incremental: improve error messages

Author: mtf90

incremental/src/main/java/net/automatalib/incremental/ConflictException.java

@@ -20,15 +20,6 @@
  */
 public class ConflictException extends IllegalArgumentException {
 
-    /**
-     * Creates an exception with no specific error message.
-     *
-     * @see IllegalArgumentException#IllegalArgumentException()
-     */
-    public ConflictException() {
-        // default constructor
-    }
-
     /**
      * Creates an exception with a given error message.
      *

incremental/src/main/java/net/automatalib/incremental/mealy/tree/DynamicIncrementalMealyTreeBuilder.java

@@ -65,7 +65,9 @@ public void insert(Word<? extends I> input, Word<? extends O> outputWord) {
                 curr = insertNode(curr, sym, out);
             } else {
                 if (!Objects.equals(out, edge.getOutput())) {
-                    throw new ConflictException();
+                    throw new ConflictException(
+                            "Error inserting " + input.prefix(i + 1) + " / " + outputWord.prefix(i + 1) +
+                            ": Incompatible output symbols: " + out + " vs " + edge.getOutput());
                 }
                 curr = edge.getTarget();
             }

incremental/src/main/java/net/automatalib/incremental/mealy/tree/IncrementalMealyTreeBuilder.java

@@ -49,7 +49,9 @@ public void insert(Word<? extends I> input, Word<? extends O> outputWord) {
                 curr = insertNode(curr, sym, out);
             } else {
                 if (!Objects.equals(out, edge.getOutput())) {
-                    throw new ConflictException();
+                    throw new ConflictException(
+                            "Error inserting " + input.prefix(i + 1) + " / " + outputWord.prefix(i + 1) +
+                            ": Incompatible output symbols: " + out + " vs " + edge.getOutput());
                 }
                 curr = edge.getTarget();
             }

incremental/src/main/java/net/automatalib/incremental/moore/tree/IncrementalMooreTreeBuilder.java

@@ -190,11 +190,12 @@ public void insert(Word<? extends I> word, Word<? extends O> output) {
         for (I sym : word) {
             int inputIdx = alphabet.getSymbolIndex(sym);
             Node<O> succ = curr.getChild(inputIdx);
+            O out = outIter.next();
             if (succ == null) {
-                succ = new Node<>(outIter.next());
+                succ = new Node<>(out);
                 curr.setChild(inputIdx, alphabetSize, succ);
-            } else if (!Objects.equals(succ.getOutput(), outIter.next())) {
-                throw new ConflictException();
+            } else if (!Objects.equals(succ.getOutput(), out)) {
+                throw new ConflictException("Incompatible outputs: " + succ.getOutput() + " vs " + out);
             }
             curr = succ;
         }