Well it just showing till wave - 2 and then the 'wave - 2' statement stays through out the screen.
Can u help me in one more thing that there should be a delay after each wave destroyed i mean the world should keep on running and after some time delay the next wave appear on screen.
As an added bonus, the Text class is not restricted to creating an object that only displays 'wave' text (you can use it to create multiple text objects dealing with any text). It can also be modified slightly to allow for different background colors, text colors and different text size. Static fields can be used to allow these differences when creating the objects; and instance fields with get and set methods can be used to allow changing these states after the objects were already created.
I was just saying that with the Text class as I have given it, you can use it for, let us say:
(1) a wave text object
(2) a score object
(3) a message object
(4) a highscore object
all at the same time.
My 'Pong Pinball' scenario has a Text class that is used twice in the Arena world class and twice more in the Paddle class to create four different Text objects. Download it and review the code to see how it works.