fixed some mistakes

Author: habibasorour

source/ch6_definingclasses.ptx

@@ -820,7 +820,7 @@ public int compareTo(Fraction other) {
             Suppose that you wanted to write a Student class so that the class could keep track of the number of students it had created.
             Although you could do this with a global counter variable that is an ugly solution.
             The right way to do it is to use a <c>static</c> variable.
-            <xref ref="python-static-member-variable" text="The following Python code"/> shows how to do this in Python.
+            <xref ref="python-static-member-variable" text="type-global"/> shows how to do this in Python.
         </p>
 
         <listing xml:id="python-static-member-variable">    
@@ -842,7 +842,7 @@ main()
         </listing>
 
         <p>
- <xref ref="java-static-member-variable" text="The following Java code"/> shows how to do this in Java. 
+ <xref ref="java-static-member-variable" text="type-global"/> shows how to do this in Java. 
         </p>
 
         <listing xml:id="java-static-member-variable">  
@@ -870,7 +870,7 @@ public class Student {
 
         <p>
             <idx>static member variable</idx>
- In this example notice that we create a <term>static member variable</term> by using the <c>static</c> modifier on the variable declaration. Once a variable has been declared <c>static</c> in Java it can be accessed from inside the class without prefixing the name of the class as we had to do in Python. 
+ In <xref ref="java-static-member-variable" text="type-global"/>, notice that we create a <term>static member variable</term> by using the <c>static</c> modifier on the variable declaration. Once a variable has been declared <c>static</c> in Java it can be accessed from inside the class without prefixing the name of the class as we had to do in Python. 
         </p>
     </section>