initial commit

core-banking/src/com/example/banking/application/StudyPolymorphism.java

@@ -6,6 +6,7 @@
 import com.example.banking.domain.Account;
 import com.example.banking.domain.CheckingAccount;
 
+@SuppressWarnings("unused")
 public class StudyPolymorphism {
 
 	public static void main(String[] args) {

study-primitive-types/src/com/example/StudyWrapperClasses.java

@@ -2,6 +2,7 @@
 
 import java.util.List;
 
+@SuppressWarnings("unused")
 public class StudyWrapperClasses {
 
 	public static void main(String[] args) {

zoo/src/com/example/zoo/application/ZooApp.java

@@ -0,0 +1,64 @@
+package com.example.zoo.application;
+
+import static java.util.stream.Collectors.counting;
+import static java.util.stream.Collectors.groupingBy;
+
+import java.util.List;
+
+import com.example.zoo.domain.Animal;
+import com.example.zoo.domain.Cat;
+import com.example.zoo.domain.Fish;
+import com.example.zoo.domain.Pet;
+import com.example.zoo.domain.Spider;
+
+public class ZooApp {
+
+	public static void main(String[] args) {
+		var zoo = List.of(
+		    new Spider(),
+		    new Cat(),
+		    new Fish("Free Willy"),
+		    new Spider(),
+		    new Cat("Garfield"),
+		    new Fish("Nemo"),
+		    new Spider(),
+		    new Cat()
+		);
+
+		for (var animal : zoo) {
+			animal.walk();
+			animal.eat();
+			if (animal instanceof Pet pet) {
+				// var pet = (Pet) animal;
+				pet.play();
+			}
+		}
+		// outer loop
+		var totalLegs = 0;
+		for (var animal : zoo) {
+			if (animal instanceof Pet) {
+				totalLegs += animal.getLegs(); 
+			}
+		}	
+		System.out.println("Total number of legs: %d".formatted(totalLegs));
+
+		// Since Java SE 8: Functional Programming
+		totalLegs =
+		zoo.stream() // inner loop
+		   //.filter( animal -> animal instanceof Pet)
+		   //.filter( animal -> Pet.class.isInstance(animal) )
+		   .filter( Pet.class::isInstance )
+		   //.mapToInt( animal -> animal.getLegs())
+		   .mapToInt(Animal::getLegs)
+		   .sum();
+		// one-liner
+		totalLegs = zoo.stream().parallel().filter(Pet.class::isInstance).mapToInt(Animal::getLegs).sum();
+		System.out.println("Total number of legs: %d".formatted(totalLegs));
+
+		// Stream API + Functional Programming + Filter/Map/Reduce
+		zoo.stream()
+		   .collect(groupingBy(Animal::getClass,counting()))
+		   .forEach((clazz,count) -> System.out.println("%s: %d".formatted(clazz.getSimpleName(),count))) ;
+	}
+
+}