diff --git a/source/ch6_definingclasses.ptx b/source/ch6_definingclasses.ptx
index 252ec9b..185851a 100644
--- a/source/ch6_definingclasses.ptx
+++ b/source/ch6_definingclasses.ptx
@@ -200,11 +200,11 @@ public void setDenominator(Integer denominator) {
             In Java, <term>constructors</term> have the same name as the class and are declared public.
             They are declared without a return type.
             So any method that is named the same as the class and has no return type is a constructor.
-            Our constructor will take two parameters: the numerator and the denominator.
+            Our constructor will take two parameters: the numerator and the denominator. <xref ref="java-fraction-constructor" text="type-global"/> shows the constructor for the <c>Fraction</c> class.
         </p>
 
-
-        <program xml:id="java-fraction-constructor" language="java">
+        <listing xml:id="java-fraction-constructor">
+        <program interactive="activecode" language="java">
             <code>
 public Fraction(Integer top, Integer bottom) {
     num = top;
@@ -212,6 +212,7 @@ public Fraction(Integer top, Integer bottom) {
 }
             </code>
         </program>
+        </listing>
 
         <p>
             <idx><c>this</c></idx>
@@ -221,11 +222,11 @@ public Fraction(Integer top, Integer bottom) {
             This allows the Java compiler to do the work of dereferencing the current Java object.
             Java does provide a special variable called <c>this</c> that works like the <c>self</c> variable.
             In Java, <c>this</c> is typically only used when it is needed to differentiate between a parameter or local variable and an instance variable.
-            For example this alternate definition of the the Fraction constructor uses <c>this</c> to differentiate between parameters and instance variables.
+            For example,<xref ref="java-fraction-constructor" text="type-global"/> shows an alternate definition of the the Fraction constructor that uses <c>this</c> to differentiate between parameters and instance variables.
         </p>
 
-
-        <program xml:id="java-fraction-class-this" language="java">
+        <listing xml:id="java-fraction-class-this">
+        <program interactive="activecode" language="java">
             <code>
 public Fraction(Integer num, Integer den) {
     this.num = num;
@@ -233,6 +234,7 @@ public Fraction(Integer num, Integer den) {
 }
             </code>
         </program>
+        </listing>
     </section>
 
     <section xml:id="methods">