JavaFX Collection's ObservableList and ObservableMap

Collections in JavaFX are defined by the javafx.collections package, which consists of the following interfaces and classes:

Interfaces:

• ObservableList: A list that enables listeners to track changes when they occur

• ListChangeListener: An interface that receives notifications of changes to an ObservableList

• ObservableMap: A map that enables observers to track changes when they occur

• MapChangeListener: An interface that receives notifications of changes to an ObservableMap

Classes:

• FXCollections: A utility class that consists of static methods that are one-to-one copies of java.util.Collections methods

• ListChangeListener.Change: Represents a change made to an ObservableList

• MapChangeListener.Change: Represents a change made to an ObservableMap

Example of ObservableList

Here a standard List is first created. It is then wrapped with an ObservableList. A ListChangeListener is then registered, and will receive notification whenever a change is made on the ObservableList :

packageorg.attune.collection;

importjava.util.List;

importjava.util.ArrayList;

importjavafx.collections.ObservableList;

importjavafx.collections.ListChangeListener;

importjavafx.collections.FXCollections;

public class ObservableListDemo {

public static void main(String[] args)

{

List<String> list = new ArrayList<String>();

ObservableList<String>observableList = FXCollections.observableList(list);

observableList.addListener(new ListChangeListener() {

@Override

public void onChanged(ListChangeListener.Change change) {

System.out.println("Detected a change! ");

while (change.next()) {

System.out.println("Was added? " + change.wasAdded());

System.out.println("Was removed? " + change.wasRemoved());

}

}

});

observableList.add("a : item one");

System.out.println("Size: " + observableList.size()+observableList.toString());

list.add("d : item two");

System.out.println("Size: " + observableList.size()+observableList.toString());

observableList.add("f : item Three");

System.out.println("Size: " + observableList.size()+observableList.toString());

list.add("b : item four");

System.out.println("Size: " + observableList.size()+observableList.toString());

observableList.remove(1);

System.out.println("Size: " + observableList.size()+observableList.toString());

observableList.sort(null);

System.out.println("Size: " + observableList.size()+observableList.toString());

observableList.set(2, "c : item five");

System.out.println("Size: " + observableList.size()+observableList.toString());

}

}

Here is output of above program:

Detected a change!

Was added? true

Was removed? false

Size: 1[a : item one]

Size: 2[a : item one, d : item two]

Detected a change!

Was added? true

Was removed? false

Size: 3[a : item one, d : item two, f : item Three]

Size: 4[a : item one, d : item two, f : item Three, b : item four]

Detected a change!

Was added? false

Was removed? true

Size: 3[a : item one, f : item Three, b : item four]

Detected a change!

Was added? false

Was removed? false

Size: 3[a : item one, b : item four, f : item Three]

Detected a change!

Was added? true

Was removed? true

Size: 3[a : item one, b : item four, c : item five]

Example of ObservableMap

package org.attune.collection;
import java.util.Map;
import java.util.HashMap;
import javafx.collections.ObservableMap;
import javafx.collections.MapChangeListener;
import javafx.collections.FXCollections;

public class ObservableMapDemo {

public static void main(String[] args) {

Map<String,String> map = new HashMap<String,String>();

ObservableMap<String,String> observableMap = FXCollections.observableMap(map);
observableMap.addListener(new MapChangeListener() {
@Override
public void onChanged(MapChangeListener.Change change) {
System.out.println("Detected a change! ");
}
});

// Changes to the observableMap WILL be reported.
observableMap.put("key 1","value 1");
System.out.println("Size: "+observableMap.size() + observableMap.toString());

// Changes to the underlying map will NOT be reported.
map.put("key 2","value 2");
System.out.println("Size: "+observableMap.size()+ observableMap.toString());
// Changes to the observableMap WILL be reported.
observableMap.remove("key 1");
System.out.println("Size: "+observableMap.size() + observableMap.toString());
}
}

Here is the output:
Detected a change!
Size: 1{key 1=value 1}
Size: 2{key 2=value 2, key 1=value 1}
Detected a change!
Size: 1{key 2=value 2}

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