为什么我不能在这个循环中调用另一个类的方法？

Question

I'm trying to make a filter in the Catalogue class that will later print out 'parts' that have a price greater than the minimum price that the user has entered. However I am not able to call getNumPrice() (which is in the Part class) from the Catalogue class and I am not sure why? How can I fix this and what am I doing wrong?

   //The following is in the Part class

 public double getNumPrice(){
        return this.price;
    }

//The following is in the Catalogue class

 private double readMinPrice(){
        System.out.println("Enter minimum price ('-1' for no filtering): ");
        return In.nextDouble();
    }

 private void filter(){
        String type =readTypeFilter();
        double minPrice = readMinPrice();

       if ( type== "all" && minPrice==-1)
            showParts();
        else if (type=="all" && minPrice >= 0)

            for(int i=0; i<= parts.size();i++)
                if (part.getNumPrice() >= minPrice)
                    System.out.println( i+1 + "." +  parts.get(i));
}

Answer 1

You have a parts collection and you are calling part.getNumPrice() in your loop.

I don't see either declared in your code but I'm assuming parts is a field and you are trying to do something like parts.get(i).getNumPrice() in the loop.

Answer 2

You need to use the indexed part in your loop.

for(int i=0; i<= parts.size();i++)
   if (parts.get(i).getNumPrice() >= minPrice)