extras: add P16-P23, P25

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

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();
+    }
+}