从存储在arraylist中的对象调用方法

Question

I was wondering why this isn't working. I looked at another post that suggested the method I used for calling methods from Objects stored in an array but it doesn't seem to be working. I should clarify. I am referring to the printPurchases and totalCost methods. More specifically how they don't seem to be allowing me to call from the Purchase object at index i , but instead appear to be calling from the get(i) part. It is highlighted in red in my eclipse application.

public class Customer {

    private String name, address;
    double total;
    private ArrayList purchases = new ArrayList();

    public Customer(String name, String address){
        this.address=address;
        this.name=name;
    }

    public void makePurchase(Purchase purchase){
        purchases.add(purchase);
    }

    public String printPurchases(){
        for(int i=0; i<purchases.size(); i++){
            return **name+"\t"+address+purchases.get(i).toString();**
        }
        return"";
    }

    public double totalCost(){
        total=0;
        for(int i=0; i<purchases.size(); i++){
            total = **total+purchases.get(i).getCost();**
        }
    }
}

Answer 1

Your return statement should have a space in between return and "" .

public String printPurchases(){
    for(int i=0; i<purchases.size(); i++){
        return name+"\t"+address+purchases.get(i).toString();
    }
    return "";
}

public double totalCost() is suppose to return a double . You aren't returning a double .

public double totalCost(){
    total=0;
    for(int i=0; i<purchases.size(); i++){
        total = total+purchases.get(i).getCost();
    }

    return total;
}

Also, as said in the comments, specify what the ArrayList is to be filled with, by using:

private ArrayList<Purchase> = new ArrayList<Purchase>();

Answer 2

当您将类型信息（即Purchase属性和方法）存储在没有泛型的ArrayList时，其类型信息（即Purchase的属性和方法）将被删除（上载至Object ，没有自定义的属性或方法），请尝试按以下方式存储它们：

private ArrayList<Purchase> purchases = new ArrayList<>();