class StringSwapper implements Swapper<String> {...}

Week 7: Enum, Generic Type, Streams, write to file, class diagram/06B. Implement the StringSwapper Class

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+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
+
+
+