参考：https://www.cnblogs.com/dolphin0520/p/3803432.html

1.初始化

2.构造函数

3.单类的执行顺序，先1后2；

4.继承：先父类，再子类。

5.成员变量，成员方法，都只继承public,protected的，private不继承。

6.static和final方法，不能继承和覆盖。成员变量，同理。

public class Test {
    public static void main(String[] args)  {
        new Circle();
    }
}

class Draw {

    public Draw(String type) {
        System.out.println(type+" draw constructor");
    }
}

class Shape {
    private Draw draw = new Draw("shape");

    public Shape(){
        System.out.println("shape constructor");
    }
}

class Circle extends Shape {
    private Draw draw = new Draw("circle");
    public Circle() {
        System.out.println("circle constructor");
    }
}

输出：

shape draw constructor
shape constructor
circle draw constructor
circle constructor