove(e), contains(e) , 

 int size(), 

-collection can easily convert ro array as the example bellow:

public Object[] toArray

Collection <String> mycollection;String[] myStrings = mycollection.toArray(new String[0]);

-Iterator very often used in Java as a squencial access of elements

E next() //get next element

boolean hasNext() //in case of non-last element, rteturn true

Example:

//Pirnt all the elements of one collection

 

remove() removes the most recent obj by next()

-Special for loop for collection:

.

-Set collection: duplicate not allowed

 List collection: elements in specific order

 Queue collection is working as buffer

 Set : sortedSet, Java7 added NavigableSet, in which the add method can find most closest value to target then fulfil the adding

 List similar to array, but can operate eaily on position of element

 

public void add(int index, E element);public void remove(int index);public E get(int index);public Object set(int index, E element);

-Queue can be FIFO or LIFO

boolean offer(E element)//place the element into the queue, but only return faulse instead of throw an exceptionE poll // removes element at head of the queue, in case of failure return null instead of throwing exceptionE peek()//return head without removing

//Java 7 added Dequeue, which means can operate from 2 ends of the queue, (head or tial). corresponding method changed as:offerlast();pollfirst();polllast();peelfirst();peeklast();

-BlockingQueue

Enhance the capablity of timed wait, so that can adapt to multipul thread access.

public boolean offer( E element, long time, TimeUnit units )

This method attempts to place the element into the queue, just like the method of
the base  Queue interface, but blocks for up to the specified period of time as it waits
for space to become available.

public E poll( long time, timeUnit unit )

This method attempts to remove the element at the head of the queue, just like the
method of the base  Queue interface, but blocks for up to the specified period of time
as it waits for an element to become available.

public E take()

This method retrieves the element at the head of the queue, blocking if necessary
until one becomes available.

public void put( E element )

This method adds an element to the queue, blocking if necessary until space be‐
comes available.

Next: Map interface...

  

Java Notes-9