在Java中过滤项目

Question

I have a package, called Things. In this package, there are regular and abstract classes such as Fruit, Food, Perishable, Shoes, Item etc. I want to create a filter that would filter these when clicked on. For example, clicking on the button fruit would filer for fruits. In a separate package called CODE, I have 4 classes, each serving a function such as importing my data and methods, running the app, the GUI and the controller. I've set up the GUI class to show the button, however, I am confused on how to get Java to filter my items in the "listening" class - a class which responds to the buttons clicked in the GUI class. How do I approach writing the code? I have tried the following, but it doesn't work. Do I have to import things.food in the code?

In another post there was this code:

List<Person> beerDrinkers = persons.stream()
.filter(p -> p.getAge() > 16).collect(Collectors.toList());

//Lets say I edit this to make it similar to my problem
List<Item> Perishables = Food.stream()
.filter(p -> p.getName()).collect(Collectors.toList());

That would not work, and it gives me errors. Could someone explain how this code works and how I could apply it to my problem?

// I currently have this empty in my controller class to use as a filter. Am I suppose to filter over here or in the class that holds the methods?
else if(text.equals("Food")){
    }

package Products; public abstract class Food extends Item {

String Expiration_Date;

public String toString()
{
    return super.toString() + ", Expiration: " + Expiration_Date;
}
}

package Products;

public class Fruit extends Perishable {

public Fruit(String s)
{
    StringTokenizer stk = new StringTokenizer(s);

    stk.nextToken();

    this.Item_name = stk.nextToken();
    this.Item_code = stk.nextToken();
    this.price = Double.parseDouble(stk.nextToken());
    this.Expiration_Date = stk.nextToken();
    if (stk.nextToken().compareTo("false") == 0)
        this.flag = false;
    else
        this.flag = true;
    this.inventory = Integer.parseInt(stk.nextToken());

}

public String toString()
{
    return super.toString();
}

}

Answer 1

The code that you referred to is using JDK 1.8. You should check your jdk version by executing javac -version in the console.

List<Item> foods = perishables.stream()
.filter(p -> p.getSimpleName().equals("Food")).collect(Collectors.toList());

Referring to the source, Food is a list for Item? List.stream() returns Stream interface with the collection. Stream is a interface of JDK 1.8 that we can create a closure to operate the collection element. You should return a bool value in the filter method.

stream() is a method of class that implements Collection , so we use this method of an ArrayList(or others) of Perishable to get Stream interface with Perishable objects. Then use filter method to filter Perishable objects and return a new stream with filtered objects. Finally using collect(Collectors.toList()) to accumulate filtered objects to an ArrayList.

BTW Class.getSimpleName can return a short class name without package names.