for (Person person : persons) { System.out.println(person.toString()); }

这是一个 Java 的 for-each 循环语句，用于遍历一个 Person 类型的对象数组 persons，将数组中的每个元素赋值给 person 变量，然后调用 person 对象的 toString() 方法并输出到控制台。假设 Person 类型具有 toString() 方法的实现，那么输出的结果将会是 persons 数组中每个元素的字符串表示形式。

相关问题

java中如何定义如下类型变量 [{"ch_name":"王","email":"...@qq.com"},{"ch_name":"周","email":...@chinanews.com"}]

在Java中，您可以使用以下方式定义该类型变量：

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Person> persons = new ArrayList<>();
        
        Person person1 = new Person("王", "...@qq.com");
        Person person2 = new Person("周", "...@chinanews.com");
        
        persons.add(person1);
        persons.add(person2);
        
        System.out.println(persons);
    }
}

class Person {
    private String ch_name;
    private String email;
    
    public Person(String ch_name, String email) {
        this.ch_name = ch_name;
        this.email = email;
    }
    
    @Override
    public String toString() {
        return "{\"ch_name\":\"" + ch_name + "\",\"email\":\"" + email + "\"}";
    }
}

通过创建一个 `Person` 类来表示每个人，并使用 `List` 存储多个人的信息。然后，通过重写 `toString()` 方法，将对象转换为您想要的 JSON 格式。最后，将这些人的信息添加到列表中并输出结果。

请注意，这只是一种简单的示例实现，您可以根据您的需求进行修改和扩展。

Write a main method in the TestPerson.java file and in this method: 1. Declare an array of 3 Person objects. Instantiate each of the Person objects by obtaining the necessary attribute values from a user through keyboard input. 2. Call the getName(), getAddress() and getPPSNo() methods to print the information of the first person to the screen (it should be displayed exactly as the sample output below). 3. Call the setName(<…>) and setAddress(<…>) method to change the information on the second Person. 4. Use a for loop and the showPerson() method to print all the information for all People to the screen (it should be displayed exactly as the sample output below). 5. Call the toString() method on the 3rd Person object in the array.

Sure, here is an example implementation of the main method in the TestPerson.java file based on your requirements:

import java.util.Scanner;

public class TestPerson {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Person[] persons = new Person[3];

        // Instantiate each Person object by obtaining the necessary attribute values from a user
        for (int i = 0; i < persons.length; i++) {
            System.out.println("Enter details for Person " + (i + 1) + ":");
            System.out.print("Name: ");
            String name = scanner.nextLine();
            System.out.print("Address: ");
            String address = scanner.nextLine();
            System.out.print("PPS Number: ");
            String ppsNo = scanner.nextLine();
            persons[i] = new Person(name, address, ppsNo);
        }

        // Print the information of the first person to the screen
        System.out.println("Name: " + persons[0].getName());
        System.out.println("Address: " + persons[0].getAddress());
        System.out.println("PPS Number: " + persons[0].getPPSNo());

        // Change information on the second Person
        persons[1].setName("John Doe");
        persons[1].setAddress("123 Main Street");

        // Print all the information for all People to the screen
        for (Person person : persons) {
            person.showPerson();
        }

        // Call the toString() method on the 3rd Person object in the array
        System.out.println(persons[2].toString());
    }
}

Note that this implementation assumes that the `Person` class has the following methods:

public class Person {
    private String name;
    private String address;
    private String ppsNo;

    public Person(String name, String address, String ppsNo) {
        this.name = name;
        this.address = address;
        this.ppsNo = ppsNo;
    }

    public String getName() {
        return name;
    }

    public String getAddress() {
        return address;
    }

    public String getPPSNo() {
        return ppsNo;
    }

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

    public void setAddress(String address) {
        this.address = address;
    }

    public void showPerson() {
        System.out.println("Name: " + name);
        System.out.println("Address: " + address);
        System.out.println("PPS Number: " + ppsNo);
    }

    @Override
    public String toString() {
        return "Person{name='" + name + "', address='" + address + "', ppsNo='" + ppsNo + "'}";
    }
}

Sample output:

Enter details for Person 1:
Name: Alice Smith
Address: 456 Elm Street
PPS Number: 1234567A
Enter details for Person 2:
Name: Bob Johnson
Address: 789 Oak Road
PPS Number: 1234567B
Enter details for Person 3:
Name: Claire Davis
Address: 1010 Maple Avenue
PPS Number: 1234567C
Name: Alice Smith
Address: 456 Elm Street
PPS Number: 1234567A
Name: John Doe
Address: 123 Main Street
PPS Number: 1234567B
Name: Claire Davis
Address: 1010 Maple Avenue
PPS Number: 1234567C
Person{name='Claire Davis', address='1010 Maple Avenue', ppsNo='1234567C'}