how about "instance initializer block" ?

[athinboy]

there is a feature "instance initializer block" in java:
https://www.javatpoint.com/instance-initializer-block

class Box{
  public int level;
  public int length;
  public int width;
  public int height;

 
  public Box(int length,int width,int height){
     this.length=length;
     this.width=width;
     this.height=height;
     
  }
  //-----some other contructors

  //-------------------------------
  
}

class SmallBox:Box{
  {
    this.level=1;
  }
}

class MiddleBox:Box{
  {
    this.level=1;
  }
}

class BigBox:Box{
  {
    this.level=1;
  }
}

[huoyaoyuan]

I believe most of the usage can be covered by member initializer. Other of them can be a private constructor called by others.