检查ArrayList中包含的对象中是否存在某个字符串，然后将该对象添加到另一个ArrayList中

Question

I have Arraylist of objects ArrayList<Product> productDatabase. The object contains a String and a double and then these objects will be added to the productDatabase by addProductToDatabase(); as follows:

public void addProductToDatabase(String productName, double dimensions); {
    Product newProduct = new Product(ProductName, dimensions);
    productDatabase.add(newProduct);
}

I also want to make an Arraylist<ProductCount> productInventory which counts how many Product are accounted for. Before it can add to ArrayList<ProductCount> productInventory however, it should first check if the object details exist in the productDatabase while running addProductToInventory()

public Product getProduct(String name) {
    for(i = 0; i < productDatabase.size(); i++)
    if(productDatabase.get(i).contains(name) //Error: cannot find symbol- method contains.(java.lang.String)
        return productDatabase.get(i)
}

public void addProductToInventory(String productName, double quantity)
{
    Product p = getProduct(name);        
    productCount.add(new ProductCount(o, quantity)); 
}

Assume that you always have different objects (so nothing will have the same name), but you're always unsure of the dimensions (so when you input the same producttName + dimensions you edit the dimensions in it).

At the end of the day, you have to put all the items in it a large box and report what you've inventoried, so you also have a getProductQuantityTotal() and you have to getProductDimensionTotal() -- as the name suggests, get the total of number of objects you've counted, and the sum of the dimensions.

What do I have to add/change/remove about this code? Don't consider syntax first (because BlueJ checks for common syntax errors and I just typed this by hand). I'm sure that I'm missing a for statement somewhere, and I'm probably misusing contains() because it won't recognise it (I have import java.util.*; and import java.util.ArrayList; )

Answer 1

To answer the question in your post title: How to find a string in an object , for a list of those objects, here is some sample code that does this:

First, I created a trivial object that has a string field:

class ObjectWithStringField  {
   private final String s;
   public ObjectWithStringField(String s)  {
      this.s = s;
   }
   public String getString()  {
      return  s;
   }
}

And then a code that populates a list of it, and then searches each for the string. There's no magic here, it just iterates through the list until a match is found.

import  java.util.List;
import  java.util.Arrays;

/**
   <P>{@code java StringInObjectInList}</P>
 **/
public class StringInObjectInList  {
   public static final void main(String[] ignored)  {
      ObjectWithStringField[] owStrArr = new ObjectWithStringField[]  {
         new ObjectWithStringField("abc"),
         new ObjectWithStringField("def"),
         new ObjectWithStringField("ghi")};

      //Yes this is a List instead of an ArrayList, but you can easily 
      //change this to work with an ArrayList. I'll leave that to you  :)
      List<ObjectWithStringField> objWStrList = Arrays.asList(owStrArr);

      System.out.println("abc? " + doesStringInObjExistInList("abc", objWStrList));
      System.out.println("abcd? " + doesStringInObjExistInList("abcd", objWStrList));
   }
   private static final boolean doesStringInObjExistInList(String str_toFind, List<ObjectWithStringField> owStrList_toSearch)  {
      for(ObjectWithStringField owStr : owStrList_toSearch)  {
         if(owStr.getString().equals(str_toFind))  {
            return  true;
         }
      }
      return  false;
   }
}

Output:

[C:\java_code\]java StringInObjectInList
abc? true
abcd? false

In the real world, instead of a List , I'd use a Map<String,ObjectWithStringField> , where the key is that field. Then it'd be as simple as themap.containsKey("abc"); . But here it is implemented as you require. You'll still have quite a bit of work to do, to get this working as specifically required by your assignment, but it should get you off to a good start. Good luck!