我们如何为 java 中的对象数组中的嵌套 class 创建一个实例？

Question

import java.util.Arrays;
import java.util.Scanner;

public class employee{
    public String name;
    public class employee_address{
        String street_name;
        String city;
        String zipcode;
        String state;
        String country;
    }

    public static void main(String []args){
        Scanner user_input = new Scanner(System.in);

        int no_of_employees = user_input.nextInt();
        employee[] employees_list = new employee[no_of_employees];
        for(int i = 0;i < no_of_employees;i++){
            employees_list[i].name = user_input.nextLine();
            employees_list[I].employee_address = // this is it ? 
        }
    }
}

在上面的代码中，我明白 employee_address 是一个 class 并且无法访问直接在没有像代码中那样创建实例的情况下，这是没有意义的。但是我如何创建与每个员工关联的 employee_address class 的实例。

就像上面的代码 'employee_address' 与每个员工相关联，但是如何初始化 class 'employee_address' 以及如何设置 street_name、城市和地址 class 中的其余成员。任何想法将不胜感激。

Answer 1

一些提示：

遵守命名约定：class Java 中的名称以大写字母开头
在使用它们之前使用 (class) 定义（如果不方便，请将它们收集在顶部）
如果您确定要使用内部 classes，请将它们设置为静态，除非您希望它们与泛型纠缠在一起。
通常每个文件中的普通 classes 更加灵活且更易于使用
如果您使用的对象只携带 public 数据，请尝试使用 final 关键字并尽快初始化它们
先使用合适的对象，完成后赋值给数组。 avan 更好的方法是使用 ArrayList 之类的
如果Employee包含EmployeeAddress，方便的话应该初始化一下。所以一个对象总是对它自己的东西负责
使用try/resrouce/catch
scanner.nextInt() 可能会因 newline/line 中断而出现问题。对于用户输入更好 readLine() 和解析输入

代码：

import java.io.PrintStream;
import java.util.ArrayList;
import java.util.Scanner;

public class Employee {


    static public class EmployeeAddress {
        public final String street_name;
        public final String city;
        public final String zipcode;
        public final String state;
        public final String country;
        public EmployeeAddress(final Scanner pScanner, final PrintStream pOutPS) {
            street_name = readLine(pScanner, pOutPS, "Please enter Street Name:");
            city = readLine(pScanner, pOutPS, "Please enter City Name:");
            zipcode = readLine(pScanner, pOutPS, "Please enter Zip Code:");
            state = readLine(pScanner, pOutPS, "Please enter State:");
            country = readLine(pScanner, pOutPS, "Please enter Country:");
        }
    }

    static public String readLine(final Scanner pScanner, final PrintStream pOutPS, final String pPrompt) {
        pOutPS.print(pPrompt);
        final String value = pScanner.nextLine();
        pOutPS.println();
        return value;
    }
    static public int readInt(final Scanner pScanner, final PrintStream pOutPS, final String pPrompt) {
        return Integer.parseInt(readLine(pScanner, pOutPS, pPrompt));
    }



    public final String             name;
    public final EmployeeAddress    address;

    public Employee(final Scanner pScanner, final PrintStream pOutPS) {
        name = readLine(pScanner, pOutPS, "Please enter Employee Name: ");
        System.out.println("Name: " + name);
        address = new EmployeeAddress(pScanner, pOutPS);
    }



    public static void main(final String[] args) {
        try (final Scanner user_input = new Scanner(System.in);
                final PrintStream output = System.out;) {

            final int no_of_employees = readInt(user_input, output, "Please enter number of users: ");

            final Employee[] employees_list = new Employee[no_of_employees]; // either this line
            final ArrayList<Employee> employees = new ArrayList<>(); // or this line

            for (int i = 0; i < no_of_employees; i++) {
                output.println("Creating user #" + (i + 1) + "...");
                final Employee newEmployeeWithAddress = new Employee(user_input, output);

                employees_list[i] = newEmployeeWithAddress; // either this line
                employees.add(newEmployeeWithAddress); // or this line
            }

        }
    }



}

Answer 2

下面的代码使用 Java naming conventions（您的代码没有）。

代码后的注释。

import java.util.Scanner;

public class Employee {
    private String name;
    private EmployeeAddress address;

    public class EmployeeAddress {
        String streetName;
        String city;
        String zipcode;
        String state;
        String country;
    }

    public static void main(String[] args) {
        Scanner userInput = new Scanner(System.in);
        int noOfEmployees = userInput.nextInt();
        Employee[] employeesList = new Employee[noOfEmployees];
        for (int i = 0; i < noOfEmployees; i++) {
            employeesList[i] = new Employee();
            employeesList[i].name = userInput.nextLine();
            EmployeeAddress employeeAddress = employeesList[i].new EmployeeAddress();
            employeesList[i].address = employeeAddress;
            employeesList[i].address.streetName = userInput.nextLine();
        }
    }
}

内部class是正常的class。它不是其封闭 class 的成员。如果想让classEmployee有[员工]地址，还有[员工]姓名，需要在classEmployee中再增加一个成员变量，其类型是 EmployeeAdress.

Employee[] employeesList = new Employee[noOfEmployees];

上面一行创建了一个数组，但数组中的每个元素都是空的。因此，您需要首先创建一个 Employee 对象并将其分配给数组的一个元素。因此，上面我的代码中的以下行：

employeesList[i] = new Employee();

由于 EmployeeAddress 不是静态 class，为了创建一个新实例，您首先需要一个封闭 class，即 Employee。因此，上面代码中的以下行。

EmployeeAddress employeeAddress = employeesList[i].new EmployeeAddress();

由于所有代码都在 class Employee 中，在方法 main 中，您可以直接访问 class Employee 和 EmployeeAddress。尽管如此，您还是需要注意 java.

中的不同 access modifiers

Answer 3

你不能直接创建 inner class 的实例，原因是因为它是另一个实例的属性，我们总是需要通过父变量的实例来使用它。

假设您有一个 class，它有两个属性：

public class Employee {
    public String name;
    public EmployeeAddress emAddress;
}

访问emAddress你需要通过Employeeclass的实例来使用，例如-

Employee object = new Employee();
EmployeeAddress empAdd = object.new EmployeeAddress();

完整代码：

public class Employee {
    public String name;
    public EmployeeAddress emAddress;

    public class EmployeeAddress {
        String street_name;
        String city;
        String zipcode;
        String state;
        String country;
        public String getStreet_name() {
            return street_name;
        }
        public void setStreet_name(String street_name) {
            this.street_name = street_name;
        }
        public String getCity() {
            return city;
        }
        public void setCity(String city) {
            this.city = city;
        }
        public String getZipcode() {
            return zipcode;
        }
        public void setZipcode(String zipcode) {
            this.zipcode = zipcode;
        }
        public String getState() {
            return state;
        }
        public void setState(String state) {
            this.state = state;
        }
        public String getCountry() {
            return country;
        }
        public void setCountry(String country) {
            this.country = country;
        }
        @Override
        public String toString() {
            return "EmployeeAddress [street_name=" + street_name + ", city=" + city + ", zipcode=" + zipcode
                    + ", state=" + state + ", country=" + country + "]";
        }
        
        
    }

    public static void main(String[] args) {
        Scanner user_input = new Scanner(System.in);

        int no_of_employees = user_input.nextInt();  // let's say no_of_employees =  1
        Employee[] employees = new Employee[no_of_employees];
        for (int i = 0; i < no_of_employees; i++) {
            Employee object = new Employee();
            object.setName("Virat Kohli");
            
            EmployeeAddress empAdd = object.new EmployeeAddress();
            empAdd.setCity("New Delhi");
            empAdd.setCountry("India");
            empAdd.setState("Delhi");
            empAdd.setStreet_name("Chandni Chalk");
            empAdd.setZipcode("741124");
            
            object.setEmAddress(emAddress);
            employees[i] = object;          
        }
        
        System.out.println(employees[0]);
        
        user_input.close();
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public EmployeeAddress getEmAddress() {
        return emAddress;
    }

    @Override
    public String toString() {
        return "Employee [name=" + name + ", emAddress=" + emAddress + "]";
    }

    public void setEmAddress(EmployeeAddress emAddress) {
        this.emAddress = emAddress;
    }
}

我已将您的代码修改为 sonar 标准。

我们如何为 java 中的对象数组中的嵌套 class 创建一个实例？

How can we create an instance for a nested class in array of objects in java?

java

inner-classes