如何在方法中使用ArrayList作为参数从类的ArrayList中删除元素？

Question

My friend and I are studying for our programming exam doing the Sample Programming Exam, and are having trouble using an Array List as a parameter in a method to remove multiple items from an Array List in the same class.

We have tried searching the web and using our BlueJ textbook to find a solution.

The instruction on our assignment sheet says, "Write a method removeItemFromOrder with an array of strings itemArray parameter to remove multiple food items from the order."

import java.util.ArrayList;
/**
 * Write a description of class Order here.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class Order
{
    // instance variables - replace the example below with your own
    private ArrayList<OrderedItem> order;

    /**
     * Constructor for objects of class Order
     */
    public Order()
    {
        order = new ArrayList<>();
    }

    /**
     * Returns the order collection to the user.
     * @return the order collection.
     */
    public ArrayList getOrder()
    {
        return order;
    }

    /**
     * Add an item to the order.
     * @param OrderedItem the item to be added
     */
    public void addOrderItem(OrderedItem foodItem)
    {
        order.add(foodItem);
    }

    public void removeOrderItem(ArrayList<String> itemArray)
    {
        //**We don't know what to put here!**
    }
}

Answer 1

if you need to remove multiple items, you can add them to a temporary list and use removeAll too

// creating ArrayList 
java.util.List<String> list = new ArrayList<>();  
list.add("apple");
list.add("banana");
list.add("mango");
list.add("barry");

java.util.List<String> needToRemove = new ArrayList<>();
needToRemove.add("apple");
needToRemove.add("banana");

// removeAll will remove multiple elements,
// We can pass any collection like Set, List or any other
list.removeAll(needToRemove);        

System.out.println("After Removed From List:");
list.forEach(System.out::println);

Answer 2

Arraylist.clear(); method can be used to clear the array list Arraylist.removeAll(); method removes all the elements of the array list. Both the methods clear the elements of the list. The clear() method has a better performance due to the less number of lines it has to execute. This link https://howtodoinjava.com/java/collections/arraylist/empty-clear-arraylist/ provides the source codes for the two methods

Answer 3

很好的朋友，只要您有对象的密钥（即安全密钥.remove() ，就可以尝试使用.remove()方法

Answer 4

As I see the array list that you pass to removeOrderItem method is a list of strings and your array list in the class is a list of OrderItem . So first you must find what is common between these two lists.

Let's assume the model of OrderItem has a field that contains the name of each order ( orderItem.getName() ). And the itemArray in the removeOrderItem method is a list that contains names of some orders that you want to remove them.

Ok, in this case, we can do this:

public void removeOrderItem(ArrayList<String> itemArray) {
    List<OrderedItem> tempList = new ArrayList<>();

    for (OrderedItem food: this.order) {
        for (String foodName: itemArray) {
           if (food.getName().equals(foodName))
               tempList.add(food);
               break;
        }
    }

    this.order.removeAll(tempList);
}