Implement the class method public static void swap(Stack xs, Stack ys). The method exchanges the content of two stacks, xs and ys. The method must work for any valid implementation of the interface Stack; You can assume the existence of the classes DynamicArrayStack and LinkedStack. Stack a, b; a = new LinkedStack (); a.push("alpha"); a.push("beta"); a.push("gamma"); b = new DynamicArrayStack(); b.push("blue"); b.push("green"); b.push("yellow"); b.push("black"); System.out.println(a); System.out.println(b); swap (a, b); System.out.println(a); System.out.println(b); In particular, the above statements should print the following. [gamma, beta, alpha] [black, yellow, green, blue] [black, yellow, green, blue] [gamma, beta, alpha] public static void swap(Stack xs, Stack ys) {