Added my code of

src/main/java/StringManipulation.java

@@ -1,33 +1,128 @@
 public class StringManipulation implements StringManipulationInterface {
 
+    private String _string;
+
     @Override
     public String getString() {
-        return null;
+        return _string;
     }
 
     @Override
     public void setString(String string) {
+        _string = string;
     }
 
     @Override
     public int count() {
-        return 0;
+
+        String string = getString();
+        if (string.isBlank()){
+            return 0;
+        }
+        String[] words = string.split("\\s+");
+        return words.length;
+
     }
 
     @Override
     public String removeNthCharacter(int n, boolean maintainSpacing) {
-        return null;
+        String string = getString();
+        StringBuilder result = new StringBuilder();
+
+        // exception throw IndexOutOfBoundsException
+        if (n > string.length()) {
+            throw new IndexOutOfBoundsException("n is more then string ");
+        }
+        // exception throw IllegalArgumentException
+        if (n <= 0) {
+            throw new IllegalArgumentException("n is less then or equal to zero");
+        }
+
+        int  target_n = n;
+        for (int i = 0; i < string.length(); i++) {
+
+            // gets character
+            char c = string.charAt(i);
+
+            // if i is not equal to n then it add charter
+            if (i != target_n-1) {
+                result.append(c);
+
+            }
+            else {
+                if(maintainSpacing) {
+
+                    result.append(' ');
+
+                }
+                target_n += n;
+            }
+
+
+        }
+        return result.toString();
     }
 
     @Override
     public String[] getSubStrings(int startWord, int endWord) {
-        return null;
+        // get number of words
+        int numberOfWords = count();
+        String string = getString();
+        String[] words = string.split("\\s+");
+
+
+        // exception throw IndexOutOfBoundsException
+
+        if (numberOfWords < endWord) {
+            throw new IndexOutOfBoundsException("string has less then endword  ");
+        }
+        // exception throw IllegalArgumentException
+
+        if (startWord <= 0 || endWord <= 0 || startWord > endWord) {
+            throw new IllegalArgumentException("startword or endword is invalid ");
+        }
+
+        String[] substrings = new String[endWord - startWord + 1];
+
+        int count = 0;
+        for (int i = startWord-1; i <= endWord-1;i++){
+            substrings[count] = words[i];
+            count++;
+        }
+        return substrings;
     }
 
     @Override
     public String restoreString(int[] indices) {
-        return null;
-    }
+        String string = getString();
+        int stringSize = string.length();
+
+        System.out.println("The count is: " + stringSize+ "indices.length = "+indices.length);
+
+
+        // exception throw IllegalArgumentException
+
+        if (stringSize != indices.length ) {
+            throw new IllegalArgumentException("length of indices does not match string length ");
+        }
 
 
+
+        char[] stringOutPut = new char[indices.length];
+
+        for (int i = 0; i < stringSize; i++) {
+            int index = indices[i];
+
+
+            // exception throw IndexOutOfBoundsException
+            //indices.length
+            if (index < 0 || index >= stringSize) {
+                throw new IndexOutOfBoundsException("string has less then endword  ");
+            }
+
+            stringOutPut[i] = string.charAt(index);
+
+        }
+        return new String(stringOutPut);
+    }
 }