finished

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

 package rocks.zipcode;
 
 import java.io.IOException;
+import java.util.regex.Pattern;
 
 /**
  * @author leon on 16/11/2018.
 
     @Override
     public void write(String contentToBeWritten) {
+        if (isAlpha(contentToBeWritten)) {
+            super.write(contentToBeWritten);
+        } else {
+            throw new IllegalArgumentException();
+        }
     }
 
     private Boolean isAlpha(String s) {
-        return null;
+        return Pattern.matches("^[a-zA-Z\\s]+$", s);
     }
 }

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

 
 import java.io.*;
 import java.nio.file.Files;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
 
     @Override
     public void write(String contentToBeWritten) {
+        try {
+            BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(file));
+            bufferedWriter.write(contentToBeWritten);
+            bufferedWriter.close();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
     }
 
     @Override
     public void write(Integer lineNumber, String valueToBeWritten) {
+        String[] array = read().split("\n");
+        array[lineNumber] = valueToBeWritten;
+        String newFile = "";
+        for (String element : array) {
+            newFile += element + "\n";
+        }
+        write(newFile.trim());
     }
 
     @Override
     public String read(Integer lineNumber) {
-        return null;
+        try {
+            BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
+            String line = "";
+            for (int i = 0; i <= lineNumber; i++) {
+                line = bufferedReader.readLine();
+            }
+            bufferedReader.close();
+            return line;
+        } catch (IOException e) {
+            e.printStackTrace();
+            return null;
+        }
     }
 
     @Override
     public String read() {
-        return null;
+        try {
+            BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
+            String stringFile = "";
+            String line;
+            while ((line = bufferedReader.readLine()) != null) {
+                stringFile += line + "\n";
+            }
+            bufferedReader.close();
+            return stringFile.trim();
+        } catch (IOException e) {
+            e.printStackTrace();
+            return null;
+        }
     }
 
     @Override
     public void replaceAll(String stringToReplace, String replacementString) {
+        String newFile = read().replaceAll(stringToReplace, replacementString);
+        write(newFile);
     }
 
     @Override
     public void overWrite(String content) {
+        write(content);
     }
 
     public List<String> toList() {
-        return null;
+        return Arrays.asList(read().split("\n"));
     }
 
     @Override
     public File getFile() {
-        return null;
+        return file;
     }
 
     @Override
     public String toString() {
-        return null;
+        return file + "{" + read() + "}";
     }
 }

src/main/java/rocks/zipcode/NumericCharDocument.java

 package rocks.zipcode;
 
 import java.io.IOException;
+import java.util.regex.Pattern;
 
 /**
  * @author leon on 16/11/2018.
 
     @Override
     public void write(String contentToBeWritten) {
+        if (isNumeric(contentToBeWritten)) {
+            super.write(contentToBeWritten);
+        } else {
+            throw new IllegalArgumentException();
+        }
     }
 
     private Boolean isNumeric(String s) {
-        return null;
+        return Pattern.matches("^[0-9]+$", s);
     }
 }

src/main/java/rocks/zipcode/SpecialCharDocument.java

 package rocks.zipcode;
 
 import java.io.IOException;
+import java.util.regex.Pattern;
 
 /**
  * @author leon on 18/11/2018.
 
     @Override
     public void write(String contentToBeWritten) {
+        if (isSpecialCharacters(contentToBeWritten)) {
+            super.write(contentToBeWritten);
+        } else {
+            throw new IllegalArgumentException();
+        }
     }
 
     private Boolean isSpecialCharacters(String s) {
-        return null;
+        return Pattern.matches("^[\\W_]+$", s);
     }
 }