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[英]HashMap<String, Object> : How to put Object itself as in place of String
[英]How to make an object store itself in a hashmap
所以我有 4 個類,Testest 有一個 main 方法,Phone 擴展了 Product、Product 和 ProductDB,它有一個 hashmap。 當我制作一部新手機時,我希望手機自動存儲在數據庫中。
public class Product {
protected String productID;
protected String name;
private String description;
private double price;
public Product(){
Product db = new ProductDB();
productID = this.toString();
db.add(productID, this);
}
(Getter and setter methods here...)
}
public class Phone extends Product {
private String make;
private String model;
private int storage;
public Phone(String make, String model, int storage){
this.make = make;
this.model = model;
this.storage = storage;
}
(Getter and setter methods here...)
}
import java.util.HashMap;
public class ProductDB {
private HashMap<String,Product> products = new HashMap<String, Product>();
public void add(String productID, Product product){
products.put(productID, product);
}
public void remove(String productID){
products.remove(productID);
}
public Product find(String productID){
return products.get(productID);
}
public Object showAll(){
return products.values().toArray();
}
}
public class Testest{
public static void main(String[] args){
ProductDB db = new ProductDB();
Phone phone1 = new Phone("Huwawei P30", "HP30", 50000);
Phone phone2 = new Phone("Huwawei P30 Pro", "HP30PRO", 70000);
Phone phone3 = new Phone("Samsung Galaxy SX", "SGSX", 65000);
System.out.println(db.find(phone1.productID));
System.out.println(phone1.productID);
}
}
我希望在查找該特定 ID 時返回 object,但問題是 HashMap 出於某種原因為空
編輯我將 productID 設為私有。 依然沒有
似乎您希望您的數據庫包含所有創建的電話,在這種情況下,不是每次都創建一個數據庫,這將是無用的,而且因為您的數據庫是從多個地方訪問的,所以使您的數據庫字段和方法 static 和只需從您想要的位置訪問它:
public class ProductDB {
final private static HashMap<String,Product> products = new HashMap<String, Product>();
public static void add(String productID, Product product){
products.put(productID, product);
}
public static void remove(String productID){
products.remove(productID);
}
public static Product find(String productID){
return products.get(productID);
}
public static Object showAll(){
return products.values().toArray();
}
}
然后在 Product 構造函數中只寫:
public Product{
productID = this.toString();
ProductDB.add(productID, this);
}
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