P1-P5: rewrite to match current syllabus

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

P3.java

@@ -1,14 +1,27 @@
-class P3 {
-  public static void main(String[] _args) {
-      int a = 5, b = -5, c = 55, mx;
+interface Animal {
+    void makeSound();
+}
 
-      if (a > b && a > c)
-          mx = a;
-      else if ( b > a && b > c)
-          mx = b;
-      else
-          mx = c;
+class Cat implements Animal {
+    @Override
+    public void makeSound() {
+        System.out.println("Meow!");
+    }
+}
 
-      System.out.println("max(" + a + ", " + b + ", " + c + ") = " + mx);
-  }
-}
+class Cow implements Animal {
+    @Override
+    public void makeSound() {
+        System.out.println("Moo!");
+    }
+}
+
+public class P3 {
+    public static void main(String[] args) {
+        Animal cat = new Cat();
+        Animal cow = new Cow();
+        
+        cat.makeSound();
+        cow.makeSound();
+    }
+}