class UnfairContainer<T> implements Comparable<UnfairContainer>
{
private ArrayList<T> array = new ArrayList<T>();
public void sort()
{
Collections.sort(array);
}
public int compareTo(UnfairContainer o)
{
}
}
So i have my class that implements comparable but when i try to create the sort method that calls Collections.sort(), it gives me an error that says i can't call collection sort with an ArrayList . Can anyone help? and help me with my compareTo method, i'm stuck on how i'm suppose to compare each element within my ArrayList
The problem is that the list is not guaranteed to be sort-able. This is because with your current setup, T could be anything- including a class that does not implement Comparable and hence cannot be sorted by Collections. The type signature of Collections.sort() reflects this:
public static <T extends Comparable<? super T>> void sort(List<T> list);
To fix this, you need to put an upper bound on T to ensure that it is sort-able:
class UnfairContainer<T extends Comparable<T> >
implements Comparable<UnfairContainer<T> >
{
...
The T extends Comparable<T> means that T must be a class that implements Comparable. This lets Collections know that the ArrayList can be sorted, and everything works.
For more information, please refer to the java trail on bounded wildcards in generics
Related
In my project, I'd like to get all the range class related to the given class by an restricted(somevaluefrom or allvalues from) objectproperties. I can get the restricted subclassofAxioms expressions including the given class, but how can I get the range class in these expressions? In other word, how can I get all the related classes to the given class excluding inherited subclass.
For example:
public static void printSubClassOfAxioms(OWLOntology ontology,OWLReasoner reasoner,OWLClass owlClass){
for(OWLSubClassOfAxiom ax:ontology.getSubClassAxiomsForSubClass(owlClass)){
OWLClassExpression expression=ax.getSuperClass();
System.out.println(ax);
System.out.println(expression);
}
}
The results are:
SubClassOf(<#FourCheesesTopping> <#CheeseTopping>)
SubClassOf(<#FourCheesesTopping> ObjectSomeValuesFrom(<#hasSpiciness> <#Mild>))
SubClassOf(<#FourCheesesTopping> ObjectAllValuesFrom(<#hasCountryOfOrigin> #Country>))
How can I just get the range classes #Country and #Mild
Thank you for your attention!
Write an OWLObjectVisitor and override the visit(OWL... Type) for the restrictions you're interested in. At that point,
type.getFiller()
will yield the class you're after.
Examples are in the documentation: https://github.com/owlcs/owlapi/wiki/Documentation
public class RestrictionVisitor extends OWLClassExpressionVisitor {
#Override
public void visit(#Nonnull OWLObjectSomeValuesFrom ce) {
// This method gets called when a class expression is an existential
// (someValuesFrom) restriction and it asks us to visit it
}
}
I've encountered several serializable exceptions, and I did some searching on Flink's internet and doc; there are some famous solutions like transient, extends Serializable etc. Each time the origin of exception is very clear, but in my case, i am unable to find where exactly it is not serialized.
Q: How should i debug this kind of Exception?
A.scala:
class executor ( val sink: SinkFunction[List[String]] {
def exe(): Unit = {
xxx.....addSink(sinks)
}
}
B.scala:
class Main extends App {
def createSink: SinkFunction[List[String]] = new StringSink()
object StringSink {
// static
val stringList: List[String] = List()
}
// create a testing sink
class StringSink extends SinkFunction[List[String]] {
override def invoke(strs: List[String]): Unit = {
// add strs into the variable "stringList" of the compagin object StringSink
}
}
new executor(createSink()).exe()
// then do somethings with the strings
}
The exception is:
The implementation of the SinkFunction is not serializable. The
object probably contains or references non serializable fields.
Two suspicious points that I found:
The instance of StringSink is passed into another file.
In the class of StringSink, it uses a static variable stringList
of its compagin object.
I faced similar problems. It used to take longtime to find out what member/object is not serializable. The exception logs are not really helpful.
What helped me is the following JVM option, which enables more details in exception trace.
Enable this option...
-Dsun.io.serialization.extendedDebugInfo=true
My first guess would be the you don't have a no argument constructor in StringSink
Rules for POJO types Clipped from here
Flink recognizes a data type as a POJO type (and allows “by-name” field referencing) if the following conditions are fulfilled:
The class is public and standalone (no non-static inner class)
The class has a public no-argument constructor
All non-static, non-transient fields in the class (and all superclasses) are either public (and non-final) or have a public getter- and a setter- method that follows the Java beans naming conventions for getters and setters.
Just add a no argument constructor and try again
class StringSink extends SinkFunction[List[String]] {
public StringSink() {
}
#override def invoke(strs: List[String]): Unit = {
// add strs into the variable "stringList" of the compagin object StringSink
}
}
I implemented my custom ArrayList using a resizeable Array, and I would like to unit test my add method to check if the right value getting inserted to the right position. My add method looks like this:
public class MyArrayList<T> implements ArrayListInterface {
private int max=20;
private int index = 0;
private int[] a = new int[max];
#Override
public void add(int value) {
if(index>max-1) {
resize();
}
a[index] = value;
index++;
}
I am aware, I could just make my method boolean and check what the method returns, but I would like to check that the right value added to the right position. My problem is that my Array is private, and that way it is only possible to reach its value through a getter. Is it a good solution to make a getter for my Array, and compare that to the actual result of the test, or what would be the best solution to test this method?
I have checked couple of other stackoverflow questions in the same topic, but I couldn't find any solution for my problem.
Add a get() (get(position), getLast(), etc.) method to your class and test using this method. Unit tests should exercise the class through its interfaces, without caring about the internal implementation. Any other class that will interact with your MyArrayList will do so through add() and get().
I have to develop a custom collection of objects. The reason is two fold, I need to be able to assign an internal name to the collection and the collection also needs to implement some abstract methods to be treated like any other entity that I have.
So I created an EntityList class. Below is a snippet of the class. It contains a id and a list of entities, plus a bunch of methods. My question is this, so far I have put in the list management methods that I require, such as Add, Insert, Remove and Clear. If you have an EntityList reference called myEntityList you could perform something like myEntityList.Add(newEntity). I do like this approach, but really these methods are just handing off the work to the list. I could also not implement any of these methods and you could perform the same action as above by using myEntityList.Items.Add(newEntity). However, here you are directly accessing a method of a property of the object. I wanted to remove the Items property altogether, however I often need to iterate through the list using a foreach and for that I need access to the actual list.
Here is my class definition, it does not have the overrides to the abstact methods included.
class EntityList
{
String entityId;
List<EntityBase> _entities;
public EntityList()
{
_entities = new List<EntityBase>();
}
public List<EntityBase> Items
{
get { return _entities; }
//set { _entities = value; }
}
public void Add(EntityBase entity)
{
_entities.Add(entity);
}
public void Insert(int index, EntityBase entity)
{
_entities.Insert(index, entity);
}
public void Remove(EntityBase entity)
{
_entities.Remove(entity);
}
public void Clear()
{
_entities.Clear();
}
}
Am I violating some cardinal rules here? How should I manage the list when it is a member of another class?
Just inherit from List<EntityBase> then you won't need to redeclare and implement the list methods.
i.e.
class EntityList : List<EntityBase>
{
String entityId;
//add your extra methods.
}
you should make your class implement IList<EntityBase> (or at the very least, IEnumerable<EntityBase>) this way, you can treat it just like a "normal" list. Before you do this, though, you should probably read the documentation and decide which is best for your needs.
MSDN on IList is here
MSDN on IEnumerable is here
Like java, I want to create a method that accepts an array list of particular object type.
In java:
public void addStudents(List<Student> students) {
...
}
In actionscript
public function addStudents(students:ArrayCollection):void {
.....
}
Here I want to have public function addStudents(students:ArrayCollection).
Thanks
If you have a Student object and publish for FP10 you can use the Vector object.
public function addStudents(students:Vector.<Student>):void {}
For further information: http://help.adobe.com/en_US/AS3LCR/Flash_10.0/Vector.html
As far as i know, AS has no template-like generics. But you can extend ArrayCollection into something like StudentArrayCollection with more rigid type check inside.