In the program, a 'generic interface class' 'Swapper' is defined.

Write a class 'StringSwapper' that implements this interface and 
binds the generic type to a 'string' (i.e., the StringSwapper class is not generically defined).

An object created from StringSwapper works in such a way that it always holds only one string value at a time.
The class should have:
A constructor that receives a string as a parameter.
An implementation of the swapValue method: the method returns the current value of the swapper and saves the new value passed as a parameter in its place.




Example of using the class:
public static void main(String[] args) {
    StringSwapper swapper = new StringSwapper("hello");
    
    System.out.println(swapper.swapValue("hi there"));
    System.out.println(swapper.swapValue("greetings"));
    System.out.println(swapper.swapValue("good day now"));
}

The program prints:
hello
hi there
greetings




===============================================================


import java.util.Random;

public class Test {
    public static void main(String[] args) {
        final Random r = new Random();
        
        System.out.println("Testing the StringSwapper class...");
        
        String[] queues = "fox wolf pig mouse duck cow".split(" ");
        String[] q2 = "hamster guinea pig gerbil giraffe elephant".split(" ");
        
        String value = q2[r.nextInt(q2.length)];
        System.out.println("Creating object with parameter " + value);
        
        
        Swapper<String> swapper = new StringSwapper(value);
        System.out.println("Object created!");
        
        for (String queue : queues) {
            System.out.println("Switching value to " + queue);
            value = swapper.swapValue(queue);
            System.out.println("Object returned previous value " + value);
        }
    }
}


interface Swapper<T> {
    T swapValue(T value);
}


//ADD
class StringSwapper implements Swapper<String> {
    private String value;
    
    // constructor
    public StringSwapper(String value) {
        this.value = value;
    }

    @Override
    public String swapValue(String value) {
        // retrieve old value
        String oldValue = this.value;

        // update value
        this.value = value;

        // return/pop old value
        return oldValue;
    }
}



Testing the StringSwapper class...
Creating object with parameter elephant
Object created!
Switching value to fox
Object returned previous value elephant
Switching value to wolf
Object returned previous value fox
Switching value to pig
Object returned previous value wolf
Switching value to mouse
Object returned previous value pig
Switching value to duck
Object returned previous value mouse
Switching value to cow
Object returned previous value duck