调用构造函数时的非静态变量

Question

我正在编写代码，以从我创建的类中调用一些构造函数。

很抱歉，我的问题很简单，但我尝试到处搜索并且没有找到答案。

另一方面，我所有的课程都运行良好，没有任何错误。

当我需要从主类调用构造函数时，这给了我一个错误。

非静态变量不能从静态上下文引用。

我将发布我正在呼叫的第一堂课，并且出现错误。

public class Test1 {    

    static int nextPers = 1;

    public class Person{
    private int persID;
    private String persName;
    private String email;

    Person(int persID, String persName, String email){
        persID = nextPers;
        nextPers++;
        this.persName = persName;
        this.email = email;
    }


public static void main(String [] args){
    Person per = new Person(1 , "Raphael" , "meh@hotmail.com");
   }
}

我无法继续，程序要我放置static变量，而且我也无法弄清楚我的错误，因为当我在变量之前写入static时，它正在创建另一个错误。

Answer 1

您的类Person是Test1的内部类。

将其移动到其自己的文件或添加static关键字，如下所示：

public class Test1 {
    public static class Person {
        // your fields
    }
}

我建议阅读其他答案以获得详细说明。

Answer 2

nextPers必须是静态类成员，例如

public class Person {
    private static int nextPers = 0;

    private int persID;
    private String persName;
    private String email;

    Person(String persName, String email) {
        this.persID = nextPers++;
        this.persName = persName;
        this.email = email;
    }
}

（在您的原始代码中，您正在为persId参数分配nextPers ，我认为这不是您真正想要的，因为它用相同的名称掩盖了您的实例变量。）

Answer 3

您应该有一个用于ID的静态计数器，而不是将其提供给构造函数

public class Person {
    private int persID;
    private String persName;
    private String email;
    private static int nextPers = 0;

    Person(String persName, String email){
        this.persID = nextPers;
        nextPers++;
        this.persName = persName;
        this.email = email;
    }

    public static void main(String [] args){
        Person per = new Person("P0" , "p0@hotmail.com");
        System.out.println(per.persID + " " + per.email + " " + per.persName);
        per = new Person("P1" , "p1@hotmail.com");
        System.out.println(per.persID + " " + per.email + " " + per.persName);
        per = new Person("P2" , "p2@hotmail.com");
        System.out.println(per.persID + " " + per.email + " " + per.persName);
    }
}

Answer 4

将您的Person类放在外面，您无需将persId放入构造函数中。

package com.test;

class Person{
   private int persID;
   private String persName;
   private String email;

   Person( String persName, String email){
       this.persID = Test.nextPers;// Whenever your constructor is invoked it will assign nextPers to persId
       this.persName = persName;
       this.email = email;
       Test.nextPers++;// finally increment here
   }

   public int getPersID()
   {
      return persID;
   }

   public void setPersID( int persID )
   {
      this.persID = persID;
   }

   public String getPersName()
   {
      return persName;
   }

   public void setPersName( String persName )
   {
      this.persName = persName;
   }

   public String getEmail()
   {
      return email;
   }

   public void setEmail( String email )
   {
      this.email = email;
   }

   @Override
   public String toString()
   {
      return "Person [persID=" + persID + ", persName=" + persName + ", email=" + email + "]";
   }
}
public class Test
{
   static int nextPers = 1;

   public static void main( String[] args )
   {
      Person person1 = new Person("Raphael" , "meh@hotmail.com");
      System.out.println( person1 );
      Person person2 = new Person("Man" , "man@hotmail.com");
      System.out.println( person2 );
   }
}

输出量

Person [persID=1, persName=Raphael, email=meh@hotmail.com]
Person [persID=2, persName=Man, email=man@hotmail.com]