在实例 class 中尝试输出链接列表的内容时无法从静态上下文错误中引用方法

Question

我是初学者 Java 程序员，我正在尝试检查我是否已成功将存储在 class 客户端中的链接列表中的 Person 实例复制到名为class Boat 实例中的乘客，方法是让 Boat 打印出其链表的内容。

我正在使用 class Boat 中的 givePassengers() 方法让 Boat class 打印出乘客链表内容。

然而，当我尝试这样做时，我遇到了错误 'non-static method givePassengers() cannot be referenced from a static context'，我不确定要写什么来解决这个问题。我在下面列出了我认为是问题的代码。非常感谢任何帮助。

我已经用'// !!'标记了重要代码

这是包含船

链表的class

import java.io.*;
import java.util.*;

public class Base implements Serializable
{   private LinkedList<Boat> boats = new LinkedList<Boat>();
    private Clients clients = new Clients();

public void setup() // !! Here are the instances of the boat class
    {   boats.add(new Boat(1, "Ed", 2));
        boats.add(new Boat(2, "Fred", 7));
        boats.add(new Boat(3, "Freda", 5));   }


  public void showpassengers() {

        for (Boat i: boats) `// !! The for each loop cycles through each boat to check for passengers`
           Boat.givePassengers(); // !! This line produces the error
    }

这是船class

import java.io.*;
import java.util.*;

public class Boat implements Serializable
{   private int id;
    private String pilot;
    private int stops;
    private LinkedList<Person> passengers = new LinkedList<Person>();
    private double rate = 10.00;
    public int scannableId = this.id;

 public Boat(int id, String pilot, int stops)
    {   this.id = id;
        this.pilot = pilot;
        this.stops = stops;   }



    public void givePassengers () {

System.out.println(passengers); // !! this line is supposed to print out the contents of the boat classes' linked list so I can check that it worked.

        }

这是人class

import java.io.*;
import java.text.*;

public class Person implements Serializable
{   private String name;
    private int id;
    private double cash = 100.00;
    private int start = 0;
    private int end = 0;
    private double charge = 0;

   public Person(String name, int id)
    {   this.name = name;
        this.id = id + 100; }
}

这是包含 Person

链表的 class

import java.io.*;
import java.util.*;

public class Clients implements Serializable
{   private LinkedList<Person> clients = new LinkedList<Person>();
    private int id = 1;

    public Clients() `// !! Here are the instances of Person in the class clients`
    {   clients.add(new Person("Homer", id++));
        clients.add(new Person("Marge", id++));  

    }
)

这里是根 class 如果有帮助的话

import java.io.*;

public class Root
{   public Root() {

        new Base();

    }

    public static void main(String[] args)
    {   new Root(); }


    private Base base;
}

Answer 1

您不能从 Boat 静态调用 givePassengers()，它不是静态方法。您需要从 Boat 的实例中调用它。在 foreach 循环中将 Boat.givePassengers(); 替换为 i.givePassengers();。这将导致当前选择的 Boat 实例运行 givePassengers().

Answer 2

您的问题在这里：

for (Boat i: boats) 
   Boat.givePassengers(); // !! This line produces the error

您需要说 i.givePassengers() 来引用 class Boat 的特定实例。关于 classes 和对象 here.

之间的区别，有一本很好的入门书

在实例 class 中尝试输出链接列表的内容时无法从静态上下文错误中引用方法

Cannot reference method from a static context error when attempting to output contents of linked list in instance class

java

static

linked-list