added more methods

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

     }
 
     @Override
-    public void write(Integer lineNumber, String valueToBeWritten) {
-
+    public void write(Integer lineNumber, String valueToBeWritten){
 
     }
 
     @Override
-    public String read(Integer lineNumber){
-        return null;
-
+    public String read(Integer lineNumber) throws IOException {
+        BufferedReader br = new BufferedReader(new FileReader(file));
+        String stringAtLineNumber;
+        int i = 0;
+        do{
+            stringAtLineNumber = br.readLine();
+            i++;
+
+        } while (i <= lineNumber);
+        return stringAtLineNumber;
     }
 
     @Override
 
     @Override
     public void overWrite(String content) {
+
     }
 
     public List<String> toList() {

src/main/java/rocks/zipcode/DocumentInterface.java

 package rocks.zipcode;
 
 import java.io.File;
+import java.io.IOException;
 import java.util.List;
 
 /**
 public interface DocumentInterface {
     void write(String contentToBeWritten);
 
-    void write(Integer lineNumber, String valueToBeWritten);
+    void write(Integer lineNumber, String valueToBeWritten) throws Exception;
 
-    String read(Integer lineNumber);
+    String read(Integer lineNumber) throws Exception;
 
     String read() throws Exception;