diff --git a/sl_11/PrimeNumber.java b/sl_11/PrimeNumber.java
new file mode 100644
index 0000000..f9ff341
--- /dev/null
+++ b/sl_11/PrimeNumber.java
@@ -0,0 +1,23 @@
+import java.util.Scanner;
+
+public class PrimeNumber {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter a number: ");
+        int number = scanner.nextInt();
+        boolean isPrime = number > 1;
+
+        for (int divisor = 2; divisor * divisor <= number && isPrime; divisor++) {
+            if (number % divisor == 0) {
+                isPrime = false;
+            }
+        }
+
+        if (isPrime) {
+            System.out.println(number + " is a prime number.");
+        } else {
+            System.out.println(number + " is not a prime number.");
+        }
+        scanner.close();
+    }
+}
\ No newline at end of file
diff --git a/sl_12/StringMutability.java b/sl_12/StringMutability.java
new file mode 100644
index 0000000..d009c19
--- /dev/null
+++ b/sl_12/StringMutability.java
@@ -0,0 +1,18 @@
+public class StringMutability {
+    public static void main(String[] args) {
+        String text = "Java";
+        String changedText = text.concat(" Language");
+
+        StringBuffer buffer = new StringBuffer("Java");
+        buffer.append(" Language");
+
+        StringBuilder builder = new StringBuilder("Java");
+        builder.append(" Language");
+
+        System.out.println("Original String: " + text);
+        System.out.println("New String after concat: " + changedText);
+        System.out.println("String remains unchanged: " + text);
+        System.out.println("Mutable StringBuffer: " + buffer);
+        System.out.println("Mutable StringBuilder: " + builder);
+    }
+}
\ No newline at end of file
diff --git a/sl_13/StringPalindrome.java b/sl_13/StringPalindrome.java
new file mode 100644
index 0000000..4720003
--- /dev/null
+++ b/sl_13/StringPalindrome.java
@@ -0,0 +1,18 @@
+import java.util.Scanner;
+
+public class StringPalindrome {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter a string: ");
+        String input = scanner.nextLine();
+        String normalized = input.replaceAll("\\s+", "").toLowerCase();
+        String reversed = new StringBuilder(normalized).reverse().toString();
+
+        if (normalized.equals(reversed)) {
+            System.out.println("The string is a palindrome.");
+        } else {
+            System.out.println("The string is not a palindrome.");
+        }
+        scanner.close();
+    }
+}
\ No newline at end of file
diff --git a/sl_14/CharacterOccurrence.java b/sl_14/CharacterOccurrence.java
new file mode 100644
index 0000000..ab929e3
--- /dev/null
+++ b/sl_14/CharacterOccurrence.java
@@ -0,0 +1,21 @@
+import java.util.Scanner;
+
+public class CharacterOccurrence {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter a string: ");
+        String text = scanner.nextLine();
+        System.out.print("Enter the character to count: ");
+        char target = scanner.nextLine().charAt(0);
+        int count = 0;
+
+        for (int i = 0; i < text.length(); i++) {
+            if (text.charAt(i) == target) {
+                count++;
+            }
+        }
+
+        System.out.println("Occurrences of '" + target + "': " + count);
+        scanner.close();
+    }
+}
\ No newline at end of file
diff --git a/sl_15/VowelConsonantCount.java b/sl_15/VowelConsonantCount.java
new file mode 100644
index 0000000..c771e66
--- /dev/null
+++ b/sl_15/VowelConsonantCount.java
@@ -0,0 +1,27 @@
+import java.util.Scanner;
+
+public class VowelConsonantCount {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter a string: ");
+        String text = scanner.nextLine().toLowerCase();
+        int vowels = 0;
+        int consonants = 0;
+
+        for (int i = 0; i < text.length(); i++) {
+            char character = text.charAt(i);
+            if (character >= 'a' && character <= 'z') {
+                if (character == 'a' || character == 'e' || character == 'i'
+                        || character == 'o' || character == 'u') {
+                    vowels++;
+                } else {
+                    consonants++;
+                }
+            }
+        }
+
+        System.out.println("Vowels: " + vowels);
+        System.out.println("Consonants: " + consonants);
+        scanner.close();
+    }
+}
\ No newline at end of file