我们如何为java中的对象数组中的嵌套类创建实例？

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，我确实理解employee_address 是一个类，如果没有像代码中那样创建实例，就不能直接访问它，这是没有意义的。 但是如何创建与每个员工关联的 employee_address 类的实例。

就像上面的代码中的“employee_address”与每个员工相关联，但是如何初始化“employee_address”类以及如何设置地址类中的街道名称、城市和其他成员。 任何想法，将不胜感激。

Answer 1

下面的代码使用Java 命名约定（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();
        }
    }
}

内部类是一个普通类。 它不是其封闭类的成员。 如果您希望Employee类具有 [employee] 地址以及 [employee] 名称，则需要向Employee类添加另一个成员变量，其类型为EmployeeAdress 。

Employee[] employeesList = new Employee[noOfEmployees];

上面的行创建了一个数组，但数组中的每个元素都为空。 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，我上面的代码中有以下行：

employeesList[i] = new Employee();

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

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

由于您的所有代码都在Employee类中，因此在main方法中您可以直接访问Employee类和EmployeeAddress类的成员。 尽管如此，您需要了解 java 中的不同访问修饰符。

Answer 2

不能直接创建内部类的实例，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。

假设你有一个类，它有两个属性：

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

要访问您需要通过Employee类的实例使用的emAddress ，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。

Answer 3

一些提示：

1. 遵守命名约定：Java 中的类名以大写字母开头
2. 在使用它们之前使用（类）定义（如果不方便，将它们收集在顶部）
3. 如果您确定要使用内部类，请将它们设置为静态，除非您希望它们与泛型纠缠在一起。
4. 通常每个文件中的普通类都更加灵活且易于使用
5. 如果您使用只携带公共数据的对象，请尝试使用 final 关键字并尽快初始化它们
6. 首先使用适当的对象，完成后将它们分配给数组。 avan 更好的是使用ArrayList等
7. 如果 Employee 包含EmployeeAddress ，它应该在方便时初始化它。 所以一个对象总是对它自己的东西负责
8. 使用 try/resrouce/catch
9. scanner.nextInt()可能会出现换行符/换行符的问题。 对于用户输入更好的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
            }

        }
    }



}