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Here are some examples where I had to use cast or notNull in my project.
Daniel asked me to make this list in order to optimize the compiler.

         cast("Errors in flow.\nFlow byte code could not be generated.\nFlow will be saved without byte code."),
flowWindow extends JInternalFrame

Can you say more about the types of the methods used? Ideally, the cases should be self-contained.

The first and third arguments should not need a cast, they are Component and String as expected. The second is supposed to be an Object in Java. Nice does not make value automatically subtypes of Object. You can use the object(...) function instead of cast(...) to do that.

For this kind of issue, I think the best is to use retyping. In particular, are you aware of the NiceSwing? project? But I would like to hear that the above fix works first. -- DanielBonniot

when I leave all casts away then the following is reported by the compiler:

   [nicec] Arguments (flow4j.designer.window.flowwindow.FlowWindow, java.lang.String, java.lang.String, do not fit: 
    [nicec] nice.lang.void showMessageDialog(?java.awt.Component, ?java.lang.Object, ?java.lang.String,
Thats why I had to use the cast -- AlexGreif

      Rectangle rect = this.getHandlesBoundsRect();
      int width = cast(rect.getWidth());
      int height = cast(rect.getHeight());
getters return double

You should use:

      Rectangle rect = this.getHandlesBoundsRect();
      int width = int(rect.getWidth());
      int height = int(rect.getHeight());

int(...) in Nice is equivalent to (int) ... in Java. See

   java.util.List<Handle> handles = new ArrayList();
      ConnectionHandle ch;
      ch = cast(handles.get(handles.size()-1));
ConnectionHandle extends Handle

How do you know that the last element has the right type? -- DanielBonniot

The draggable points of a Connection are Handles. The first and the last are connected to flowlets, thats why they are called ConnectionHandles, and the handles in between are EllbowHandles. There can be zero or more EllbowHandles?. I defined it like this. -- AlexGreif

   public class ConnectionHandle extends Handle
      implements ConnectorListener

   java.util.List<ConnectionHandle> connectionHandles = this.getHandles().filter(asConnectionHandle);
   ConnectionHandle connectionHandle = connectionHandles.get(connectionHandleIndex);
   ?java.util.List<ConnectorListener> connectorListeners = conn.getConnectorListeners();
   if (connectorListeners != null  &&  notNull(connectorListeners).contains(cast(connectionHandle))) {...}
In the last line I check the existence of a ConnectorListener in a List of ConnectorListeners. The local instance connectionHandle implements ConnectorListener.

The notNull should not be necessary, since Nice 0.7.8! :-) -- DanielBonniot

What a shame I used 0.7.7 :((
Without notNull and 0.7.8 the following error is reported

   [nicec] src/nice/flow4j/designer/figure/Connection.nice: line 211, column 80:
    [nicec] No possible call for contains.
    [nicec] Arguments: (?java.util.List<flow4j.designer.figure.ConnectorListener>, <t1691, U' | U' < nice.lang.Maybe> U'<t1691>)
    [nicec] Possibilities:
    [nicec] nice.lang.boolean contains(java.nio.charset.Charset, ?java.nio.charset.Charset)
    [nicec] nice.lang.boolean contains(flow4j.designer.figure.Handle this, Point)
    [nicec] nice.lang.boolean contains(flow4j.designer.figure.Figure this, Point)
    [nicec] nice.lang.boolean contains(flow4j.designer.figure.Connector this, Point)
    [nicec] nice.lang.boolean contains(java.awt.Component, ?java.awt.Point)
    [nicec] nice.lang.boolean contains(javax.accessibility.AccessibleRelationSet, ?java.lang.String)
    [nicec] nice.lang.boolean contains(javax.accessibility.AccessibleStateSet, ?javax.accessibility.AccessibleState)
    [nicec] nice.lang.boolean contains(javax.accessibility.AccessibleComponent, ?java.awt.Point)
    [nicec] nice.lang.boolean contains(java.awt.Polygon, ?java.awt.Point)
    [nicec] nice.lang.boolean contains(java.awt.Rectangle, ?java.awt.Rectangle)
    [nicec] nice.lang.boolean contains(java.awt.Rectangle, ?java.awt.Point)
    [nicec] nice.lang.boolean contains(java.awt.Shape, ?java.awt.geom.Point2D)
    [nicec] nice.lang.boolean contains(java.awt.Shape, ?java.awt.geom.Rectangle2D)
    [nicec] <Any K, Any V> nice.lang.boolean contains(java.util.Hashtable<K, V>, V)
    [nicec] <Any E> nice.lang.boolean contains(java.util.Collection<E>, E)
-- AlexGreif

If ConnectionHandle implements ConnectorListener?, then the cast should not be necessary either. What is the error message you get without the cast? -- DanielBonniot

you are right without cast, it compiles fine. -- AlexGreif

      ?Figure figure = getFrontFlowWindowDrawArea().getDrawing().getFigureExcept(
                  mousePos, this);
      if (figure == null)   return;
      Flowlet flowlet = cast(notNull(figure));
Flowlet extends Figure

At least the notNull should not be necessary, because you tested for null above. Does it work to remove it? -- DanielBonniot

yes it compiles. -- AlexGreif

          if (connectorListeners == null)   return;
      for (Iterator<ConnectorListener> iter = notNull(connectorListeners).iterator(); iter.hasNext();) {
         ConnectorListener ltnr =;
         if (figure.getHandles().contains(cast(ltnr))) {
            //println(" deleted: " + ltnr);

Do you really need notNull? Why? -- DanielBonniot

without I get:

    [nicec] src/nice/flow4j/designer/figure/Connector.nice: line 136, column 76:
    [nicec] Arguments (?java.util.List<flow4j.designer.figure.ConnectorListener>) do not fit: 
    [nicec] <Any T> java.util.Iterator<T> iterator(java.util.Collection<T>)

What is the type of figure.getHandles() ?

   java.util.List<Handle> getHandles() = handles;

ConnectorHandle, that extends Handle implements ConnectorListener

   getFromConnection(state) {
      java.util.List<Connection> followings = this.getFromConnections();
      for (int i = 0; i < followings.size(); i++) {
         DecisionConnection connection = cast(followings.get(i));
         if (connection.getState() == state) {
            return connection;
      return null;
DecisionConnection extends Connection

Why don't you declare that this.getFromConnections() returns a List<DecisionConnection>? -- DanielBonniot

The code above is in DecisionFlowlet, but this.getFromConnections() is declared in Flowlet that returns Connection objects.

Should I use :

      java.util.List<DecisionConnection> followings = cast(this.getFromConnections());
-- AlexGreif

more to come...

-- AlexGreif - 22 Apr 2003

OK, thanks. I'll treat them progressively.

For those that are solved, if you feel that some documentation should be added (for the numeric types, I updated the User manual, so that it compares with the Java syntax). After that they can be deleted.

Some will probably need to stay, when they are a good example of a typing problem, and how to solve it. So we can keep those there.

-- DanielBonniot - 22 Apr 2003

Topic NiceCasts . { Edit | Attach | Ref-By | Printable | Diffs | r1.24 | > | r1.23 | > | r1.22 | More }
Revision r1.6 - 23 Apr 2003 - 12:42 GMT - AlexGreif
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