key point

子类构造函数

public class Father {
 
     public void draw() {
         System.out.println("father draw");
     }
     
     public Father() {
         System.out.println("father:before draw");
         draw();
         System.out.println("father:after draw");
     }
 
 }

public class Son extends Father {
 
     private int number = 1;
     
     public Son(int number) {
         this.number = number;
         System.out.println("init number:" + this.number);
     }
     
     @Override
     public void draw() {
         System.out.println("son draw number:" + this.number);
     }
 }

public class MainTest <T> extends Object{
    
    public static void main(String[] args) {
        new Son(5);
    }
}

输出结果
father:before draw
son draw number:0
father:after draw
init number:5

子类构造函数的第一行都是super(); 如果没有super()的话 编译器自动增加super.
基类的构造函数调用draw. 因为virtureinvoke 的关系 会调用子类的draw
子类的number 没有被初始化完成. 只有默认的0
完成基类的构造, 回到子类
完成构造