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Customers。我希望他们在不同的班级中使用分而治之的概念，但我无法找到并移除客户。甚至有人建议我循环findCustomer来检索所有细节

  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

您对映射的声明放错了位置，它当前对findCustomer和deleteCustomer方法不可见。这两种方法中没有编译错误吗

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，将所有内容置于静态可能并不明智，尤其是当您开始使用状态时