Question

17. For this problem you must define a simple generic interface PairInterface, and two implementations of the interface, BasicPair and ArrayPair.

a. Define a Java interface named PairInterface. A class that implements this interface allows creation of an object that holds a “pair” of objects of a specified type—these are referred to as the “first” object and the “second” object
of the pair. We assume that classes implementing PairInterface provide constructors that accept as arguments the values of the pair of objects. The PairInterface interface should require both setters and getters for the first and second objects. The actual type of the objects in the pair is specified when the PairInterface object is instantiated. Therefore, both the PairInter- face interface and the classes that implement it should be generic. Suppose a class named BasicPair implements the PairInterface interface. A simple sample application that uses BasicPair is shown here. It's output would be "apple orange."

public class Sample {

public static void main (String[] args) {

PairInterface myPair<String> =
new BasicPair<String>("apple", "peach");

System.out.print(myPair.getFirst() + " ");

myPair.setSecond("orange");

System.out.println(myPair.getSecond()); }

}

b. Create a class called ArrayPair that implements the PairInterface inter- 10 face.

- This class should use an array of size 2 to represent the two objects of the pair.

- Create a test driver application that demonstrates that the ArrayPair class works correctly.

Answer 1

PairInterface.java

public interface PairInterface<T> {
   // declare abstract methods
   public void setFirst(T first);
   public void setSecond(T second);
   public T getFirst();
   public T getSecond();
}

BasicPair.java

// implement PairInterface interface
public class BasicPair<T> implements PairInterface<T> {
   // instance variables
   private T first;
   private T second;
   // constructor
   public BasicPair(T first, T second) {
       super();
       this.first = first;
       this.second = second;
   }
   // setters and getters
   @Override
   public T getFirst() {
       return first;
   }
   @Override
   public void setFirst(T first) {
       this.first = first;
   }
   @Override
   public T getSecond() {
       return second;
   }
   @Override
   public void setSecond(T second) {
       this.second = second;
   }
}

ArrayPair.java

// implement PairInterface interface
public class ArrayPair<T> implements PairInterface<T> {
   // instance variable
   private T array[];
   // constructor
   public ArrayPair(T[] array) {
       super();
       this.array = array;
   }
   // setters and getters
   @Override
   public void setFirst(T first) {
       array[0]=first;
   }
   @Override
   public void setSecond(T second) {
       array[1]=second;
   }
   @Override
   public T getFirst() {
       return array[0];
   }
   @Override
   public T getSecond() {
       return array[1];
   }
}

Sample.java

public class Sample {
   public static void main(String[] args) {
       System.out.println("BasicPair class: ");
       // create BasicPair class object with generic type String
       PairInterface<String> myPair =new BasicPair<>("apple", "peach");
       System.out.print(myPair.getFirst() + " "); // get first
       myPair.setSecond("orange"); // set second
       System.out.println(myPair.getSecond()); // get second
      
       System.out.println("\nArrayPair class: ");
       // create 2 size array
       String array[]= {"apple","peach"};
       // create ArrayPair class object with generic type String
       PairInterface<String> myPair2=new ArrayPair<>(array);
       System.out.print(myPair2.getFirst() + " ");
       myPair2.setSecond("orange");
       System.out.println(myPair2.getSecond());
   }
}

Output