Question

我正在编写一个用java连接到控制台像素示例草图的程序。我仍然是新的，我得到了这个错误：

非静态变量fast不能从静态上下文引用

我不知道错误意味着什么，但我的代码是：

package javaapplication5;

import java.net.*;
import java.io.*;
import java.util.Scanner;
/**
 *
 * @author preferreduser
 */
public class JavaApplication5 {
    int fast = 0;
    public static void main(String[] args) throws IOException {
        Scanner x = new Scanner(System.in);
        System.out.print("Yun ip: ");
        String IP = x.nextLine();
        System.out.println("Loding...");
        try {
            // Create a URL for the desired page
            URL url = new URL("http://"+ IP +"/arduino/digital/13/1");       

            // Read all the text returned by the server
            BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
            in.close();
        } catch (MalformedURLException e) {
        } catch (IOException e) {
        }
        try {
            // Create a URL for the desired page
            URL url = new URL("http://"+ IP +"/arduino/digital/13/0");       

            // Read all the text returned by the server
            BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
            in.close();
        } catch (MalformedURLException e) {
        } catch (IOException e) {
        }
        System.out.println("Connected to YUN on "+ IP);
        OUTER:
            while (true) {
                Scanner y = new Scanner(System.in);
                System.out.print("> ");
                String str = y.nextLine();
                switch (str) {
                case "on":
                    try {
                        // Create a URL for the desired page
                        URL url = new URL("http://"+ IP +"/arduino/digital/13/1");

                        // Read all the text returned by the server
                        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                        in.close();
                    } catch (MalformedURLException e) {
                    } catch (IOException e) {
                    }               break;
                case "off":
                    try {
                        // Create a URL for the desired page
                        URL url = new URL("http://"+ IP +"/arduino/digital/13/0");

                        // Read all the text returned by the server
                        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                        in.close();
                    } catch (MalformedURLException e) {
                    } catch (IOException e) {
                    }               break;
                case "help":
                    System.out.println("");
                    System.out.println("on   exit");
                    System.out.println("off  help");
                    System.out.println("");
                    break;
                case "exit":
                    try {
                        // Create a URL for the desired page
                        URL url = new URL("http://"+ IP +"/arduino/digital/13/0");

                        // Read all the text returned by the server
                        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
                        in.close();
                    } catch (MalformedURLException e) {
                    } catch (IOException e) {
                    }               break OUTER;
                }
                if ( fast == 1 ){
                    URL oracle = new URL("http://"+ IP +"/arduino/digital/13");
                    try (BufferedReader in = new BufferedReader(
                            new InputStreamReader(oracle.openStream()))) {
                        String inputLine;
                        while ((inputLine = in.readLine()) != null)
                            System.out.println(inputLine);
                    }
                } else {System.out.println("Success");}
            }
    }
}

我想连接到arduino yun并输入像on或off这样的命令，并且该部分有效。我想快速添加一个可选选项，以便在每次输入命令时更快地连接到http：// * / aruino / digital / 13。这是我的开始。我要为它添加一个命令，但是直到我弄清楚它才能得到它

Answer 1

您只能通过class来直接访问static的成员变量。 Om使变量static更多的方法来访问它是class_name.variable_name。

否则您必须object class，然后您可以通过该对象访问该变量。

示例：

要么改变

int fast=0;至static int fast = 0;

或者你这样做

JavaApplication5 j5 = new JavaApplication5();现在按j5.fast访问变量并进行进一步计算。

Answer 2

将int fast = 0;更改为static int fast = 0;

您在main方法中使用变量fast，这是一种静态方法。在任何静态方法中使用的所有变量都应该是静态的。原因是静态方法对于一个类来说很常见，它不依赖于类的实例。因此，它不能使用任何实例变量（除非您指定要使用的特定实例），因为该方法不知道要使用哪个实例变量。

无法从静态上下文java

2 个答案: