minor fix

data-structures/src/main/java/com/baeldung/graph/Graph.java

@@ -2,6 +2,7 @@ package com.baeldung.graph;
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Stack;
@@ -29,7 +30,7 @@ public class Graph {
         while (!stack.isEmpty()) {
             int current = stack.pop();
             isVisited[current] = true;
-            System.out.print(" " + current);
+            visit(current);
             for (int dest : adjVertices.get(current)) {
                 if (!isVisited[dest])
                     stack.push(dest);
@@ -44,29 +45,30 @@ public class Graph {
 
     private void dfsRecursive(int current, boolean[] isVisited) {
         isVisited[current] = true;
-        System.out.print(" " + current);
+        visit(current);
         for (int dest : adjVertices.get(current)) {
             if (!isVisited[dest])
                 dfsRecursive(dest, isVisited);
         }
     }
 
-    public void topologicalSort(int start) {
-        Stack<Integer> result = new Stack<Integer>();
+    public List<Integer> topologicalSort(int start) {
+        LinkedList<Integer> result = new LinkedList<Integer>();
         boolean[] isVisited = new boolean[adjVertices.size()];
         topologicalSortRecursive(start, isVisited, result);
-        while (!result.isEmpty()) {
-            System.out.print(" " + result.pop());
-        }
+        return result;
     }
 
-    private void topologicalSortRecursive(int current, boolean[] isVisited, Stack<Integer> result) {
+    private void topologicalSortRecursive(int current, boolean[] isVisited, LinkedList<Integer> result) {
         isVisited[current] = true;
         for (int dest : adjVertices.get(current)) {
             if (!isVisited[dest])
                 topologicalSortRecursive(dest, isVisited, result);
         }
-        result.push(current);
+        result.addFirst(current);
     }
 
+    private void visit(int value) {
+        System.out.print(" " + value);        
+    }
 }

data-structures/src/main/java/com/baeldung/tree/BinaryTree.java

@@ -103,14 +103,14 @@ public class BinaryTree {
     public void traverseInOrder(Node node) {
         if (node != null) {
             traverseInOrder(node.left);
-            System.out.print(" " + node.value);
+            visit(node.value);
             traverseInOrder(node.right);
         }
     }
 
     public void traversePreOrder(Node node) {
         if (node != null) {
-            System.out.print(" " + node.value);
+            visit(node.value);
             traversePreOrder(node.left);
             traversePreOrder(node.right);
         }
@@ -120,7 +120,7 @@ public class BinaryTree {
         if (node != null) {
             traversePostOrder(node.left);
             traversePostOrder(node.right);
-            System.out.print(" " + node.value);
+            visit(node.value);
         }
     }
 
@@ -159,7 +159,7 @@ public class BinaryTree {
                 stack.push(current);                
             }
             current = stack.pop();
-            System.out.print(" " + current.value);
+            visit(current.value);
             if(current.right != null) {
                 current = current.right;                
                 stack.push(current);
@@ -173,7 +173,7 @@ public class BinaryTree {
         stack.push(root);
         while(! stack.isEmpty()) {
             current = stack.pop();
-            System.out.print(" " + current.value);
+            visit(current.value);
             
             if(current.right != null)
                 stack.push(current.right);
@@ -196,7 +196,7 @@ public class BinaryTree {
 
             if (!hasChild || isPrevLastChild) {
                 current = stack.pop();
-                System.out.print(" " + current.value);
+                visit(current.value);
                 prev = current;
             } else {
                 if (current.right != null) {
@@ -209,6 +209,9 @@ public class BinaryTree {
         }   
     }    
     
+    private void visit(int value) {
+        System.out.print(" " + value);        
+    }
     
     class Node {
         int value;

data-structures/src/test/java/com/baeldung/graph/GraphUnitTest.java

@@ -1,5 +1,7 @@
 package com.baeldung.graph;
 
+import java.util.List;
+
 import org.junit.Test;
 
 public class GraphUnitTest {
@@ -15,7 +17,8 @@ public class GraphUnitTest {
     @Test
     public void givenDirectedGraph_whenGetTopologicalSort_thenPrintValuesSorted() {
         Graph graph = createDirectedGraph();
-        graph.topologicalSort(0);
+        List<Integer> list = graph.topologicalSort(0);
+        System.out.println(list);
     }
 
     private Graph createDirectedGraph() {