如何將新對象添加到ArrayList？

Question

我想添加一個新的對象到ArrayList。每個項目的對象將有3個屬性：

1. itemNum
2. 資訊
3. 成本

我也有3類：

1. 項目類定義存儲在單個項目目錄。
2. 目錄類維護着Item對象的列表。
3. 客戶類別w/main方法。

我有集合並獲取在Item類中，我在Catalog中有ArrayList。在客戶端中，我可以選擇添加，刪除或編輯對象。如何正確添加一個新的Item對象到ArrayList？

我得到Item類編譯好，但目錄和客戶端類不編譯。這是我與目錄類得到的錯誤：

Catalog.java:35: error: no suitable method found for add(int,String,double)listOfObjects.add(newItemId, newDescription, newCost); 
method ArrayList.add(int,Item) is not applicable 
(actual and formal argument lists differ in length) 
method ArrayList.add(Item) is not applicable 
(actual and formal argument lists differ in length) 

下面是項目類

Public class Item 
{ 
    private int itemNum; 
    private String info; 
    private double cost; 

    public Item() 
    { //start constructor 
    itemNum = 0; //default values 
    info = "x"; 
    cost = 0; 
    } //end constructor 

    public CatalogItem(int newItemNum, String newInfo, double newCost) 
    { //start overload constructor 
    this.itemNum = newItemNum; 
    this.info = newInfo; 
    this.cost = newCost; 
    } //end overload constructor 

下面

是一組代碼itemNum

/獲取

 public int getItemNum() 
    { //start itemNum accessor 
    return itemNum; 
    } //end getItemNum 

    public void setItemNum(int newItemNum) 
    { //start itemNum mutator 
    this.itemNum = newItemNum; 
    } //end setItemNum 
} //end Item class 

//下面是我的產品目錄類

import java.util.*; 

    public class Catalog 
    { //start class 
     private ArrayList<CatalogItem> listOfObjects = new ArrayList<CatalogItem>(100); //creates ArrayList 
    Item newItem = new Item(newItemNum, newInfo, newCost); //instantiates Item class 

    /* 
    public Catalog() 
    { //start constructor 

    } //end constructor  
    */ 

public void add(CatalogItem newItem) //method adds a new Item object to the array list 
    { //start add 
    listOfObjects.add(newItem); 

    } //end add 

    public void add(int itemNum, String info, double cost) //accepts parameters from main method to add to new object 
    { //start add 
    int newItemNum = itemNum; 
    String newInfo = info; 
    double newCost = cost; 

    newItem.setItemNum(newItemNum); 
    newItem.setInfo(newInfo); 
    newItem.setCost(newCost); 

    listOfObjects.add(newItemNum, newInfo, newCost); 

    } //end add 
}  //end class 

belo w是客戶端類。它接收來自用戶關於itemNum，info和成本的輸入

import java.util.*; //allows use of Scanner class 

public class Client 
{ //start client class 

    public static void main(String[] args) 
    { //start main 
    Catalog serv = new Catalog(); //creates instance of Catalog class 
    Scanner scan = new Scanner(System.in); //creates instance of Scanner class called scan 

    public void add(int itemNum, String info, double cost) //accepts parameters from main method to add to new object 
    { //start add 
    int newItemNum = itemNum; 
    String newInfo = info; 
    double newCost = cost; 

    newItem.setItemNum(newItemNum); 
    newItem.setInfo(newInfo); 
    newItem.setCost(newCost); 

    listOfObjects.add(newItemNum, newInfo, newCost); //adds the object to the ArrayList 

    } //end add 
} 

任何幫助將不勝感激。

Answer 1

你有一些錯誤...

在你的類目錄，這條線是不正確的：

listOfObjects.add(newItemNum, newInfo, newCost); //adds the object to the ArrayList 

你必須做到：

CatalogItem cat = new CatalogItem(newItemNum, newInfo, newCost); 
listOfObjects.add(cat); //adds the object to the ArrayList 

而在你的類客戶端，你沒有引用newItem和listOfObjects，所以你不能在那個類中使用它們。如果你想從你的客戶的主要方法添加元素listOfObjects，你可以做這樣的事情：

public class Client { 
    public static void main(String[] args) { //start main 
     Catalog serv = new Catalog(); 
     ...... 
     serv.add(1, "", 1.0d); 
    } 
}