Getter from another class doesn't work on ArrayList

Question

so I've been scratching over why my code doesn't work. I have 2 classes, the first one is where I have my getters and setters:

public class ShopItems {
  private String itemName;
  private double price;

  public double getPrice(){
    return price;
  }

  public String getItemName(){
    return itemName;
  }

  private void setPrice(p){
    price = Math.abs(p);
  }

  public ShopItems(String i, double p){
    itemName = i.toUpperCase();
    setPrice(p);
  }
}

and here is my second class, where I make an ArrayList:

public class ShopLedger {
  private ArrayList<ShopItems> shoppingList;

  //I want to make a deep copy of the items in the parameter into shopping list.
  public ShopLedger(ArrayList<ShopItems> s){
    shoppingList = new ArrayList<ShopItems> (s);

    for(int i=0;i<s.size();i++){
      shoppingList.set(i,s.get(i));
    }
  }

  //And here is where things go wrong. I want the method to return the price of the item
  //in the parameter, and return null if the item name cannot be found.
  public Double getPrice(String itemName) {
  for(int i=0;i<shoppingList.size();i++){
    if(shoppingList.get(i).getItemName() == itemName){
      return shoppingList.get(i).getPrice();
    }
  }
  return null;
 }
}

This is what I have now, and the code keeps giving me the error "java.lang.NullPointerException". My client class sets the shoppingList as: Candy(2.3), Book(20.0), Pens(5.5), Tape(10.2) and itemName is Pens. However, I've gone into debug mode and for some reason, this part of the getPrice method:

if(shoppingList.get(i).getItemName() == itemName){
      return shoppingList.get(i).getPrice();
}

never executes. Please help!

shoppingList.get(i).getItemName() == itemName here you should use equals — Hubert Bratek, May 14 '18 at 16:46
@Ajris if I try to do that, it gives me an error that says "the left hand side of an assignment must be a variable" — lettuce, May 14 '18 at 16:50
how do you use it? sth like that? shoppingList.get(i).getItemName().equals(itemName) — Hubert Bratek, May 14 '18 at 16:54
yeah like this: shopplingList.get(i).getItemName() = itemName — lettuce, May 14 '18 at 16:56
oh wow haha that was the only issue i had, it is fixed now. Thanks so much! — lettuce, May 14 '18 at 16:59
Please also note that while the comment on the `ShopLedger` constructor says that you want do make a deep copy of `s` there is no code making copies of the `ShopItems` — Thomas Kläger, May 14 '18 at 17:03

score 2 · Answer 1 · answered May 14 '18 at 17:02

2

I've found the issue, thanks to a user named Ajris, who pointed out that I should use shoppingList.get(i).getItemName().equals(itemName) in my if statement instead of shoppingList.get(i).getItemName() == itemName

answered May 14 '18 at 17:02

lettuce

67
7

score 1 · Accepted Answer · answered May 14 '18 at 17:03

1

You compare String with ==

Use equals(). "aaaa".equals("aaaa");

answered May 14 '18 at 17:03

KunLun

3,109
3
18
65

Yeah thank you! What a silly mistake hahaha – lettuce May 14 '18 at 17:07

score 0 · Answer 3 · answered May 14 '18 at 17:30

0

You might want to use the equals().

if(shoppingList.get(i).getItemName().equals(itemName){
      return shoppingList.get(i).getPrice();
}

answered May 14 '18 at 17:30

DK1446

3
2

you got your answer, anyway – DK1446 May 14 '18 at 17:31

Getter from another class doesn't work on ArrayList

3 Answers3