Add Listeners.add(int, T) method to insert listeners at specified position

Author: tpietzsch

src/main/java/org/scijava/listeners/Listeners.java

@@ -5,15 +5,15 @@
 import java.util.function.Consumer;
 
 /**
- * A set of listeners of type {@code T}.
+ * An ordered set of listeners of type {@code T}.
  *
  * @param <T>
  *            listener type
  */
 public interface Listeners< T >
 {
 	/**
-	 * Add a listener to this set.
+	 * Add a listener to the end of this set.
 	 *
 	 * @param listener
 	 *            the listener to add.
@@ -22,6 +22,19 @@ public interface Listeners< T >
 	 */
 	boolean add( final T listener );
 
+	/**
+	 * Insert a listener at the specified position in this set.
+	 * The position {@code index} is clamped to the range [0..size].
+	 *
+	 * @param index
+	 *            index at which to add the specified listener
+	 * @param listener
+	 *            the listener to add
+	 * @return {@code true} if the listener was added. {@code false} if it was
+	 *         already present.
+	 */
+	boolean add( final int index, final T listener );
+
 	/**
 	 * Removes a listener from this set.
 	 *
@@ -77,6 +90,18 @@ public boolean add( final T listener )
 			return false;
 		}
 
+		@Override
+		public boolean add( final int index, final T listener )
+		{
+			if ( !list.contains( listener ) )
+			{
+				list.add( clamp( index, 0, list.size() ), listener );
+				onAdd.accept( listener );
+				return true;
+			}
+			return false;
+		}
+
 		@Override
 		public boolean remove( final T listener )
 		{
@@ -87,6 +112,11 @@ public ArrayList< T > listCopy()
 		{
 			return new ArrayList<>( list );
 		}
+
+		static int clamp( int value, int min, int max )
+		{
+			return Math.min( max, Math.max( min, value ) );
+		}
 	}
 
 	/**
@@ -111,6 +141,12 @@ public synchronized boolean add( final T listener )
 			return super.add( listener );
 		}
 
+		@Override
+		public synchronized boolean add( final int index, final T listener )
+		{
+			return super.add( index, listener );
+		}
+
 		@Override
 		public synchronized boolean remove( final T listener )
 		{