added all java files

src/main/java/StringManipulation.java

@@ -1,33 +1,122 @@
 public class StringManipulation implements StringManipulationInterface {
 
+    private String string;
+
     @Override
     public String getString() {
-        return null;
+        return string;
     }
 
     @Override
     public void setString(String string) {
+        this.string = string;
     }
 
     @Override
     public int count() {
-        return 0;
+        if (string == null || string.isEmpty()) {
+            return 0;
+        }
+
+        String trimmedString = string.trim();
+        if (trimmedString.isEmpty()) {
+            return 0;
+        }
+
+        // Split the string by whitespace to get individual words
+        String[] words = trimmedString.split("\\s+");
+
+        return words.length;
     }
 
+
+
     @Override
     public String removeNthCharacter(int n, boolean maintainSpacing) {
-        return null;
-    }
+    	 if (n <= 0) {
+             throw new IllegalArgumentException("Error: n is less than or equal to 0");
+         } 
+    	 else if (string == null) {
+             throw new NullPointerException("Error: String has not been initialized");
+         } 
+    	 else if (n > string.length()) {
+             throw new IndexOutOfBoundsException("Error: n exceeds string length");
+         }
+
+
+    	StringBuilder result = new StringBuilder();
+        int count = 0;  
+        for (int i = 0; i < string.length(); i++) {
+            char currentChar = string.charAt(i);
+            count++;
+                if (count % n == 0 && maintainSpacing) {
+                result.append(' ');
+            }    
+            if (count % n != 0) {
+                result.append(currentChar);
+            }
+
+
+        }
+
+        return result.toString();
+        }
+
+
+
+
 
     @Override
     public String[] getSubStrings(int startWord, int endWord) {
-        return null;
+        if (string == null) {
+        	throw new NullPointerException("Error: string is not yet initialized");
+        }
+        String[] words = string.trim().split("\\s+");
+        if(startWord <= 0 || endWord <= 0) {
+        	throw new IllegalArgumentException("Error: start index and end index is less than 1");
+        }
+
+        else if (startWord > endWord) {
+            throw new IndexOutOfBoundsException("Error: start index is larger than end");
+        }
+
+        else if (endWord > words.length) {
+            throw new IndexOutOfBoundsException("Error: end index is larger than the string length");
+        }
+
+        int substringsCount = endWord - startWord + 1;
+        String[] substrings = new String[substringsCount];
+
+        int index = 0;
+        for (int i = startWord - 1; i < endWord; i++) {
+            substrings[index++] = words[i];
+        }
+
+        return substrings;
     }
 
     @Override
     public String restoreString(int[] indices) {
-        return null;
-    }
+    	if (string == null) {
+            throw new NullPointerException("Error: string is not yet initialized");
+        }
 
-
-}
+        if (indices.length != string.length()) {
+            throw new IllegalArgumentException("Error: string length is not equal to indices length");
+        }
+        for (int i = 0; i < indices.length - 1; i++) {     
+            for (int j = i + 1; j < indices.length; j++) {
+                if (indices[i] == indices[j]) {
+                    throw new IllegalArgumentException("Error: some indexes are not unique");
+                }
+            }
+        }
+
+        char[] restored = new char[indices.length];
+        for (int i = 0; i < indices.length; i++) {
+
+            restored[i] = string.charAt(indices[i]);
+        }
+        return new String(restored);
+    }
+}

src/main/java/StringManipulationInterface.java

@@ -79,10 +79,10 @@ public interface StringManipulationInterface {
      * The string s will be shuffled such that the character at the ith position moves to indices[i] in the shuffled string.
      * Return the shuffled string.
      * example:
-     * Input: string = "UnitTest", indices = [4,5,6,7,0,1,2,3]
+     * Input: string = "UnitTest", indices = [4,5,6,7,0,2,1,3]
      * Output: "TestUnit"
      * Explanation:
-     * indices: 4 5 6 7 0 1 2 3
+     * indices: 4 5 6 7 0 2 1 3
      * String:  U n i t T e s t
      * Actions to Shuffle: Shift U to 4th position, n to 5th position, i to 6th position ......
      * Output: T e s t U n i t
@@ -95,7 +95,7 @@ public interface StringManipulationInterface {
      * indices length is the same as the string length.
      *
      * throws IllegalArgumentException if not s.length == indices.length == n
-     * throws IndexOutOfBoundsException if   indices[i]< 0  or  indices[i]>= string length
+     * throws IndexOutOfBoundsException if   indices[i]< 0  or  indices[i]> string length
      *
      * @param indices is an integer array for shuffled string new indices positions
      * the character at the ith position moves to indices[i] in the shuffled string.