📦 NEW: add AbstractFinal.java as provided in exercice

Signed-off-by: Jonas Sulzer <jonas@violoncello.ch>

src/Ex_05/AbstractFinal.java

+package Ex_05;
+
+class AbstractFinal {
+    public static void main(String[] args) {
+
+        A[] tab = new A[3];
+
+        tab[0] = new A();
+        tab[1] = new B();
+        tab[2] = new C();
+
+        tab[1].b = 2;
+        ((C)tab[2]).c = 3;
+    }
+}
+
+abstract class A {
+    int a;
+}
+
+class B extends A {
+    int b;
+}
+
+class C extends A {
+    final double c = 1;
+}
+
+abstract class D extends A {
+    double d;
+
+    int operation(int a) {
+        return (a * 2);
+    }
+
+    abstract int calcul(int b) {
+
+    }
+
+    abstract int machin();
+}
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