定义4个类，MyShape、MyLine、MyRectangle和MyOval，其中MyShape是其他三个类的父类。MyShape为抽象类，包括图形位置的四个坐标；一个无参的构造方法，将所有的坐标设置为0；一个带参的构造函数，将所有的坐标设置为相应值；每个坐标的设置和读取方法；abstract void draw(Graphics g)方法。MyLine类负责画直线，实现父类的draw方法；MyRectangle负责画矩形，实现父类的draw方法；MyOval负责画椭圆，实现父类的draw方法。编写一个应用程序，使用上面定义的类，随机选取位置和形状，绘制20个图形。示例输出如图所示。-Define four classes, MyShape, MyLine, MyRectangle and MyOval, which is the other three MyShape parent class. MyShape is an abstract class, including the location of the four graphical coordinates　a no-argument constructor, all of the coordinates is set to 0　a parameterized constructor, all the coordinates to the corresponding value　coordinates of each set and read method　abstract void draw (Graphics g) method. MyLine class responsible for drawing straight lines, to achieve the parent class draw method　MyRectangle responsible for drawing a rectangle, the draw method to achieve the parent class　MyOval responsible for the ellipse, the draw method to achieve the parent class. Write an application using the class defined above, randomly selected location and shape, draw 20 graphics. Sample output as shown.