java Map removal unexpected behavior
awt, collections, dictionary, java
Solution
Following-up on @RohitJain's comment, here is a simple example that reproduces the behaviour:
Map<Shape, Object> map = new HashMap<>();
java.awt.geom.Rectangle2D.Double shape = new java.awt.geom.Rectangle2D.Double(1, 1, 1, 1);
map.put(shape, null);
System.out.println(map.size()); //1
shape.setRect(2, 2, 2, 2); //mutate
System.out.println(map.size()); //still 1
map.keySet().remove(shape);
System.out.println(map.size()); //still 1
The underlying problem is that the Shape is mutated while in the map.
Problem
code: ``` public class FeatureBuilder implements IFeatureBuilder { private final Map< java.awt.Shape, ShapeAttributes > shapes = new HashMap<>(); [...] @Override public void addToContainer( java.awt.Shape shape ) { System.err.println( shape.getClass()); shapes.put( shape, new ShapeAttributes( ... )); } @Override public void removeFromContainer( double x, double y ) { final Set< Shape > rm = new HashSet<>(); final Point2D loc = new Point2D.Double( x, y ); for( final Shape shape : shapes.keySet()) { if( shape.contains( loc )) { System.err.println( "shapes.containsKey( shape ): " + shapes.containsKey( shape )); rm.add( shape ); } } System.err.println( "cardinality before removal : " + shapes.size()); shapes.keySet().removeAll( rm ); System.err.println( "cardinality after removal : " + shapes.size()); } ``` output: ``` class java.awt.geom.Rectangle2D$Double shapes.containsKey( shape ): false <<<<<<< This is unexpected! cardinality before removal : 1 rm cardinality : 1 cardinality after removal : 1 ``` I'm surprised: an instance retrieved by a `for` iterator on `Map.keySet()` is not a key in the `Map`! How is this possible? The main bug in this method is the selected instances of Shape placed in `rm` are not removed from `shapes`. After reading your answers the code becomes: ``` public class DecoratedShape { public final Shape _shape; public /* */ Color _stroke = Color.BLACK; public /* */ float _strokeWidth = 3.0f; public /* */ Color _fill = Color.BLACK; public DecoratedShape( Shape shape, Color stroke, float strokeWidth, Color fill ) { _shape = shape; _stroke = stroke; _strokeWidth = strokeWidth; _fill = fill; } public boolean contains( Point2D loc ) { return _shape.contains( loc ); } public void paint( Graphics2D g ) { g.setStroke( new BasicStroke( _strokeWidth )); g.setColor( _fill ); g.fill( _shape ); g.setColor( _stroke ); g.draw( _shape ); } } public class FeatureBuilder implements IFeatureBuilder { private final List< DecoratedShape > _shapes = new LinkedList<>(); [...] @Override public void addToContainer( Object o ) { _shapes.add( new DecoratedShape((Shape)o, _stroke, _strokeWidth, _fill )); } @Override public void removeFromContainer( double x, double y ) { final Set<DecoratedShape> rm = new HashSet<>(); final Point2D loc = new Point2D.Double( x, y ); for( final DecoratedShape shape : _shapes ){ if( shape.contains( loc ) ){ rm.add( shape ); } } _shapes.removeAll( rm ); } public void paint( Graphics2D g ) { for( final DecoratedShape shape : _shapes ) { shape.paint( g ); } } } ``` And now, it works as expected... Thanks a lot!