added listing to txt

Author: habibasorour

source/ch8_filehandling.ptx

@@ -7,7 +7,7 @@
     <section xml:id="class-imports">
         <title>Class Imports</title>
         <p>
-            File handling is an integral part of programming. Most programming languages have the ability to create, read from, write to, and delete, files. In Python, most built-in libraries are available without needing  to explicitly import additional packages, but some libraries like <c>math</c> do need to be imported. Consider the following.
+            File handling is an integral part of programming. Most programming languages have the ability to create, read from, write to, and delete, files. In Python, most built-in libraries are available without needing  to explicitly import additional packages, but some libraries like <c>math</c> do need to be imported. <xref ref="file-class-import-Python-example" text="type-global"/> shows an example of importing the <c>math</c> library in Python.
         </p>
 
         <listing  xml:id = "file-class-import-Python-example">
@@ -20,10 +20,10 @@
         </listing>
 
         <p>
-            Delete the first line that says <c>import math</c> and see what happens. The <c>import math</c> is needed. The same program in Java would look like this:
+            Delete the first line that says <c>import math</c> and see what happens. The <c>import math</c> is needed. The same program in Java would look like <xref ref="file-class-import-Java-example" text="type-global"/>.
         </p>
 
-        <listing  xml:id = "file-class-import-Java-example">
+        <listing  xml:id ="file-class-import-Java-example">
         <program interactive="activecode" language="java">
             <code>
             import java.lang.Math;
@@ -42,7 +42,7 @@
         </p>
 
         <p>
-            Much like the <c>Math</c> class, in order for your program to work with files you need use <c>import</c>. Java includes a class called <c>File</c> in the <c>io</c> library. This class allows you to create <c>File</c> objects, and use its public methods. 
+            Much like the <c>Math</c> class, in order for your program to work with files you need use <c>import</c>. Java includes a class called <c>File</c> in the <c>io</c> library shown in <xref ref="io-file-import" text="type-global"/>. This class allows you to create <c>File</c> objects, and use its public methods. 
         </p>
 
         <listing  xml:id = "io-file-import">
@@ -52,7 +52,7 @@
         </listing>
 
         <p>
-            The <c>Scanner</c> class from the <c>util</c> library will need to be imported if there is any need for a program to read a file. It should be noted that this library is unnecessary if the program will not be reading any data from a file.
+            The <c>Scanner</c> class from the <c>util</c> library will need to be imported if there is any need for a program to read a file as shown in <xref ref="util-scanner-import" text="type-global"/>. It should be noted that this library is unnecessary if the program will not be reading any data from a file.
         </p>
         <listing  xml:id = "util-scanner-import">
         <program>
@@ -61,7 +61,7 @@
         </listing>
 
         <p>
-            The <c>FileWriter</c> class can be used to write to files. In the same way that the <c>Scanner</c> class isn't needed unless the program will read from a file, the <c>FileWriter</c> class isn't needed unless the program will write to a file.
+            The <c>FileWriter</c> class can be used to write to files as shown in <xref ref="io-filewriter-import" text="type-global"/>. In the same way that the <c>Scanner</c> class isn't needed unless the program will read from a file, the <c>FileWriter</c> class isn't needed unless the program will write to a file.
         </p>
 
         <listing  xml:id = "io-filewriter-import">
@@ -71,7 +71,7 @@
         </listing>
 
         <p>
-            Finally, these last two classes provide error handling and must be used in tandem with the <c>File</c> class when reading from or writing to files. <c>IOException</c> handles file creation and writing errors, while <c>FileNotFoundException</c> handles errors when trying to read files. 
+            Finally, these last two classes provide error handling and must be used in tandem with the <c>File</c> class when reading from or writing to files as shown in <xref ref="io-exception-imports" text="type-global"/>. <c>IOException</c> handles file creation and writing errors, while <c>FileNotFoundException</c> handles errors when trying to read files. 
         </p>
 
         <listing  xml:id = "io-exception-imports">