extras: add P16-P23, P25

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

P16.java

@@ -0,0 +1,5 @@
+public class P16 {
+    public static void main(String[] args) {
+        System.out.println("Hello World");
+    }
+}

P17.java

@@ -0,0 +1,9 @@
+public class P17 {
+    public static void main(String[] args) {
+        int a = 5;
+        int b = 6;
+        int c = a + b;
+
+        System.out.print(c);
+    }
+}

P18.java

@@ -0,0 +1,11 @@
+public class P18 {
+  public static void main(String[] _args) {
+      int a = 5, b, f;
+      b = f = a;
+
+      while (b-- > 1)
+          f *= b;
+
+      System.out.println(a + "! = " + f);
+  }
+}

P19.java

@@ -0,0 +1,17 @@
+import java.util.Scanner;
+
+public class P19 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+
+        System.out.print("Enter the first number: ");
+        int a = scanner.nextInt();
+
+        System.out.print("Enter the second number: ");
+        int b = scanner.nextInt();
+
+        System.out.println("Sum: " + (a + b));
+
+        scanner.close();
+    }
+}

P20.java

@@ -0,0 +1,14 @@
+public class P20 {
+    public static void main(String[] args) {
+        int n = 10;
+        System.out.print("Fibonacci Series of length " + n + ": ");
+        fibonacci(0, 1, n);
+    }
+
+    public static void fibonacci(int a, int b, int n) {
+        if (n == 0)
+            return;
+        System.out.print(a + " ");
+        fibonacci(b, a + b, n - 1);
+    }
+}

P21.java

@@ -0,0 +1,23 @@
+import java.util.Scanner;
+
+public class P21 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+
+        System.out.print("Enter a: ");
+        int a = scanner.nextInt();
+
+        System.out.print("Enter b: ");
+        int b = scanner.nextInt();
+
+        System.out.print("Enter c: ");
+        int c = scanner.nextInt();
+
+        if ( a > b && a > c)
+            System.out.print("a is the greatest integer");
+        else if ( b > a && b > c)
+            System.out.print("b is the greatest integer");
+        else
+            System.out.print("c is the greatest integer");
+    }
+}

P22.java

@@ -0,0 +1,25 @@
+import java.util.Scanner;
+
+public class P22 {
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+
+        System.out.print("Enter an integer: ");
+        int n = scanner.nextInt();
+
+        System.out.println(n + " is " + (prime(n) ? "" : "not ") + "a prime number.");
+
+        scanner.close();
+    }
+
+    public static boolean prime(int number) {
+        if (number <= 1)
+            return false;
+
+        for (int i = 2; i <= Math.sqrt(number); i++)
+            if (number % i == 0)
+                return false;
+
+        return true;
+    }
+}

P23.java

@@ -0,0 +1,24 @@
+public class P23 {
+    private String parentVariable = "Parent";
+
+    public void parentMethod() {
+        System.out.println("Parent method");
+        Child child = new Child();
+        child.childMethod();
+    }
+
+    public class Child {
+        private String childVariable = "Child";
+
+        public void childMethod() {
+            System.out.println("Child method");
+            System.out.println("Accessing parent variable: " + parentVariable);
+            System.out.println("Accessing child variable: " + childVariable);
+        }
+    }
+
+    public static void main(String[] args) {
+        P23 parent = new P23();
+        parent.parentMethod();
+    }
+}

P25.java

@@ -0,0 +1,25 @@
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class P25 {
+    public static void main(String[] args) {
+        List<String> names = new ArrayList<>();
+        
+        names.add("Batu");
+        names.add("Amba");
+        names.add("John");
+        names.add("Quandangle");
+        names.add("Harikrishan");
+        
+        System.out.println("Names before sorting:");
+        for (String name : names)
+            System.out.print(name + " ");
+        
+        Collections.sort(names);
+        
+        System.out.println("\nNames after sorting:");
+        for (String name : names)
+            System.out.print(name + " ");
+    }
+}