I was wondering if there is a data structure that acts like an OberservableCollection almost like in C# that is able to take a certain type.
ex:
In C# i am able to say..
开发者_开发问答ObservableCollection<Beer> Beer = new ObservableCollection<Beer>();
Beer.add("Bud"); <br>
Beer.add("Coors");
Assuming that the class Beer is made and we can change the alcohol content so that
Beer[1].content = 5;
I was wondering if anyone knows if there is such a data structure/s that work as well with Java.
I am a C# programmer, not much of a Java programmer so just wondering. Also, it has to be able to take in a custom type, not generic.
org.apache.commons.events.observable Class ObservableCollection
Observable data structures (ObservableList, ObservableMap, etc) are included in Oracle Java 7u6+ as part of the JavaFX project. A corresponding library for OpenJDK is provided by the OpenJFX project.
Here is a tutorial on using JavaFX collections.
And some sample code for using a JavaFX observable list from the linked tutorial:
import java.util.List;
import java.util.ArrayList;
import javafx.collections.*;
public class CollectionsDemo {
public static void main(String[] args) {
// Use Java Collections to create the List.
List<String> list = new ArrayList<String>();
// Now add observability by wrapping it with ObservableList.
ObservableList<String> observableList = FXCollections.observableList(list);
observableList.addListener(new ListChangeListener() {
@Override public void onChanged(ListChangeListener.Change change) {
System.out.println("Detected a change! ");
}
});
// Changes to the observableList WILL be reported.
// This line will print out "Detected a change!"
observableList.add("item one");
// Changes to the underlying list will NOT be reported
// Nothing will be printed as a result of the next line.
list.add("item two");
System.out.println("Size: "+observableList.size());
}
}
If you want to Observe your lists, i.e. be notified when list changes, you can use Glazed Lists.
If you just want to modify objects stored in your lists, you can get your objects by using List.get(int index), or by iterating the list.
If you want to automatically create Beer objects when storing Strings into the list, you'll probably need to write your own simple list wrapper.
JavaFX now has ObservableList that match your needs, in the case that you don't want to depend on JavaFX - here is a class that I wrote a while ago that can be used instead.
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
/**
*
* @author bennyl
*/
public class ObservableList<T> implements List<T> {
private List<T> wrapped;
private LinkedList<Listener<T>> listeners = new LinkedList<>();
public ObservableList(List wrapped) {
this.wrapped = wrapped;
}
public void addListener(Listener l) {
listeners.add(l);
}
public void removeListener(Listener l) {
listeners.remove(l);
}
@Override
public int size() {
return wrapped.size();
}
@Override
public boolean isEmpty() {
return wrapped.isEmpty();
}
@Override
public boolean contains(Object o) {
return wrapped.contains(o);
}
@Override
public Iterator<T> iterator() {
final Iterator<T> iterator = wrapped.iterator();
return new Iterator<T>() {
T current = null;
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public T next() {
return current = iterator.next();
}
@Override
public void remove() {
iterator.remove();
fireRemoved(current);
}
};
}
private void fireRemoved(T... items) {
fireRemoved(Arrays.asList(items));
}
@Override
public Object[] toArray() {
return wrapped.toArray();
}
@Override
public <T> T[] toArray(T[] a) {
return wrapped.toArray(a);
}
@Override
public boolean add(T e) {
if (wrapped.add(e)) {
fireAdded(e);
return true;
} else {
return false;
}
}
@Override
public boolean remove(Object o) {
if (wrapped.remove(o)) {
fireRemoved((T) o);
return true;
}
return false;
}
@Override
public boolean containsAll(Collection<?> c) {
return wrapped.containsAll(c);
}
@Override
public boolean addAll(Collection<? extends T> c) {
if (wrapped.addAll(c)) {
fireAdded(c);
return true;
}
return false;
}
@Override
public boolean addAll(int index, Collection<? extends T> c) {
if (wrapped.addAll(index, c)) {
fireAdded(c);
}
return false;
}
@Override
public boolean removeAll(Collection<?> c) {
if (wrapped.removeAll(c)) {
fireRemoved((Collection<? extends T>) c);
return true;
}
return false;
}
@Override
public boolean retainAll(Collection<?> c) {
if (wrapped.retainAll(c)) {
fireStracturalChange();
}
return false;
}
@Override
public void clear() {
wrapped.clear();
fireStracturalChange();
}
@Override
public boolean equals(Object o) {
return wrapped.equals(o);
}
@Override
public int hashCode() {
return wrapped.hashCode();
}
@Override
public T get(int index) {
return wrapped.get(index);
}
@Override
public T set(int index, T element) {
T old = wrapped.set(index, element);
fireRemoved(old);
fireAdded(element);
return old;
}
@Override
public void add(int index, T element) {
wrapped.add(index, element);
fireAdded(element);
}
@Override
public T remove(int index) {
T old = wrapped.remove(index);
fireRemoved(old);
return old;
}
@Override
public int indexOf(Object o) {
return wrapped.indexOf(o);
}
@Override
public int lastIndexOf(Object o) {
return wrapped.lastIndexOf(o);
}
@Override
public ListIterator<T> listIterator() {
return wrapped.listIterator();
}
@Override
public ListIterator<T> listIterator(int index) {
return wrapped.listIterator(index);
}
@Override
public List<T> subList(int fromIndex, int toIndex) {
return wrapped.subList(fromIndex, toIndex);
}
private void fireRemoved(Collection<? extends T> asList) {
for (Listener<T> l : listeners) {
l.onItemsRemoved(this, asList);
}
}
private void fireAdded(T... e) {
fireAdded(Arrays.asList(e));
}
private void fireAdded(Collection<? extends T> asList) {
for (Listener<T> l : listeners) {
l.onItemsAdded(this, asList);
}
}
private void fireStracturalChange() {
for (Listener<T> l : listeners) {
l.onStracturalChange(this);
}
}
public static interface Listener<T> {
void onItemsAdded(ObservableList<T> source, Collection<? extends T> items);
void onItemsRemoved(ObservableList<T> source, Collection<? extends T> items);
void onStracturalChange(ObservableList<T> source);
}
}
There isn't at least in Java Collections api
http://download-llnw.oracle.com/javase/1.5.0/docs/guide/collections/designfaq.html#27
You can create an wrapper or proxy
You can consider using the java.util.Observable class, here is an example :
public class Try extends Observable{
private static List<String> list = new ArrayList<String>();
private static Try observableObj = new Try();
public static List<String> getList(){
observableObj.setChanged();
observableObj.notifyObservers();
return list;
}
public static void main(String[] args) throws RemoteException {
Try2 observer1 = new Try2();
Try2 observer2 = new Try2();
observableObj.addObserver(observer1);
observableObj.addObserver(observer2);
System.out.println(getList().isEmpty());
}
}
class Try2 implements Observer{
@Override
public void update(Observable arg0, Object arg1) {
System.out.println(this.toString()+" has been notified");
}
}
In this way every time the ArrayList gets accessed the two observers get notified.
Sure, you can do this. If you had a class called Soda, you could do:
List<Soda> sodas = new ArrayList<Soda>();
sodas.add(new Soda("Coke"));
sodas.add(new Soda("Sprite"));
Then you could do
sodas.get(1).setSugar(255);
精彩评论