Java - Streams: Difference between revisions
Line 56: | Line 56: | ||
===Remove by Index=== | ===Remove by Index=== | ||
A Naive Approach to Removing Elements Corresponding to a Set of Index Values | 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 | //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++) { | for (int i = 0; i < deleteIndices.length; i++) { | ||
Line 62: | Line 62: | ||
} | } | ||
//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--) { | for (int i = deleteIndices.length - 1; i >= 0; i--) { | ||
myList.remove(deletedIndices[i]); | myList.remove(deletedIndices[i]); | ||
} | } | ||
</source> | |||
=A voir= | =A voir= | ||
* Parallel stream | * Parallel stream |
Revision as of 17:33, 18 October 2019
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>
A voir
- Parallel stream