java - 使用 HashMap 添加、删除和查找

Question

您好，我正在使用 HashMap 添加、查找和删除客户。我希望他们分在不同的类(class)，以使用分而治之的概念，但我未能找到并删除客户。我什至建议循环 findCustomer 来检索所有详细信息。

  public static void addCustomer(){
       // Customers
    Map<String, Customer> customers = new HashMap<> ();
    customers.put ("ID1", new Customer ("Jonathan", "Mifsud", "Test Address", 21345678, "L001"));
    customers.put ("ID2", new Customer ("David", "Aguis", "2nd Address", 21456778, "L002"));
    customers.put ("ID3", new Customer ("Frank", "Mamo", "example Address", 21987653, "L003"));
  }

  public static void findCustomer(){
      //retrieve Customer Details
    System.out.println("Customer with ID1 is " + customers.get("ID1"));
  }

  public static void deleteCustomer(){
      //remove Customer Details
    System.out.println("Customer Deleted is ID3 " + customers.remove("ID3"));
  }  

Answer 1

您的 map 声明放错了位置，目前对 findCustomer 和 deleteCustomer 方法不可见。这2个方法没有编译错误吗？

您应该将其声明为 3 个方法上方的字段，如下所示:

  private static Map<String, Customer> customers = new HashMap<> ();

  public static void addCustomer(){
       // Customers
    customers.put ("ID1", new Customer ("Jonathan", "Mifsud", "Test Address", 21345678, "L001"));
    customers.put ("ID2", new Customer ("David", "Aguis", "2nd Address", 21456778, "L002"));
    customers.put ("ID3", new Customer ("Frank", "Mamo", "example Address", 21987653, "L003"));
  }

  public static void findCustomer(){
      //retrieve Customer Details
    System.out.println("Customer with ID1 is " + customers.get("ID1"));
  }

  public static void deleteCustomer(){
      //remove Customer Details
    System.out.println("Customer Deleted is ID3 " + customers.remove("ID3"));
  }  

另外，请注意，将所有内容都静态化可能并不明智，尤其是当您开始使用状态时。