class calc{
    public static void main(String argv[]){
	calculate me = new recalculate();
	me.setA(1);
	me.divide();
    }	
}

class calculate{
    protected int a =1;
    protected void setA( int i ){ if(i>0) a=i; }
    public void divide(){ float f = 7 / a; }
}

class recalculate extends calculate {
    public void setA(int i){ a=i; }
}