source: josm/src/org/openstreetmap/josm/data/DataSetChecker.java@ 290

package org.openstreetmap.josm.data;

import java.util.HashSet;
import java.util.Set;

import javax.swing.JOptionPane;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.osm.OsmPrimitive;
import org.openstreetmap.josm.gui.layer.Layer;
import org.openstreetmap.josm.gui.layer.OsmDataLayer;

public class DataSetChecker {

        public static void check() {
                if (Main.map == null)
                        return;

                Set<OsmPrimitive> s = new HashSet<OsmPrimitive>();
                for (Layer l : Main.map.mapView.getAllLayers()) {
                        if (l instanceof OsmDataLayer) {
                                for (OsmPrimitive osm : ((OsmDataLayer)l).data.allPrimitives()) {
                                        if (s.contains(osm)) {
                                JOptionPane.showMessageDialog(Main.parent, "cross references");
                                return;
                                        }
                                        s.add(osm);
                                }
                        }
                }
                
                if (Main.map.mapView.getActiveLayer() instanceof OsmDataLayer) {
                        OsmDataLayer l = (OsmDataLayer)Main.map.mapView.getActiveLayer();
                        if (l.data != Main.ds) {
                                JOptionPane.showMessageDialog(Main.parent, "Main.ds / active layer mismatch");
                                return;
                        }
                }

                JOptionPane.showMessageDialog(Main.parent, "working");
        }
}