package chapter4;

class MostCommonDiv{
    private int m;
    private int n;
    
    public int f(int a, int b){
        this.m = a;
        this.n = b;
        
        if(m<n){
            int temp = 0;
            temp = m;
            m = n;
            n = temp;
        }
        
        int start = n;
        int div = 0;
        for(int i=start; i>0; i--){
            if((m%i == 0) && (n%i == 0)){
                div = i;
                break;
            }
        }
        return div;
    }
}

class SubMostCommonDiv extends MostCommonDiv{
    
    protected static int resultOfSupper = 0;
    
    public int f(int a, int b){
        int m = super.f(a, b);
        this.resultOfSupper = (a*b)/m;
        
        if(a<b){
            int temp = 0;
            temp = a;
            a = b;
            b = temp;
        }
        
        int start = a;
        int subdiv = 0;
        while(start > 0){
            if((start%a == 0) && (start%b ==0)){
                subdiv = start;
                break;
            }else{
                start ++;
            }
        }
        
        return subdiv;
    }
}


public class Exam4_18 {

    public static void main(String[] args) {
        MostCommonDiv test1 = new MostCommonDiv();
        SubMostCommonDiv test2 = new SubMostCommonDiv();
        int a = 32;
        int b = 8;
    
        System.out.println("f function in father:"+test1.f(a, b));
        System.out.println("f function in son:"+((SubMostCommonDiv)test1).f(a, b));
        System.out.println("add the result of (a*b)/m="+SubMostCommonDiv.resultOfSupper);
        
        System.out.println("f function in son:"+test2.f(a, b));
        System.out.println("add the result of (a*b)/m="+test2.resultOfSupper);
    
    }

}

public class Exam4_18 {

    public static void main(String[] args) {
        MostCommonDiv test1 = new SubMostCommonDiv();
        SubMostCommonDiv test2 = new SubMostCommonDiv();
        int a = 32;
        int b = 8;
    
        System.out.println("f function in father:"+test1.f(a, b));
        System.out.println("f function in son:"+((SubMostCommonDiv)test1).f(a, b));
        System.out.println("add the result of (a*b)/m="+SubMostCommonDiv.resultOfSupper);
        
        System.out.println("f function in son:"+test2.f(a, b));
        System.out.println("add the result of (a*b)/m="+test2.resultOfSupper);
    
    }

}

------解决方案--------------------
MostCommonDiv test1 = new MostCommonDiv();
  test1 声明的是父类, 实现的是父类, 这样是不能强转成子类的.

只有多态的方式下,才能向下转型呢.  
比如:
MostCommonDiv test3=new SubMostCommonDiv();
这样可以用(SubMostCommonDiv)test3.

(但多态的情况下,自然调用的方法是子类覆写了的父类方法. 也不需要转型了.
只有调用子类新加的方法,才需要用向下转型后去调用.)

------解决方案--------------------
System.out.println("f function in son:"+((SubMostCommonDiv)test1).f(a, b));

错误很明显，父类对象不能强转成子类的