SubClass1 subClassVar1 = (SubClass1) superClassVar1;

Week 6: Methods of OO Programming/11B. Calculate the Total Load of Trucks

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+In the program, a class Car and its subclass Truck are defined.
+
+Write a method
+public static int totalLoad(ArrayList<Car> cars)
+
+that receives a list of Truck objects as a parameter. 
+The method calculates and returns the total load of the trucks.
+Note that the list type is Car, not Truck!
+
+
+
+import java.util.Random;
+import java.util.ArrayList;
+
+public class Test{
+    public static void main(String[] args){
+        final Random r = new Random();
+        
+        String[] brands = "Sisu Scania Volvo Ford Fiat Citroen".split(" ");
+        
+        for(int test=1; test<=3; test++) {
+            
+            System.out.println("Test " + test);
+        
+            ArrayList<Car> cars = new ArrayList<>();
+            
+            final int size = r.nextInt(4) + 3;
+            for (int i=0; i<size; i++) {
+                cars.add(new Truck(brands[r.nextInt(brands.length)], r.nextInt(20) + 5));
+            }
+            System.out.println("Cars:");
+            cars.stream().forEach(a -> System.out.println("" + a));
+            
+            System.out.println("Total load: " + totalLoad(cars));
+            System.out.println("");
+    
+        }
+    }
+
+
+
+    //add
+    // round 1 - NO
+    // public static int totalLoad(ArrayList<Car> cars) {
+    //     int totalLoad = 0;
+    //     for (Truck truck : cars) {
+    //         totalLoad += truck.getLoad();
+    //     }
+    //     return totalLoad;
+    // }
+
+
+    // round 2 - YES
+    public static int totalLoad(ArrayList<Car> cars) {
+        int totalLoad = 0;
+        for (Car car : cars) {
+            // explicit type casting
+            Truck truck = (Truck) car;
+            totalLoad += truck.getLoad();
+        }
+        return totalLoad;
+    }
+
+
+
+
+}
+
+
+
+
+
+class Car {
+    protected String brand;
+    
+    public Car(String brand) {
+        this.brand = brand;
+    }
+
+    public String getBrand() {
+        return brand;
+    }
+}
+
+class Truck extends Car {
+    private int load;
+
+    public Truck(String brand, int load) {
+        super(brand);
+        this.load = load;
+    }
+    
+    public int getLoad() {
+        return load;
+    }
+    
+    public String toString() {
+        return brand + ", load: " + load;
+    }
+}
+
+
+
+
+
+
+
+
+
+
+
+Test 1
+Cars:
+Sisu, load: 5
+Volvo, load: 24
+Sisu, load: 23
+Total load: 52
+
+Test 2
+Cars:
+Fiat, load: 9
+Fiat, load: 10
+Scania, load: 13
+Ford, load: 16
+Total load: 48
+
+Test 3
+Cars:
+Volvo, load: 18
+Ford, load: 22
+Scania, load: 20
+Sisu, load: 20
+Volvo, load: 7
+Sisu, load: 21
+Total load: 108
+
+