Code cleaned up.

Author: RuedigerLunde

aima-core/src/main/java/aima/core/search/framework/qsearch/BidirectionalSearch.java

@@ -44,7 +44,7 @@ public class BidirectionalSearch<S, A> extends QueueSearch<S, A> {
 	private boolean isReverseActionTestEnabled = true;
 
 	// index 0: original problem, index 1: reverse problem
-	private List<Map<S, ExtendedNode<S, A>>> explored;
+	private final List<Map<S, ExtendedNode<S, A>>> explored;
 	private ExtendedNode<S, A> goalStateNode;
 
 	public BidirectionalSearch() {
@@ -78,7 +78,6 @@ public BidirectionalSearch(NodeFactory<S, A> nodeFactory) {
 	 *         containing a single NoOp Action if already at the goal, or an
 	 *         empty list if the goal could not be found.
 	 */
-	@SuppressWarnings("unchecked")
 	public Optional<Node<S, A>> findNode(Problem<S, A> problem, Queue<Node<S, A>> frontier) {
 		assert (problem instanceof BidirectionalProblem);
 
@@ -103,7 +102,7 @@ public Optional<Node<S, A>> findNode(Problem<S, A> problem, Queue<Node<S, A>> fr
 
 		while (!isFrontierEmpty() && !Tasks.currIsCancelled()) {
 			// choose a leaf node and remove it from the frontier
-			ExtendedNode<S, A> node = (ExtendedNode) removeFromFrontier();
+			ExtendedNode<S, A> node = (ExtendedNode<S, A>) removeFromFrontier();
 			ExtendedNode<S, A> nodeFromOtherProblem;
 
 			// if the node contains a goal state then return the corresponding solution
@@ -156,8 +155,7 @@ protected void addToFrontier(Node<S, A> node) {
 	 * @return A node of a not yet explored state.
 	 */
 	protected Node<S, A> removeFromFrontier() {
-		cleanUpFrontier(); // not really necessary because isFrontierEmpty
-							// should be called before...
+		cleanUpFrontier(); // not really necessary because isFrontierEmpty should be called before...
 		Node<S, A> result = frontier.remove();
 		updateMetrics(frontier.size());
 		// add the node to the explored set of the corresponding problem
@@ -180,7 +178,7 @@ protected boolean isFrontierEmpty() {
 	 * head of the frontier.
 	 */
 	private void cleanUpFrontier() {
-		while (!frontier.isEmpty() && isExplored(frontier.element()))
+		while (!frontier.isEmpty() && isExplored(frontier.peek()))
 			frontier.remove();
 	}
 
@@ -215,8 +213,7 @@ private Optional<Node<S, A>> getSolution(Problem<S, A> orgP, ExtendedNode<S, A>
 
 	/**
 	 * Returns the action which leads from the state of <code>node</code> to the
-	 * state of the node's parent, if such an action exists in problem
-	 * <code>orgP</code>.
+	 * state of the node's parent, if such an action exists in problem <code>orgP</code>.
 	 */
 	private A getReverseAction(Problem<S, A> orgP, Node<S, A> node) {
 		S currState = node.getState();
@@ -230,15 +227,13 @@ private A getReverseAction(Problem<S, A> orgP, Node<S, A> node) {
 		return null;
 	}
 
-	@SuppressWarnings("unchecked")
 	private boolean isExplored(Node<S, A> node) {
-		ExtendedNode<S, A> eNode =  (ExtendedNode) node;
+		ExtendedNode<S, A> eNode = (ExtendedNode<S, A>) node;
 		return explored.get(eNode.getProblemIndex()).containsKey(eNode.getState());
 	}
 
-	@SuppressWarnings("unchecked")
 	private void setExplored(Node<S, A> node) {
-		ExtendedNode<S, A> eNode = (ExtendedNode) node;
+		ExtendedNode<S, A> eNode = (ExtendedNode<S, A>) node;
 		explored.get(eNode.getProblemIndex()).put(eNode.getState(), eNode);
 	}
 

aima-core/src/main/java/aima/core/search/framework/qsearch/GraphSearch4e.java

@@ -141,7 +141,7 @@ private Node<S, A> removeFromFrontier() {
 	 * on all paths. It is assumed that the frontier contains at least one node.
 	 */
 	protected boolean canPossiblyBeImproved(Node<S, A> solution) {
-		return isCheaper(frontier.element(), solution);
+		return isCheaper(frontier.peek(), solution);
 	}
 
 	/**

aima-core/src/main/java/aima/core/search/framework/qsearch/GraphSearchBFS.java

@@ -43,8 +43,8 @@
  */
 public class GraphSearchBFS<S, A> extends TreeSearch<S, A> {
 
-	private Set<S> explored = new HashSet<>();
-	private Set<S> frontierStates = new HashSet<>();
+	private final Set<S> explored = new HashSet<>();
+	private final Set<S> frontierStates = new HashSet<>();
 
 	public GraphSearchBFS() {
 		this(new NodeFactory<>());

aima-core/src/main/java/aima/core/search/framework/qsearch/QueueSearch.java

@@ -92,7 +92,8 @@ protected void updateMetrics(int queueSize) {
 	}
 
 	protected Optional<Node<S, A>> asOptional(Node<S, A> node) {
-		metrics.set(METRIC_PATH_COST, node.getPathCost());
-		return Optional.of(node);
+		if (node != null)
+			metrics.set(METRIC_PATH_COST, node.getPathCost());
+		return Optional.ofNullable(node);
 	}
 }

aima-core/src/main/java/aima/core/search/uninformed/DepthLimitedSearch.java

@@ -89,10 +89,9 @@ public Optional<S> findState(Problem<S, A> p) {
 
 	public Optional<Node<S, A>> findNode(Problem<S, A> p) {
 		clearMetrics();
-		// return RECURSIVE-DLS(MAKE-NODE(INITIAL-STATE[problem]), problem,
-		// limit)
+		// return RECURSIVE-DLS(MAKE-NODE(INITIAL-STATE[problem]), problem, limit)
 		Node<S, A> node = recursiveDLS(nodeFactory.createNode(p.getInitialState()), p, limit);
-		return node != null ? Optional.of(node) : Optional.empty();
+		return Optional.ofNullable(node);
 	}
 
 	// function RECURSIVE-DLS(node, problem, limit) returns a solution, or