java - ArrayList.add() 不添加到 ArrayList

Question

我试图添加一些从 PhoneBookEntry 类的构造函数创建的姓名和电话号码，将它们存储在 PhoneBook 类内的 ArrayList 中，然后能够打印出数组列表。

public class Application {
  public static void main(String[] args) {
    PhoneBookEntry name1 = new PhoneBookEntry("Cameron", "1-425-415-7157");
    PhoneBookEntry name2 = new PhoneBookEntry("Mike", "1-748-142-2341");
    PhoneBookEntry name3 = new PhoneBookEntry("Riles", "1-471-648-1782");
    PhoneBookEntry name4 = new PhoneBookEntry("Tom", "1-427-145-6471");
    PhoneBookEntry name5 = new PhoneBookEntry("Billy", "1-718-545-5715");
  }
}


import java.util.ArrayList;

public class PhoneBookEntry {

PhoneBook book = new PhoneBook();

public PhoneBookEntry(String name, String phoneNumber) {
    book.add(name, phoneNumber);
}

public void printEntries() {
    for(int i = 0; i < names.size(); i++) {
        System.out.println("Name #"+(i + 1)+": "+names.get(i));
    }
}

}


import java.util.ArrayList;

public class PhoneBook {
   ArrayList<String> names = new ArrayList<String>();
  ArrayList<String> phoneNumbers = new ArrayList<String>();

public void add(String name, String phoneNumber) {
    names.add(name);
    System.out.println(name + " added to the arraylist!");
    System.out.println(names.size());
    phoneNumbers.add(phoneNumber);
}

public void print() {
    for (int i = 0; i < names.size(); i++) {
        System.out.println("Name #" + (i + 1) + ": " + names.get(i));
    }
    for (int i = 0; i < phoneNumbers.size(); i++) {
        System.out.println("Phone Number #" + (i + 1) + ": " + phoneNumbers.get(i));
    }
}
}

当前输出:

Cameron added to the arraylist!
1
Mike added to the arraylist!
1
Riles added to the arraylist!
1
Tom added to the arraylist!
1
Billy added to the arraylist!
1

Answer 1

这是因为您为每个 PhoneBookEntry 创建了一个新的 PhoneBook，最终得到五个列表，每个列表各有一个条目。

您的代码可能看起来更像

public static void main(String[] args) {
   PhoneBook book = new PhoneBook();
   book.add("Cameron", "1-425-415-7157");
   book.add("Mike", "1-748-142-2341");
}