Java - Streams

Collections

Main Methods

<source lang="Java"> - add(Object o) //Adds the specified object to the collection. - remove(Object o) //Removes the specified object from the collection. - clear() //Removes all elements from the collection. - size() //Returns an integer that indicates how many elements are currently in the collection. - iterator() //Returns an object that can be used to retrieve references to the elements in the collection. </source>

Samples

Print all Students name

<source lang="Java"> Student student; Iterator iterator = collection.iterator(); while (iterator.hasNext()) {

   student = (Student)(iterator.next());
   System.out.println(student.getFullName());

} </source>

Get a Student

<source lang="Java"> Student student = getNextStudent(); while (student != null) {

   collection.add(student);

} </source>

Iteration Without Generics Often Requires Casting

<source lang="Java"> Student student; Iterator iterator = collection.iterator(); while (iterator.hasNext()) {

   student = (Student)(iterator.next());
   System.out.println(student.getFullName());

} </source>

Autoboxing

is the process of performing the encapsulation before a primitive is stored in a collection, and the following is an example of how this can improve your code: <source lang="Java"> Random random = new Random(); Collection<Integer> collection = new ArrayList<Integer>(); for (int i = 0; i < 10; i++) {

   collection.add(random.nextInt());

} </source>

Unboxing

is the process of extracting the primitive value from its corresponding wrapper object when retrieving data from a collection: <source lang="Java"> int total = 0; Iterator<Integer> iterator = collection.iterator(); while (iterator.hasNext()) {

   total += iterator.next();

} </source>

Remove by Index

A Naive Approach to Removing Elements Corresponding to a Set of Index Values <source lang="java"> //as soon as you remove the first entry, the other indices in the array effectively become invalid because they no longer refer to the same elements for (int i = 0; i < deleteIndices.length; i++) {

  myList.remove(deleteIndices[i]);

}

//An easy way to address this problem is to simply traverse the index list in reverse order for (int i = deleteIndices.length - 1; i >= 0; i--) {

   myList.remove(deletedIndices[i]);

} </source>

Queue

Main Methods

<source lang="Java"> - element() Returns a reference to the head element without removing it, throwing an exception if the queue is empty. - peek() //Returns a reference to the head element without removing it, returning null if the queue is empty. - offer() //Adds an element to the queue. Some implementations may reject the addition, in which case a value of false is returned. - remove() //Retrieves a reference to the head element and removes it from the queue, throwing an exception if the queue is empty. - poll() //Retrieves a reference to the head element and removes it from the queue, returning null if the queue is empty. </source>

A voir

• Parallel stream