Assume the existence of a Window class with integer instance variables width, height, xPos and yPos. Define the method toString for the Window class. The String representation of a Window object should be of the form "A 'width'x'height' window at ('xPos','yPos')" where the values within the apostrophes are replaced by the actual values of the corresponding instance variables. For example, given a Window object whose width is 80, height is 20, xPos is 0 and yPos is 30, toString should return "A 80x20 window at (0,30)."