updating

src/main/java/rocks/zipcode/AlphaCharDocument.java

@@ -15,6 +15,7 @@ public class AlphaCharDocument extends Document {
     }
 
     private Boolean isAlpha(String s) {
+
         return null;
     }
 }

src/main/java/rocks/zipcode/Document.java

@@ -37,7 +37,16 @@ public class Document implements DocumentInterface {
 
     @Override
     public String read() {
-        return null;
+        StringBuilder builder = new StringBuilder();
+        try (BufferedReader br = new BufferedReader(new FileReader(file))) {
+            String sCurrentLine;
+            while ((sCurrentLine = br.readLine()) != null) {
+                builder.append(sCurrentLine).append("\n");
+            }
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return builder.toString().trim();
     }
 
     @Override