Generics

.gitignore

@@ -1,2 +1,3 @@
 *.iml
 .idea/
+out/

src/Generics/GenericExercise1.java

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+package Generics;
+
+public class GenericExercise1 {
+    public static void main(String[] args) {
+        //  Change elements in Integer array
+        Integer[] arr = new Integer[]{ 1, 2 };
+
+        System.out.println("------ Test Integer array ------");
+        printArr(arr);
+        Changer.change(arr);
+        printArr(arr);
+        System.out.println();
+
+        // Change elements in String array
+        String[] arr2 = new String[]{ "Hello", "world" };
+
+        System.out.println("------ Test String array ------`");
+        printArr(arr2);
+        Changer.change(arr2);
+        printArr(arr2);
+
+    }
+
+    public static <T> void printArr(T[] arr) {
+        for (T a: arr) {
+            System.out.print(a + " ");
+        }
+        System.out.println();
+    }
+}
+
+class Changer {
+    static <T> void change(T[] arr) {
+        T temp = arr[0];
+        arr[0] = arr[1];
+        arr[1] = temp;
+    }
+}

src/Generics/GenericExercise2.java

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+package Generics;
+
+import java.util.ArrayList;
+
+public class GenericExercise2 {
+    public static void main(String[] args) {
+        //  Test Integer array
+        System.out.println("------ Test Integer array ------");
+        Integer[] arr = { 1, 2, 3, 4 };
+        ArrayList<Integer> arrayList;
+
+        arrayList = toArrayList(arr);
+        printArrayList(arrayList);
+        System.out.println();
+
+        //  Test String array
+        System.out.println("------ Test String array ------");
+        String[] strArr = { "Hello", "world", "!!!"};
+        ArrayList<String> stringArrayList;
+
+        stringArrayList = toArrayList(strArr);
+        printArrayList(stringArrayList);
+    }
+
+    static <T> ArrayList<T> toArrayList(T[] arr) {
+        ArrayList<T> arrayList = new ArrayList<>();
+
+        for (T e: arr) {
+            arrayList.add(e);
+        }
+
+        return arrayList;
+    }
+
+    static <T> void printArrayList(ArrayList<T> arrayList) {
+        for(T e: arrayList) {
+            System.out.print(e + " ");
+        }
+
+        System.out.println();
+    }
+}

src/Generics/GenericExercise3.java

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+package Generics;
+
+import java.util.ArrayList;
+
+public class GenericExercise3 {
+    public static void main(String[] args) {
+        Box<Orange> b1, b3;
+        Box<Apple> b2;
+
+        b1 = new Box<>();
+        b2 = new Box<>();
+        b3 = new Box<>();
+        for (int i = 0; i < 10; i++) {
+            b1.addFruit(new Orange());
+        }
+        for (int i = 0; i < 10; i++) {
+            b2.addFruit(new Apple());
+        }
+        for (int i = 0; i < 10; i++) {
+            b3.addFruit(new Orange());
+        }
+
+        System.out.println("box1: weight: " + b1.getWeight());
+        System.out.println("box2: weight: " + b2.getWeight());
+        System.out.println("box3: weight: " + b3.getWeight());
+        System.out.println();
+
+        //  Compare test
+        System.out.println("------ Compare test ------");
+        System.out.println("b1 == b2: " + b1.compareTo(b2));
+        System.out.println("empty(Orange) == empty(Apple): " + new Box<Orange>()
+                .compareTo(new Box<Apple>()));
+        System.out.println("b1 == b3: " + b1.compareTo(b3));
+        System.out.println();
+
+        //  Drop test
+        System.out.println("------ Drop test ------");
+        b1.dropFruits(b3);
+        System.out.println("b3: weight: " + b3.getWeight());
+        System.out.println("b1: weight: " + b1.getWeight());
+    }
+}
+
+abstract class Fruit {
+    abstract public float getWeight();
+}
+
+class Apple extends Fruit {
+
+    @Override
+    public float getWeight() {
+        return 1.0f;
+    }
+}
+
+class Orange extends Fruit {
+
+    @Override
+    public float getWeight() {
+        return 1.5f;
+    }
+}
+
+class Box <T extends Fruit> {
+
+    ArrayList<T> fruits;
+
+    public Box() {
+        fruits = new ArrayList<>();
+    }
+
+    public void addFruit(T fruit) {
+        fruits.add(fruit);
+    }
+
+    public float getWeight() {
+        float weight = 0.0f;
+
+        if (fruits.size() > 0) {
+            weight = fruits.size() * fruits.get(0).getWeight();
+        }
+
+        return weight;
+    }
+
+    public boolean compareTo(Box<?> box) {
+        return (getWeight() == box.getWeight());
+    }
+
+    public void dropFruits(Box<T> box) {
+        while (fruits.size() > 0) {
+            box.addFruit(fruits.remove(0));
+        }
+    }
+}