Refactoring

- changed to maven
- modified hashMap and HashSet to Tree
- modified files path

.gitignore

@@ -125,6 +125,7 @@ local.properties
 
 
 # mine
+target/
 .idea/*
 .project
 *.iml

build.gradle

@@ -1,32 +0,0 @@
-apply plugin: 'java'
-apply plugin: 'eclipse'
-
-version='1.0-SNAPSHOT'
-
-jar {
-    manifest {
-        attributes 'Main-Class': 'berack96.lib.graph.view.Main'
-    }
-    from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
-}
-
-test {
-    useJUnitPlatform()
-}
-
-sourceSets.main.java {
-    srcDirs "src"
-    srcDirs "test"
-}
-
-repositories {
-    mavenCentral()
-}
-
-dependencies {
-    implementation 'org.junit.jupiter:junit-jupiter:5.5.2'
-    compile group: 'com.google.code.gson', name: 'gson', version: '2.8.5'
-	
-	/*compile group: 'commons-collections', name: 'commons-collections', version: '3.2'*/
-	testCompile 'junit:junit:5.5.2'
-}

pom.xml

@@ -0,0 +1,80 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>berack96</groupId>
+    <artifactId>Graph</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>5.9.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <version>5.9.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.9.1</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>2.2</version>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <version>2.2</version>
+                <configuration>
+                  <descriptorRefs>
+                    <descriptorRef>jar-with-dependencies</descriptorRef>
+                  </descriptorRefs>
+                  <archive>
+                    <manifest>
+                      <mainClass>berack96.lib.graph.view.Main</mainClass>
+                    </manifest>
+                  </archive>
+                </configuration>
+                <executions>
+                  <execution>
+                    <phase>package</phase>
+                    <goals>
+                      <goal>single</goal>
+                    </goals>
+                  </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>attach-javadocs</id>
+                        <phase>prepare-package</phase>
+                        <goals>
+                            <goal>jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+    <properties>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+    </properties>
+
+</project>

src/main/java/berack96/lib/graph/Graph.java

@@ -18,18 +18,46 @@ import java.util.function.Consumer;
  */
 public abstract class Graph<V> implements Iterable<V> {
 
+    //------------------- STAIC -----------------
+
     public static final int NO_EDGE = 0;
     public final static String NOT_CONNECTED = "The source vertex doesn't have a path that reach the destination";
     public final static String PARAM_NULL = "The parameter must not be null";
     public final static String VERTEX_NOT_CONTAINED = "The vertex must be contained in the graph";
 
     /**
-     * Map that contains the vertex as key and a set of all the marker associated with it.
+     * Create the default map. All operations are O(log(n))<br>
+     * It returns a TreeMap with a ObjectComparator as comparator.<br>
+     * This way all the graphs will use the same maps.<br>
+     * It is not required to use this method, but it is highly recommended.<br>
+     * 
+     * @return A newly created TreeMap instance with ObjectsComparator as comparator
      */
-    private final Map<V, Set<Object>> markers = new HashMap<>();
+    public final static <X, Y> Map<X, Y> getDefaultMap() {
+        return new TreeMap<X, Y>(ObjectsComparator.instance);
+    }
 
     /**
-     * Get a new instance of this Graph.
+     * Create the default set. All operations are O(log(n))<br>
+     * It returns a TreeSet with a ObjectComparator as comparator.<br>
+     * This way all the graphs will use the same sets.<br>
+     * It is not required to use this method, but it is highly recommended.<br>
+     * 
+     * @return A newly created TreeSet instance with ObjectsComparator as comparator
+     */
+    public final static <X> Set<X> getDefaultSet() {
+        return new TreeSet<X>(ObjectsComparator.instance);
+    }
+
+    //------------------- INSTANCE -----------------
+
+    /**
+     * Map that contains the vertex as key and a set of all the marker associated with it.
+     */
+    private final Map<V, Set<Object>> markers = getDefaultMap();
+
+    /**
+     * Get a new instance of this graph.
      *
      * @return A new instance of the graph
      */
@@ -90,7 +118,7 @@ public abstract class Graph<V> implements Iterable<V> {
      * @param vertices a collection of the vertices to add
      * @throws NullPointerException if the set is null
      */
-    public void addAll(@SuppressWarnings("ConstantConditions") Collection<V> vertices) throws NullPointerException {
+    public void addAll(Collection<V> vertices) throws NullPointerException {
         check(vertices);
         for (V vertex : vertices)
             addIfAbsent(vertex);
@@ -283,7 +311,7 @@ public abstract class Graph<V> implements Iterable<V> {
      * After this method's call the graph will have only vertices, and no edge.
      */
     public void removeAllEdge() {
-        Collection<V> vertices = vertices();
+        Set<V> vertices = vertices();
         removeAll();
         addAll(vertices);
     }
@@ -292,11 +320,11 @@ public abstract class Graph<V> implements Iterable<V> {
      * Retrieve all the edges of a particular vertex.<br>
      *
      * @param vertex a vertex of the graph
-     * @return a collection of edges
+     * @return a set of edges
      * @throws NullPointerException     if the vertex is null
      * @throws IllegalArgumentException if the vertex is not contained in the graph
      */
-    public abstract Collection<Edge<V>> edgesOf(V vertex) throws NullPointerException, IllegalArgumentException;
+    public abstract Set<Edge<V>> edgesOf(V vertex) throws NullPointerException, IllegalArgumentException;
 
     /**
      * Get all the vertices that are children of the vertex passed as parameter.<br>
@@ -304,33 +332,33 @@ public abstract class Graph<V> implements Iterable<V> {
      * where V1 is the source of that edge.
      *
      * @param vertex the source vertex
-     * @return an array of vertices
+     * @return a set of vertices
      * @throws NullPointerException     if the vertex is null
      * @throws IllegalArgumentException if the vertex is not contained in the graph
      */
-    public abstract Collection<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException;
+    public abstract Set<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException;
 
     /**
      * Get all the vertices that have the vertex passed as their child.<br>
      * Basically is the opposite of {@link #getChildren(Object)}
      *
      * @param vertex a vertex of the graph
-     * @return an array of ancestors of the vertex
+     * @return a set of ancestors of the vertex
      * @throws NullPointerException     if one of the parameters is null
      * @throws IllegalArgumentException if one of the vertex is not contained in the graph
      */
-    public abstract Collection<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException;
+    public abstract Set<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException;
 
     /**
      * Get all the marks of this graph.<br>
-     * Specifically it will return a collection of marks where every mark<br>
+     * Specifically it will return a Set of marks where every mark<br>
      * as associated at least one vertex of the graph.<br>
-     * If the graph doesn't have vertex marked then it is returned an empty collection.
+     * If the graph doesn't have vertex marked then it is returned an empty Set.
      *
-     * @return a collection of marks
+     * @return a set of marks
      */
-    public final Collection<Object> marks() {
+    public final Set<Object> marks() {
-        Collection<Object> ret = new HashSet<>();
+        Set<Object> ret = getDefaultSet();
         markers.forEach((v, set) -> ret.addAll(set));
         return ret;
     }
@@ -348,7 +376,7 @@ public abstract class Graph<V> implements Iterable<V> {
     public final void mark(V vertex, Object mark) throws NullPointerException, IllegalArgumentException {
         check(mark);
         checkVert(vertex);
-        Set<Object> marks = markers.computeIfAbsent(vertex, v -> new HashSet<>());
+        Set<Object> marks = markers.computeIfAbsent(vertex, v -> getDefaultSet());
         marks.add(mark);
     }
 
@@ -392,12 +420,12 @@ public abstract class Graph<V> implements Iterable<V> {
      * If there aren't vertices with that mark then it is returned an empty set.<br>
      *
      * @param mark the mark
-     * @return all the vertices that are marked with that specific mark
+     * @return a set of all the vertices that are marked with that specific mark
      * @throws NullPointerException if the mark is null
      */
-    public final Collection<V> getMarkedWith(Object mark) throws NullPointerException {
+    public final Set<V> getMarkedWith(Object mark) throws NullPointerException {
         check(mark);
-        Collection<V> vertices = new ArrayList<>(markers.size());
+        Set<V> vertices = getDefaultSet();
         markers.forEach((v, set) -> {
             if (set.contains(mark))
                 vertices.add(v);
@@ -408,16 +436,16 @@ public abstract class Graph<V> implements Iterable<V> {
     /**
      * Get all the marker of this vertex.<br>
      * If the vertex doesn't have any mark, then it will return an empty set.<br>
-     * Note: modifying the returned collection affect the marker of the vertex.
+     * Note: modifying the returned Set affect the marker of the vertex.
      *
      * @param vertex the vertex
-     * @return all the mark to the vertex or an empty collection if none
+     * @return a set of all the mark to the vertex or an empty Set if none
      * @throws NullPointerException     if the vertex is null
      * @throws IllegalArgumentException if the vertex is not contained in the graph
      */
-    public final Collection<Object> getMarks(V vertex) throws NullPointerException, IllegalArgumentException {
+    public final Set<Object> getMarks(V vertex) throws NullPointerException, IllegalArgumentException {
         checkVert(vertex);
-        return markers.getOrDefault(vertex, new HashSet<>());
+        return markers.getOrDefault(vertex, getDefaultSet());
     }
 
     /**
@@ -428,7 +456,7 @@ public abstract class Graph<V> implements Iterable<V> {
      */
     public final void unMarkAll(Object mark) throws NullPointerException {
         check(mark);
-        Collection<V> toRemove = new ArrayList<>(markers.size());
+        Set<V> toRemove = getDefaultSet();
         markers.forEach((v, set) -> {
             set.remove(mark);
             if (set.size() == 0)
@@ -448,23 +476,23 @@ public abstract class Graph<V> implements Iterable<V> {
 
     /**
      * Get all the vertices in the graph.<br>
-     * If the graph doesn't contains vertices, it'll return an empty collection.<br>
+     * If the graph doesn't contains vertices, it'll return an empty Set.<br>
      *
-     * @return an array that include all the vertices
+     * @return a set that include all the vertices
      */
-    public Collection<V> vertices() {
+    public Set<V> vertices() {
-        Collection<V> collection = new ArrayList<>();
+        Set<V> vertices = getDefaultSet();
-        forEach(collection::add);
+        forEach(vertices::add);
-        return collection;
+        return vertices;
     }
 
     /**
      * Get all the edges in the graph.<br>
-     * If the graph doesn't contains edges, it'll return an empty collection.<br>
+     * If the graph doesn't contains edges, it'll return an empty Set.<br>
      *
-     * @return a collection that include all the edges
+     * @return a Set that include all the edges
      */
-    public abstract Collection<Edge<V>> edges();
+    public abstract Set<Edge<V>> edges();
 
     /**
      * Tells the degree of a vertex.<br>
@@ -523,40 +551,44 @@ public abstract class Graph<V> implements Iterable<V> {
     public final Graph<V> subGraph(V source, int depth) throws NullPointerException, IllegalArgumentException {
         checkVert(source);
         Graph<V> sub = getNewInstance();
-        Set<V> vertices = new HashSet<>(this.size() + 1, 1);
+        Set<V> vertices = getDefaultSet();
         new BFS<V>().setMaxDepth(Math.max(depth, 0)).visit(this, source, vertices::add);
 
         sub.addAll(vertices);
         for (V src : vertices)
             for (V dest : getChildren(src))
                 if (sub.contains(dest))
-                    sub.addEdge(new Edge<>(src, dest, this.getWeight(src, dest)));
+                    sub.addEdge(src, dest, this.getWeight(src, dest));
         return sub;
     }
 
     /**
-     * Get a sub-graph of the current one with only the vertex marked with the selected markers.<br>
+     * Get a sub-graph of the current one with only the vertex marked with the selected markers. (OR set operation)<br>
      * Each vertex will have all his markers and his edges, but only the ones with the destination marked with the same marker.<br>
      * If the marker is not specified or is null then the returning graph will have all the vertices that are not marked by any marker.<br>
-     * If the graph doesn't contain any vertex with that marker then an empty graph is returned.
+     * If in the list of markers there is a null marker it will be skipped.<br>
+     * If the graph doesn't contain any vertex with any marker passed then an empty graph is returned.
      *
      * @param marker one or more markers
      * @return a sub-graph of the current graph
      */
     public final Graph<V> subGraph(Object... marker) {
         final Graph<V> sub = getNewInstance();
-        final Set<V> allVertices = new HashSet<>();
+        final Set<V> allVertices = getDefaultSet();
-        final Set<Object> allMarkers = new HashSet<>();
+        final Set<Object> allMarkers = getDefaultSet();
-        final boolean isEmpty = (marker == null || marker.length == 0);
         
-        if (!isEmpty) {
+        if (marker != null && marker.length > 0)
-            Collections.addAll(allMarkers, marker);
+            for(int i=0; i<marker.length; i++)
+                if(marker[i] != null)
+                    allMarkers.add(marker[i]);
+        
+        if(allMarkers.size() > 0)
             markers.forEach((v, set) -> {
                 if (!Collections.disjoint(allMarkers, set))
                     allVertices.add(v);
             });
-        } else {
+        else {
-            Collection<V> toAdd = vertices();
+            Set<V> toAdd = vertices();
             toAdd.removeAll(markers.keySet());
             allVertices.addAll(toAdd);
         }
@@ -606,7 +638,6 @@ public abstract class Graph<V> implements Iterable<V> {
         return dijkstra.getLastDistance();
     }
 
-
     /**
      * Check if the object passed is not null.
      * If it's null then throws eventual exception

src/main/java/berack96/lib/graph/GraphDirected.java

@@ -4,10 +4,8 @@ import berack96.lib.graph.visit.VisitSCC;
 import berack96.lib.graph.visit.VisitTopological;
 import berack96.lib.graph.visit.impl.Tarjan;
 
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 /**
  * This is a more specific interface for an implementation of a Undirected Graph.<br>
@@ -70,17 +68,17 @@ public abstract class GraphDirected<V> extends Graph<V> {
     /**
      * Retrieve all the edges of a particular vertex.<br>
      * Note: the edges that are returned are the one that have this vertex as destination and another as source.<br>
-     * Note2: depending on the implementation, modifying the returned collection<br>
+     * Note2: depending on the implementation, modifying the returned Set<br>
      * could affect the graph behavior and the changes could be reflected to the graph.
      *
      * @param vertex a vertex of the graph
-     * @return a collection of edges
+     * @return a Set of edges
      * @throws NullPointerException     if the vertex is null
      * @throws IllegalArgumentException if the vertex is not contained in the graph
      */
-    public Collection<Edge<V>> getEdgesIn(V vertex) throws NullPointerException, IllegalArgumentException {
+    public Set<Edge<V>> getEdgesIn(V vertex) throws NullPointerException, IllegalArgumentException {
-        Collection<V> ancestors = getAncestors(vertex);
+        Set<V> ancestors = getAncestors(vertex);
-        Collection<Edge<V>> edgesIn = new HashSet<>(ancestors.size());
+        Set<Edge<V>> edgesIn = getDefaultSet();
 
         for (V ancestor : ancestors) {
             int weight = getWeight(ancestor, vertex);
@@ -93,17 +91,17 @@ public abstract class GraphDirected<V> extends Graph<V> {
     /**
      * Retrieve all the edges that goes OUT of a particular vertex.<br>
      * Note: the edges that are returned are the one that have this vertex as source and another one as destination.<br>
-     * Note2: depending on the implementation, modifying the returned collection<br>
+     * Note2: depending on the implementation, modifying the returned Set<br>
      * could affect the graph behavior and the changes could be reflected to the graph.
      *
      * @param vertex a vertex of the graph
-     * @return a collection of edges
+     * @return a Set of edges
      * @throws NullPointerException     if the vertex is null
      * @throws IllegalArgumentException if the vertex is not contained in the graph
      */
-    public Collection<Edge<V>> getEdgesOut(V vertex) throws NullPointerException, IllegalArgumentException {
+    public Set<Edge<V>> getEdgesOut(V vertex) throws NullPointerException, IllegalArgumentException {
-        Collection<V> children = getChildren(vertex);
+        Set<V> children = getChildren(vertex);
-        Collection<Edge<V>> edgesOut = new HashSet<>(children.size());
+        Set<Edge<V>> edgesOut = getDefaultSet();
 
         for (V child : children) {
             int weight = getWeight(vertex, child);
@@ -178,26 +176,26 @@ public abstract class GraphDirected<V> extends Graph<V> {
      * The strongly connected components or disconnected components of an arbitrary directed graph
      * form a partition into subgraphs that are themselves strongly connected.
      *
-     * @return a collection containing the strongly connected components
+     * @return a Set containing the strongly connected components
      */
-    public final Collection<Collection<V>> stronglyConnectedComponents() {
+    public final Set<Set<V>> stronglyConnectedComponents() {
         VisitSCC<V> visit = new Tarjan<>();
         visit.visit(this, null, null);
         return visit.getSCC();
     }
 
     @Override
-    public Collection<Edge<V>> edgesOf(V vertex) throws NullPointerException, IllegalArgumentException {
+    public Set<Edge<V>> edgesOf(V vertex) throws NullPointerException, IllegalArgumentException {
-        Collection<Edge<V>> edges = getEdgesIn(vertex);
+        Set<Edge<V>> edges = getEdgesIn(vertex);
         edges.addAll(getEdgesOut(vertex));
         return edges;
     }
 
     @Override
-    public Collection<Edge<V>> edges() {
+    public Set<Edge<V>> edges() {
-        Collection<Edge<V>> collection = new ArrayList<>();
+        Set<Edge<V>> set = getDefaultSet();
-        forEach(v -> collection.addAll(getEdgesIn(v)));
+        forEach(v -> set.addAll(getEdgesIn(v)));
-        return collection;
+        return set;
     }
 
     @Override

src/main/java/berack96/lib/graph/GraphUndirected.java

@@ -3,8 +3,7 @@ package berack96.lib.graph;
 import berack96.lib.graph.visit.VisitMST;
 import berack96.lib.graph.visit.impl.Prim;
 
-import java.util.Collection;
+import java.util.Set;
-import java.util.LinkedList;
 
 /**
  * This is a more specific interface for an implementation of a Directed Graph.<br>
@@ -19,27 +18,27 @@ public abstract class GraphUndirected<V> extends Graph<V> {
     /**
      * The connected components of an arbitrary undirected graph form a partition into subgraphs that are themselves connected.
      *
-     * @return a collection containing the strongly connected components
+     * @return a Set containing the strongly connected components
      */
-    public Collection<Collection<V>> connectedComponents() {
+    public Set<Set<V>> connectedComponents() {
         return null;
     }
 
     /**
      * minimum spanning forest or minimum spamming tree of the graph
      *
-     * @return A collection of edges representing the M.S.F.
+     * @return A Set of edges representing the M.S.F.
      */
-    public Collection<Edge<V>> minimumSpanningForest() {
+    public Set<Edge<V>> minimumSpanningForest() {
         VisitMST<V> visit = new Prim<>();
         visit.visit(this, iterator().next(), null);
         return visit.getMST();
     }
 
     @Override
-    public Collection<Edge<V>> edgesOf(V vertex) throws NullPointerException, IllegalArgumentException {
+    public Set<Edge<V>> edgesOf(V vertex) throws NullPointerException, IllegalArgumentException {
         checkVert(vertex);
-        Collection<Edge<V>> edges = new LinkedList<>();
+        Set<Edge<V>> edges = getDefaultSet();
         getChildren(vertex).forEach(v -> edges.add(new Edge<>(vertex, v, getWeight(vertex, v))));
         return edges;
     }

src/main/java/berack96/lib/graph/ObjectsComparator.java

@@ -0,0 +1,18 @@
+package berack96.lib.graph;
+import java.util.Comparator;
+
+/**
+ * Compare two arbitrary objects.<br>
+ * It uses the method hashCode that every object has to compare two objects.<br>
+ * This is a simple use 
+ */
+public class ObjectsComparator implements Comparator<Object> {
+    static public final ObjectsComparator instance = new ObjectsComparator();
+    
+    private ObjectsComparator(){};
+
+    @Override
+    public int compare(Object o1, Object o2) {
+        return o1.hashCode() - o2.hashCode();
+    }
+}

src/main/java/berack96/lib/graph/impl/ListGraph.java

@@ -14,7 +14,8 @@ import java.util.concurrent.atomic.AtomicInteger;
  */
 public class ListGraph<V> extends GraphDirected<V> {
 
-	final private Map<V, List<Adj>> adj = new Hashtable<>();
+	// in case of thread safety use -> Collections.synchronizedSortedMap(TreeMap)
+	final private Map<V, List<Adj>> adj = getDefaultMap();
 
 	@Override
 	public Iterator<V> iterator() {
@@ -73,18 +74,18 @@ public class ListGraph<V> extends GraphDirected<V> {
 	}
 
 	@Override
-	public Collection<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
+	public Set<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
 		checkVert(vertex);
-		Collection<V> children = new HashSet<>();
+		Set<V> children = getDefaultSet();
 		for (Adj adj : adj.get(vertex))
 			children.add(adj.vertex);
 		return children;
 	}
 
 	@Override
-	public Collection<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
+	public Set<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
 		checkVert(vertex);
-		Collection<V> ancestors = new HashSet<>();
+		Set<V> ancestors = getDefaultSet();
 		adj.forEach((v, list) -> {
 			if (getAdj(list, vertex) != null)
 				ancestors.add(v);

src/main/java/berack96/lib/graph/impl/MapGraph.java

@@ -7,11 +7,12 @@ import java.util.*;
 import java.util.concurrent.atomic.AtomicInteger;
 
 /**
- * Graph that uses HashMap for vertices and edges<br>
+ * Graph that uses TreeMap for vertices and edges<br>
  * More specifically it utilizes a Map containing all the vertices mapped to all their edges<br>
  * Technically this version of the graph combine the fast adding/removing of the edges of the Matrix implementation,
  * with the low memory and fast adding/removing of vertices of the Linked List implementation.<br>
- * This happen if the HashMap is not reallocated. So in the end each operation of adding or removing has O(n)
+ * "Fast" in this case means O(log(n)) since it is a tree, so not tecnically as fast as O(1),
+ * but better than O(n).<br>
  *
  * @param <V> the vertices
  * @author Berack96
@@ -23,7 +24,7 @@ public class MapGraph<V> extends GraphDirected<V> {
 	 * The first vertex is the vertex where start the edge, the second one is where the edge goes<br>
 	 * If an edge exist, then it's weight is returned
 	 */
-	private final Map<V, Map<V, Integer>> edges = new HashMap<>();
+	private final Map<V, Map<V, Integer>> edges = getDefaultMap();
 
 	@Override
 	public Iterator<V> iterator() {
@@ -39,7 +40,7 @@ public class MapGraph<V> extends GraphDirected<V> {
 	@Override
 	public void add(V vertex) {
 		check(vertex);
-		edges.computeIfAbsent(vertex, v -> new HashMap<>());
+		edges.computeIfAbsent(vertex, v -> new TreeMap<>());
 		edges.forEach((v, adj) -> adj.remove(vertex));
 		edges.get(vertex).clear();
 	}
@@ -79,15 +80,15 @@ public class MapGraph<V> extends GraphDirected<V> {
 	}
 
 	@Override
-	public Collection<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
+	public Set<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
 		checkVert(vertex);
 		return new HashSet<>(edges.get(vertex).keySet());
 	}
 
 	@Override
-	public Collection<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
+	public Set<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
 		checkVert(vertex);
-		Collection<V> ancestors = new HashSet<>();
+		Set<V> ancestors = getDefaultSet();
 		edges.forEach((v, adj) -> {
 			if (adj.containsKey(vertex))
 				ancestors.add(v);

src/main/java/berack96/lib/graph/impl/MatrixGraph.java

@@ -13,7 +13,7 @@ import java.util.*;
  */
 public class MatrixGraph<V> extends GraphDirected<V> {
 
-	private final Map<V, Integer> map = new HashMap<>();
+	private final Map<V, Integer> map = getDefaultMap();
 	private int[][] matrix = new int[0][0];
 
 	@Override
@@ -80,10 +80,10 @@ public class MatrixGraph<V> extends GraphDirected<V> {
 	}
 
 	@Override
-	public Collection<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
+	public Set<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
 		checkVert(vertex);
 		int x = map.get(vertex);
-		Collection<V> children = new HashSet<>();
+		Set<V> children = getDefaultSet();
 		Map<Integer, V> invert = getInverted();
 
 		for (int i = 0; i < matrix.length; i++)
@@ -93,10 +93,10 @@ public class MatrixGraph<V> extends GraphDirected<V> {
 	}
 
 	@Override
-	public Collection<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
+	public Set<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
 		checkVert(vertex);
 		int x = map.get(vertex);
-		Collection<V> ancestors = new HashSet<>();
+		Set<V> ancestors = getDefaultSet();
 		Map<Integer, V> invert = getInverted();
 
 		for (int i = 0; i < matrix.length; i++)
@@ -189,7 +189,7 @@ public class MatrixGraph<V> extends GraphDirected<V> {
 	}
 
 	private Map<Integer, V> getInverted() {
-		Map<Integer, V> invert = new HashMap<>(map.size() + 1, 1);
+		Map<Integer, V> invert = getDefaultMap();
 		map.forEach((v, i) -> invert.put(i, v));
 		return invert;
 	}

src/main/java/berack96/lib/graph/impl/MatrixUndGraph.java

@@ -8,7 +8,7 @@ import java.util.*;
 
 public class MatrixUndGraph<V> extends GraphUndirected<V> {
 
-    Map<V, Integer> map = new HashMap<>();
+    Map<V, Integer> map = getDefaultMap();
     private int[][] matrix = new int[0][0];
 
     @Override
@@ -73,33 +73,33 @@ public class MatrixUndGraph<V> extends GraphUndirected<V> {
     }
 
     @Override
-    public Collection<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
+    public Set<V> getChildren(V vertex) throws NullPointerException, IllegalArgumentException {
         checkVert(vertex);
-        Collection<V> collection = new HashSet<>();
+        V[] inverted = getInverted();
-        Map<Integer, V> inverted = getInverted();
+        Set<V> set = getDefaultSet();
         int x = map.get(vertex);
         for (int i = 0; i < matrix.length; i++)
             if (i < x && matrix[x][i] != 0)
-                collection.add(inverted.get(i));
+                set.add(inverted[i]);
             else if (i > x && matrix[i][x] != 0)
-                collection.add(inverted.get(i));
+                set.add(inverted[i]);
-        return collection;
+        return set;
     }
 
     @Override
-    public Collection<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
+    public Set<V> getAncestors(V vertex) throws NullPointerException, IllegalArgumentException {
         return getChildren(vertex);
     }
 
     @Override
-    public Collection<Edge<V>> edges() {
+    public Set<Edge<V>> edges() {
-        Map<Integer, V> inverted = getInverted();
+        V[] inverted = getInverted();
-        Collection<Edge<V>> edges = new LinkedList<>();
+        Set<Edge<V>> edges = getDefaultSet();
 
         for (int i = 0; i < matrix.length; i++)
             for (int j = 0; j < matrix[i].length; j++)
                 if (matrix[i][j] != NO_EDGE)
-                    edges.add(new Edge<>(inverted.get(i), inverted.get(j), matrix[i][j]));
+                    edges.add(new Edge<>(inverted[i], inverted[j], matrix[i][j]));
         return edges;
     }
 
@@ -168,9 +168,10 @@ public class MatrixUndGraph<V> extends GraphUndirected<V> {
         return newMatrix;
     }
 
-    private Map<Integer, V> getInverted() {
+    @SuppressWarnings("unchecked")
-        Map<Integer, V> invert = new HashMap<>(map.size() + 1, 1);
+    private V[] getInverted() {
-        map.forEach((v, i) -> invert.put(i, v));
+        V[] invert = (V[]) new Object[map.size()];
+        map.forEach((v, i) -> invert[i] = v);
         return invert;
     }
 }

src/main/java/berack96/lib/graph/models/GraphSaveStructure.java

@@ -31,7 +31,7 @@ public class GraphSaveStructure<V> {
 	 * @throws FileNotFoundException in the case the file is not found
 	 * @throws NullPointerException  in the case the graph is null
 	 */
-	public final void load(@SuppressWarnings("ConstantConditions") Graph<V> graph, String fileName, Class<V> classV) throws FileNotFoundException, NullPointerException {
+	public final void load(Graph<V> graph, String fileName, Class<V> classV) throws FileNotFoundException, NullPointerException {
 		//this way i use this class for the load
 		InstanceCreator<GraphSaveStructure<V>> creator = type -> this;
 		Gson gson = new GsonBuilder().registerTypeAdapter(this.getClass(), creator).create();

src/main/java/berack96/lib/graph/struct/QuickFind.java

@@ -1,19 +1,20 @@
 package berack96.lib.graph.struct;
 
 import java.util.Collection;
-import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 
+import berack96.lib.graph.Graph;
+
 /**
  * Simple implementation of the {@link UnionFind} interface with priority to the find function.
  *
  * @param <X> the elements to search and merge
  */
 public class QuickFind<X> implements UnionFind<X> {
-    Map<X, Collection<X>> struct = new HashMap<>();
+    Map<X, Collection<X>> struct = Graph.getDefaultMap();
 
     @Override
     public int size() {
@@ -22,7 +23,7 @@ public class QuickFind<X> implements UnionFind<X> {
 
     @Override
     public void makeSetAll(Collection<X> elements) throws NullPointerException {
-        Map<X, Collection<X>> temp = new HashMap<>(elements.size() + 1, 1);
+        Map<X, Collection<X>> temp = Graph.getDefaultMap();
         for (X elem : elements)
             temp.computeIfAbsent(elem, new AddElement());
         struct.putAll(temp);
@@ -65,10 +66,10 @@ public class QuickFind<X> implements UnionFind<X> {
     /**
      * Stupid class for implementing the adding of a new element
      */
-    private class AddElement implements Function<X, Collection<X>> {
+    private class AddElement implements Function<X, Set<X>> {
         @Override
-        public Collection<X> apply(X x) {
+        public Set<X> apply(X x) {
-            Collection<X> coll = new HashSet<>();
+            Set<X> coll = Graph.getDefaultSet();
             coll.add(x);
             return coll;
         }

src/main/java/berack96/lib/graph/view/GraphInfo.java

@@ -74,13 +74,13 @@ public class GraphInfo<V> extends JPanel {
         components.add(vNumber);
         components.add(new JLabel("Edge Number: "));
         components.add(eNumber);
-        components.add(new JLabel("Is Cyclic: "));
+        //components.add(new JLabel("Is Cyclic: "));
         //components.add(gCyclic);
 
         JPanel panelInfo = new JPanel();
         panelInfo.setOpaque(false);
         panelInfo.setBorder(BorderFactory.createLineBorder(Color.RED));
-        panelInfo.setLayout(new GridLayout(components.size()/2, 2, 2*2, 2*2));
+        panelInfo.setLayout(new GridLayout(components.size()/2, 2));
         components.forEach(panelInfo::add);
         components.clear();
 
@@ -123,7 +123,7 @@ public class GraphInfo<V> extends JPanel {
         
         JPanel panelVertex = new JPanel();
         panelVertex.setOpaque(false);
-        panelVertex.setLayout(new GridLayout(components.size()/2, 2, 2*2, 2*2));
+        panelVertex.setLayout(new GridLayout(components.size()/2, 2));
         components.forEach(panelVertex::add);
         components.clear();
 
@@ -163,7 +163,7 @@ public class GraphInfo<V> extends JPanel {
         JPanel panelSave = new JPanel();
         panelSave.setOpaque(false);
         panelSave.setBorder(BorderFactory.createLineBorder(Color.RED));
-        panelSave.setLayout(new GridLayout(components.size()/2, 2, 2*2, 2*2));
+        panelSave.setLayout(new GridLayout(components.size()/2, 2));
         components.forEach(panelSave::add);
         components.clear();
 
@@ -177,7 +177,6 @@ public class GraphInfo<V> extends JPanel {
         this.add(panelVertex);
         this.add(panelErrors);
         this.add(panelSave);
-        /*this.add(panelSave);*/
 
         modVertex.doClick();
 

src/main/java/berack96/lib/graph/visit/VisitMST.java

@@ -2,7 +2,7 @@ package berack96.lib.graph.visit;
 
 import berack96.lib.graph.Edge;
 
-import java.util.Collection;
+import java.util.Set;
 
 /**
  * @param <V>
@@ -10,10 +10,11 @@ import java.util.Collection;
 public interface VisitMST<V> extends VisitStrategy<V> {
 
     /**
-     * Return the latest calculated MST.
+     * Return the latest calculated MST.<br>
+     * https://en.wikipedia.org/wiki/Minimum_spanning_tree
      *
      * @return the latest MST
      * @throws NullPointerException if there is no last calculated MST
      */
-    Collection<Edge<V>> getMST();
+    Set<Edge<V>> getMST();
 }

src/main/java/berack96/lib/graph/visit/VisitSCC.java

@@ -1,6 +1,6 @@
 package berack96.lib.graph.visit;
 
-import java.util.Collection;
+import java.util.Set;
 
 /**
  * Interface that is helpful for implements visit that needs to retrieve the SCC
@@ -16,5 +16,5 @@ public interface VisitSCC<V> extends VisitStrategy<V> {
      * @return the latest SCC
      * @throws NullPointerException if there is no last calculated SCC
      */
-    Collection<Collection<V>> getSCC();
+    Set<Set<V>> getSCC();
 }

src/main/java/berack96/lib/graph/visit/impl/Dijkstra.java

@@ -32,8 +32,8 @@ public class Dijkstra<V> implements VisitDistance<V> {
     public VisitInfo<V> visit(Graph<V> graph, V source, Consumer<V> visit) throws NullPointerException, IllegalArgumentException {
         VisitInfo<V> info = new VisitInfo<>(source);
         Queue<QueueEntry> queue = new PriorityQueue<>();
-        Map<V, Integer> dist = new HashMap<>();
+        Map<V, Integer> dist = Graph.getDefaultMap();
-        Map<V, V> prev = new HashMap<>();
+        Map<V, V> prev = Graph.getDefaultMap();
 
         this.source = source;
         dist.put(source, 0);                // Initialization
@@ -63,7 +63,7 @@ public class Dijkstra<V> implements VisitDistance<V> {
         }
 
         /* Cleaning up the results */
-        distance = new HashMap<>();
+        distance = Graph.getDefaultMap();
         for (V vertex : prev.keySet()) {
             List<Edge<V>> path = new LinkedList<>();
             V child = vertex;

src/main/java/berack96/lib/graph/visit/impl/Kruskal.java

@@ -17,10 +17,10 @@ import java.util.function.Consumer;
  * @param <V> The vertex of the graph
  */
 public class Kruskal<V> implements VisitMST<V> {
-    private Collection<Edge<V>> mst;
+    private Set<Edge<V>> mst;
 
     @Override
-    public Collection<Edge<V>> getMST() {
+    public Set<Edge<V>> getMST() {
         return mst;
     }
 
@@ -32,7 +32,7 @@ public class Kruskal<V> implements VisitMST<V> {
         List<Edge<V>> edges = new ArrayList<>(graph.edges());
         Collections.sort(edges);
 
-        mst = new HashSet<>(graph.size(), 1);
+        mst = Graph.getDefaultSet();
         Iterator<Edge<V>> iter = edges.iterator();
         while (iter.hasNext() && sets.size() > 1) {
             Edge<V> edge = iter.next();

src/main/java/berack96/lib/graph/visit/impl/Prim.java

@@ -5,8 +5,7 @@ import berack96.lib.graph.Graph;
 import berack96.lib.graph.GraphUndirected;
 import berack96.lib.graph.visit.VisitMST;
 
-import java.util.Collection;
+import java.util.Set;
-import java.util.LinkedList;
 import java.util.function.Consumer;
 
 /**
@@ -17,17 +16,17 @@ import java.util.function.Consumer;
  */
 public class Prim<V> implements VisitMST<V> {
 
-    private Collection<Edge<V>> mst;
+    private Set<Edge<V>> mst;
 
     @Override
-    public Collection<Edge<V>> getMST() {
+    public Set<Edge<V>> getMST() {
         return mst;
     }
 
     @Override
     public VisitInfo<V> visit(Graph<V> graph, V source, Consumer<V> visit) throws NullPointerException, UnsupportedOperationException {
-        mst = new LinkedList<>();
+        mst = Graph.getDefaultSet();
-        Collection<V> vertices = graph.vertices();
+        Set<V> vertices = graph.vertices();
 
         if (source == null)
             source = vertices.iterator().next();

src/main/java/berack96/lib/graph/visit/impl/Tarjan.java

@@ -15,7 +15,7 @@ import java.util.function.Consumer;
  */
 public class Tarjan<V> implements VisitSCC<V>, VisitTopological<V> {
 
-    private Collection<Collection<V>> SCC = null;
+    private Set<Set<V>> SCC = null;
     private List<V> topologicalSort = null;
 
     private Map<V, Integer> indices = null;
@@ -24,7 +24,7 @@ public class Tarjan<V> implements VisitSCC<V>, VisitTopological<V> {
     private VisitInfo<V> info = null;
 
     @Override
-    public Collection<Collection<V>> getSCC() {
+    public Set<Set<V>> getSCC() {
         return SCC;
     }
 
@@ -44,12 +44,12 @@ public class Tarjan<V> implements VisitSCC<V>, VisitTopological<V> {
      */
     @Override
     public VisitInfo<V> visit(Graph<V> graph, V source, Consumer<V> visit) throws NullPointerException, IllegalArgumentException {
-        SCC = new HashSet<>();
+        SCC = Graph.getDefaultSet();
         topologicalSort = new ArrayList<>(graph.size());
         info = null;
 
-        indices = new HashMap<>();
+        indices = Graph.getDefaultMap();
-        lowLink = new HashMap<>();
+        lowLink = Graph.getDefaultMap();
         stack = new Stack<>();
         int index = 0;
 
@@ -89,7 +89,7 @@ public class Tarjan<V> implements VisitSCC<V>, VisitTopological<V> {
 
         // If v is a root node, pop the stack and generate an SCC
         if (lowLink.get(vertex).equals(indices.get(vertex))) {
-            Set<V> newComponent = new HashSet<>();
+            Set<V> newComponent = Graph.getDefaultSet();
             V temp;
             do {
                 temp = stack.pop();

src/test/java/berack96/test/lib/TestGraph.java

@@ -23,6 +23,7 @@ import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.PrintStream;
 import java.io.UnsupportedEncodingException;
+import java.net.URISyntaxException;
 import java.util.*;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Stream;
@@ -1543,11 +1544,27 @@ public class TestGraph {
                 new Edge<>("5", "4", 5),
                 new Edge<>("6", "2", 2));
 
+        sub = graph.subGraph("even", "even");
+        shouldContain(sub.vertices(), "2", "4", "6");
+        shouldContain(sub.edges(),
+                new Edge<>("4", "6", 6),
+                new Edge<>("6", "2", 2));
+        
+        sub = graph.subGraph("even", null, "even");
+        shouldContain(sub.vertices(), "2", "4", "6");
+        shouldContain(sub.edges(),
+                new Edge<>("4", "6", 6),
+                new Edge<>("6", "2", 2));
+
+        sub = graph.subGraph((Object) null);
+        shouldContain(sub.vertices(), "7", "8");
+        shouldContain(sub.edges(), new Edge<>("8", "7", 9));
+        
         sub = graph.subGraph();
         shouldContain(sub.vertices(), "7", "8");
         shouldContain(sub.edges(), new Edge<>("8", "7", 9));
 
-        sub = graph.subGraph(null);
+        sub = graph.subGraph((Object[]) null);
         shouldContain(sub.vertices(), "7", "8");
         shouldContain(sub.edges(), new Edge<>("8", "7", 9));
     }
@@ -1672,7 +1689,7 @@ public class TestGraph {
     //TODO tests for GraphUndirected save/load
     @ParameterizedTest
     @MethodSource("getGraphsDir")
-    public void saveLoadDir(final GraphDirected<String> graph) {
+    public void saveLoadDir(final GraphDirected<String> graph) throws URISyntaxException {
         /*
          * This graph should be like this
          *
@@ -1682,8 +1699,7 @@ public class TestGraph {
          * v      v
          * 3  <-  5  ->  4      8
          */
-
+        String fileName = ClassLoader.getSystemResource("").getPath() + "resources/test.json";
-        String fileName = "test/resources/test.json";
         Set<String> vertices = Set.of("1", "2", "3", "4", "5", "6", "7", "8");
         Set<Edge<String>> edges = new HashSet<>();
         Map<String, Set<Object>> marks = new HashMap<>();

src/test/java/resources/test.json

@@ -0,0 +1 @@
+{"vertices":["\"6\"","\"5\"","\"4\"","\"3\"","\"2\"","\"1\"","\"8\"","\"7\""],"edges":[{"src":"\"4\"","dest":"\"6\"","weight":6},{"src":"\"2\"","dest":"\"5\"","weight":4},{"src":"\"5\"","dest":"\"4\"","weight":5},{"src":"\"5\"","dest":"\"3\"","weight":2},{"src":"\"1\"","dest":"\"3\"","weight":1},{"src":"\"6\"","dest":"\"2\"","weight":2},{"src":"\"1\"","dest":"\"2\"","weight":1},{"src":"\"8\"","dest":"\"7\"","weight":9}]}

test/resources/test.json

@@ -1,54 +0,0 @@
-{
-  "vertices": [
-    "\"6\"",
-    "\"5\"",
-    "\"4\"",
-    "\"3\"",
-    "\"2\"",
-    "\"1\"",
-    "\"8\"",
-    "\"7\""
-  ],
-  "edges": [
-    {
-      "src": "\"4\"",
-      "dest": "\"6\"",
-      "weight": 6
-    },
-    {
-      "src": "\"2\"",
-      "dest": "\"5\"",
-      "weight": 4
-    },
-    {
-      "src": "\"5\"",
-      "dest": "\"4\"",
-      "weight": 5
-    },
-    {
-      "src": "\"5\"",
-      "dest": "\"3\"",
-      "weight": 2
-    },
-    {
-      "src": "\"1\"",
-      "dest": "\"3\"",
-      "weight": 1
-    },
-    {
-      "src": "\"6\"",
-      "dest": "\"2\"",
-      "weight": 2
-    },
-    {
-      "src": "\"1\"",
-      "dest": "\"2\"",
-      "weight": 1
-    },
-    {
-      "src": "\"8\"",
-      "dest": "\"7\"",
-      "weight": 9
-    }
-  ]
-}