对如何实现 ArrayList 感到困惑

Question

所以我在查看 ArrayLists 时对如何向数组添加元素感到困惑，而没有为每个对象一遍又一遍地明确说明 people.add(person1)。我目前编译的这段代码没有在控制台中打印任何内容。我认为我的错误与对象构造函数和 people.add(this) 有关。我做错了什么？

import java.util.ArrayList;

public class People {

  int age;
  String name;

  static ArrayList<People> people = new ArrayList<People>();

  public People(String name, int age){
    this.name = name;
    this.age = age;
    people.add(this);
  }    

  People person1 = new People("Bob", 41);
  People person2 = new People("Arthur", 32);
  People person3 = new People("Tom",18);

  public static void main(String[] args){

    for(People p : people) {
      System.out.println(p.name);
    }
  }
}

Answer 1

数组列表是一个 static 变量。您正在创建的 People 对象是非静态变量，仅在调用构造函数时创建。您应该将对象创建移动到 main() 函数中。

public static void main(String[] args){
  People person1 = new People("Bob", 41);
  People person2 = new People("Arthur", 32);
  People person3 = new People("Tom",18);

    for(People p : people) {
      System.out.println(p.name);
    }
  }

您可以阅读有关静态变量的更多信息here

Answer 2

试试这个：

import java.util.ArrayList;

public class People {

  int age;
  String name;

  People(String name, int age){
    this.name = name;
    this.age = age;


    Main.people.add(this);
  }    

}

public class Main {

  public static ArrayList<People> people = new ArrayList<People>();

  public static void main(String[] args){

  People person1 = new People("Bob", 41);
  People person2 = new People("Arthur", 32);
  People person3 = new People("Tom",18);


    System.out.println(people.size());

    for(People p : people) {
      System.out.println(p.name);
    }
  }

}

Answer 3

您的代码稍微过于复杂了。要玩 ArrayList，您可以在 main 方法中声明 ArrayList，它本身会创建 class People 的对象并在 ArrayList 中添加人物对象。您在 People class 中创建 People class 的三个实例的方式，创建 People 对象将导致循环引用，从而导致 WhosebugError.

您应该将您的代码修改成这样，并注意为 People 对象打印有意义的信息，您需要重写 Object class 的 toString 方法，否则它只会打印可能出现的对象地址垃圾给你。

public class People {

    int age;
    String name;

    public People(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return String.format("age: %s, name: %s", age, name);
    }

    public static void main(String[] args) {
        ArrayList<People> people = new ArrayList<People>();

        People person1 = new People("Bob", 41);
        People person2 = new People("Arthur", 32);
        People person3 = new People("Tom", 18);

        people.add(person1);
        people.add(person2);
        people.add(person3);

        people.forEach(System.out::println);
    }
}

试试这个，如果遇到任何问题请告诉我。

对如何实现 ArrayList 感到困惑

Confused on how to implement an ArrayList

java

implementation

arraylist