Java pitfall - 破坏封装性

public class Father {

    private double property=90;
   
    /**
     * @param args
     */
    public static void main(String[] args) {
        Father son = new Son();
        System.out.println("My father's property is = "+son.property++);
        System.out.println("My father's property is = "+son.property);
    }
   
}

class Son extends Father{
   
    public double property;

    public void addProperty(double fund){
        property += fund;
    }
}