Implement a non-naive toString for DirectedEdge to avoid recursive calls

src/de/tudarmstadt/maki/simonstrator/api/common/graph/DirectedEdge.java

@@ -23,6 +23,7 @@ package de.tudarmstadt.maki.simonstrator.api.common.graph;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Map.Entry;
 
 import de.tudarmstadt.maki.simonstrator.api.Graphs;
 import de.tudarmstadt.maki.simonstrator.api.component.sis.type.SiSType;
@@ -185,10 +186,23 @@ public class DirectedEdge implements IEdge {
 	public String toString() {
 		return "DirectedEdge [" + (startNode != null ? startNode + " -> " : "")
 				+ (endNode != null ? endNode : "")
-				+ (properties != null ? ", properties=" + properties : "")
+				+ (properties != null ? ", properties=" + formatProperties() : "")
 				+ "]";
 	}
 
+	public String formatProperties() {
+		final StringBuilder builder = new StringBuilder();
+		for (final Entry<SiSType<?>, Object> entry : this.properties.entrySet()) {
+			if (entry.getKey().getType().isInstance(IEdge.class))
+			{
+				builder.append(String.format("%s, %s", entry.getKey().toString(), ((IEdge) entry.getValue()).getId()));
+			} else {
+				builder.append(String.format("%s, %s", entry.getKey().toString(), entry.getValue().toString()));
+			}
+		}
+		return builder.toString();
+	}
+
 	@Override
 	public int hashCode() {
 		final int prime = 31;