Question

我正在尝试使用JOptionPane显示我的人物对象（姓名，年龄）。（名称和年龄是命令行参数中的字符串和整数）。但是，我收到以下错误：

BasicClass.java:9: error: non-static variable this cannot be referenced from a static context
      Person person1 = new Person(args[0], age1);
                       ^

BasicClass.java:10: error: non-static variable this cannot be referenced from a static context
      Person person2 = new Person(args[2], age2);
                       ^

我是否正确地将第一个Person对象初始化为命令行输入？

修改的对不起，我忘了我的代码示例：

import javax.swing.JOptionPane;

public class BasicClass{
   public static void main(String[] args){
      Integer age1 = Integer.parseInt(args[1]);
      Integer age2 = Integer.parseInt(args[3]);

   // Create two Person Objects
      Person person1 = new Person(args[0], age1);
      Person person2 = new Person(args[2], age2);

   // toString() method to display first & second Person Object
      String firstOutput = person1.toString();
      String secondOutput = person2.toString();
      JOptionPane.showMessageDialog(null, firstOutput);
      JOptionPane.showMessageDialog(null, secondOutput);
   }

   // Object
   class Person{
   // Data fields that will store each of the objects data
      private String name;
      private Integer age;

   // Constructor
      public Person(String n1, int a1){
         name = n1;
         age = a1;
      }

      public String toString(){
         String output = name + " is" + age + " years old.";
         return output;
      }
   }
}

Answer 1

Person是非静态内部类，这意味着它是外部类（BasicClass）实例的成员，如果没有此实例，则无法使用它（就像方法或字段）。

由于您在静态方法和静态方法中使用此类，因此没有默认的this引用

制作Person课程static
或创建外部类的实例，您将通过该实例创建Person类的实例，如
```
BasicClass basic = new BasicClass();
Person p = basic.new Person();
```
或将Person课程的代码放在BasicClass课程之外。

Answer 2

这是因为您在静态上下文中调用非静态类。一种方法是在主类中创建Person对象，然后创建主类对象。否则，您应该将Person类声明为静态类，例如

import javax.swing.JOptionPane;

public class Main{
   public static void main(String[] args){
      Integer age1 = Integer.parseInt(args[1]);
      Integer age2 = Integer.parseInt(args[3]);

   // Create two Person Objects
      Person person1 = new Person(args[0], age1);
      Person person2 = new Person(args[2], age2);

   // toString() method to display first & second Person Object
      String firstOutput = person1.toString();
      String secondOutput = person2.toString();
      JOptionPane.showMessageDialog(null, firstOutput);
      JOptionPane.showMessageDialog(null, secondOutput);
   }

   // Object
   static class Person{
   // Data fields that will store each of the objects data
      private String name;
      private Integer age;

   // Constructor
      public Person(String n1, int a1){
         name = n1;
         age = a1;
      }

      public String toString(){
         String output = name + " is" + age + " years old.";
         return output;
      }
   }
}

请参阅another example。

从类错误Java创建新对象

2 个答案: