Java OCA OCP Practice Question 2312

Question

What will be the result of attempting to compile the following code? 

 class Vehicle { }
 class Car extends Vehicle { }
 class Sedan extends Car { }

 class Garage<V> {
   private V v;/*from  ww  w  . ja  v a  2  s  .  c  o m*/
   public V get() { return this.v; }
   public void put(V v) { this.v = v; }
}

public class Main {

  private Object object = new Object();
  private Vehicle vehicle = new Vehicle();
  private Car car = new Car();
  private Sedan sedan = new Sedan();

  public void doB(Garage<Car> g) {
    g.put(object);            // (1)
    g.put(vehicle);           // (2)
    g.put(car);               // (3)
    g.put(sedan);             // (4)
    object  = g.get();        // (5)
    vehicle = g.get();        // (6)
    car     = g.get();        // (7)
    sedan   = g.get();        // (8)
  }
}

Select the two correct answers.

  • (a) The call to the put() method in statements (1) - (2) will compile.
  • (b) The call to the put() method in statements (3) - (4) will compile.
  • (c) The assignment statements (5), (6) and (7) will compile.
  • (d) The assignment statement (8) will compile.


(b) and (c)

Note

The type of reference g is of Garage<Car>.

We can put a Car in such a garage and get a Car out.

The type of value returned by the get() method in statement (8) is Car and, therefore, not compatible for assignment to Sedan.




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