diff --git a/DataStructures/Queues/Queues.java b/DataStructures/Queues/Queues.java
index f9bb42e4a..d5b9a8e5c 100644
--- a/DataStructures/Queues/Queues.java
+++ b/DataStructures/Queues/Queues.java
@@ -9,6 +9,11 @@ package DataStructures.Queues;
  *
  */
 class Queue {
+    /**
+     * Default initial capacity.
+     */
+    private static final int DEFAULT_CAPACITY = 10;
+
     /**
      * Max size of the queue
      */
@@ -30,6 +35,13 @@ class Queue {
      */
     private int nItems;
 
+    /**
+     * init with DEFAULT_CAPACITY
+     */
+    public Queue() {
+        this(DEFAULT_CAPACITY);
+    }
+
     /**
      * Constructor
      *
diff --git a/DataStructures/Stacks/StackArray.java b/DataStructures/Stacks/StackArray.java
index cc8596293..88da42cd3 100644
--- a/DataStructures/Stacks/StackArray.java
+++ b/DataStructures/Stacks/StackArray.java
@@ -34,6 +34,11 @@ public class StackArray {
         System.out.println(myStackArray.peek()); // will print 2
     }
 
+    /**
+     * Default initial capacity.
+     */
+    private static final int DEFAULT_CAPACITY = 10;
+
     /**
      * The max size of the Stack
      */
@@ -49,6 +54,13 @@ public class StackArray {
      */
     private int top;
 
+    /**
+     * init Stack with DEFAULT_CAPACITY
+     */
+    public StackArray() {
+        this(DEFAULT_CAPACITY);
+    }
+    
     /**
      * Constructor
      *