JavaFXObservableList

JavaFXObservableList

In JavaFX, collections are defined by the package known as javafx.collections that contains different interfaces such as ObservableList, ListChangeListener, ObservableMap ,MapChangeListener, and classes such as FXCollections, ListChangeListener.Change, MapChangeListener.Change etc. In this article, we will be focusing on the list known as ObservableList that permits tracking the changes when occurred. ListChangeListener.Change is a class that denotes the change that has been made to an ObservableList. First, we will see how to declare an ObservableList in JavaFX.

Declaration

Below is the declaration of ObservableList in JavaFX.

public interface ObservableList< E> extends List< E>, Observable

Methods

Following are the different methods of ObservableList in JavaFX.

1. addListener

   Syntax:

   void addListener(ListChangeListener li)

   Description:

   A listener li will be added to the observable list.

   Parameter:

   li, the listener that listens to the changes in the list.

2. removeListener

   Syntax:

   void removeListener(ListChangeListener li)

   Description:

   A listener li will be removed from the observable list. If it is not available, nothing will happen.

   Parameter:

   li, the listener that has to be removed.

3. addAll

   Syntax:

   boolean addAll(E… el)

   Description:

   A suitable method for the var-arg addition of elements.

   Parameter:

   el, elements that have to be added.

   Return Value:

   true, which is mentioned by Collection.add(E)

4. setAll

   Syntax:

   boolean setAll (E… el)

   Description:

   A suitable method for var-arg addition of elements after clearing the ObservableList.

   Parameter:

   el, elements that have to be set.

   Return Value:

   true, which is mentioned by Collection.add(E)

5. setAll

   Syntax:

   boolean setAll (Collection c)

   Description:

   A suitable method for adding all the elements from the collection after clearing the ObservableList.

   Parameter:

   c, the collection that contains elements that have to be added to the list.

   Return Value:

   true, which is mentioned by Collection.add(E)

6. removeAll

   Syntax:

   boolean removeAll (E… el)

   Description:

   A suitable method for var-arg removal of elements.

   Parameter:

   el, elements that have to be removed.

7. retainAll

   Syntax:

   boolean retainAll (E… el)

   Description:

   A suitable method for var-arg retaining of elements.

   Parameter:

   el, elements that have to be retained.

   Return Value:

   true if the ObservableList is changed due to calling this method.

8. remove

   Syntax:

   void remove(int from, int to)

   Description:

   Similar to sublist(from, to).clear(). ObservableList used this method for the same.

   Parameter:

   from, which is the starting of the range that has to be removed, and to, which is the ending of the range that has to be removed,

9. filtered

   Syntax:

   default FilteredList< E> filtered(Predicate< E> pr)

   Description:

   A FilteredList wrapper is created for this list by using the mentioned predicate.

   Parameter:

   pr, a predicate that has to be used.

   Return Value:

   A new filtered list.

10. sorted

    Syntax:

    default SortedList< E> sorted( Comparator< E> c)

    Description:

    A SortedList wrapper is created for this list by using the mentioned comparator.

    Parameter:

    c, a comparator that has to be used. If natural order, then null.

    Return Value:

    A new sorted list.

11. sorted

    Syntax:

    default SortedList< E> sorted( )

    Description:

    A SortedList wrapper is created for this list by natural ordering.

    Return Value:

    A new sorted list.

Examples of JavaFXObservableList

Now, we will see a few examples of ObservableList in JavaFX.

Example #1

JavaFX program to demonstrate ObservableList that consists of integer type elements.

Code:

//sample program to demonstrate the working of ObservableList
import java.util.List;
import java.util.ArrayList;
import javafx.collections.ObservableList;
import javafx.collections.ListChangeListener;
import javafx.collections.FXCollections;
//main class
public class ObservableListSample {
//main method
public static void main(String[] args)
{
//create a list of integer type
List< Integer> li = new ArrayList< Integer>();
//create an observable list
ObservableList< Integer>oli = FXCollections.observableList(li);
//add listener method
oli.addListener(new ListChangeListener() {
@Override
//onChanged method
public void onChanged(ListChangeListener.Change c) {
System.out.println("Hey, a change occured. . .  ");
}
});
//add an item to the observable List
oli.add(22);
System.out.println("Size of the observable list is: " + oli.size() );
li.add(44);
System.out.println("Size of the observable list is: " + oli.size());
oli.add(66);
System.out.println("Size of the observable list is: " + oli.size());
}
}

Example #2

JavaFX program to demonstrate ObservableList that consists of string type elements.

Code:

//sample program to demonstrate the working of ObservableList
import java.util.List;
import java.util.ArrayList;
import javafx.collections.ObservableList;
import javafx.collections.ListChangeListener;
import javafx.collections.FXCollections;
//main class
public class ObservableListSample {
//main method
public static void main(String[] args)
{
//create a list of string type
List< String> li = new ArrayList< String>();//create an observable list
ObservableList< String>oli = FXCollections.observableList(li);
//add listener method
oli.addListener(new ListChangeListener() {
@Override
//onChanged method
public void onChanged(ListChangeListener.Change c) {
System.out.println("Hey, a change occured. . .  ");
//check
while (c.next()) {
//if anything was added
System.out.println("Hey, anything added ? " + c.wasAdded());
System.out.println("Hey, anything removed ?  " + c.wasRemoved());
}
}
});
//add an item to the observable List
oli.add("This is item 1");
System.out.println("Size of the observable list is: " + oli.size() + oli.toString());
li.add("This is item 2" );
System.out.println("Size of the observable list is: " + oli.size() + oli.toString());
oli.add("This is item 3");
System.out.println("Size of the observable list is: " + oli.size() + oli.toString());
li.add("This is item 4");
System.out.println("Size of the observable list is: " + oli.size() + oli.toString());
//remove
oli.remove(1);
System.out.println("Size of the observable list is: " + oli.size()+oli.toString());
oli.sort(null);
System.out.println("Size of the observable list is: " + oli.size()+oli.toString());
oli.set(2, "This is item 5");
System.out.println("Size of the observable list is: " + oli.size()+oli.toString());
}
}

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