Question

很抱歉，之前可能已经提出过这个问题了，但是在上下文中我找不到任何答案，这些答案特别适用于我的问题，以便我应用解决方案。

无论如何，我正在研究一个使用文件的程序。当该文件更新时，我希望它将File变量替换为当前变量。我设置了一个可以使用该文件的主类，然后我设置了另一个具有不同线程的类来监听文件更新。当文件更新时，我希望更新主类中的变量。

这意味着更新侦听器类必须具有主类的实例，但是当我尝试在启动更新侦听器类期间发送它时，警告表示无法从静态上下文引用主类。 / p>

以下是代码：

主要类

package me.xeyler;

import com.sun.media.jfxmedia.logging.Logger;

import javax.swing.*;
import java.awt.Color;
import java.io.File;
import java.io.IOException;
import java.nio.file.*;

import static java.nio.file.StandardWatchEventKinds.*;

/**
 * Created by Brigham on 10/19/2016.
 */
public class ViewerMain {

    static FileHandler fileHandler;
    static File skinFile;

    public static void main(String[] args) {

        boolean bool = false;

        fileHandler = new FileHandler(this);
        fileHandler.start();
        while(true) {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(bool);
        }

    }

    public void setSkinFile(File skinFile) {
        this.skinFile = skinFile;
    }
}

文件侦听器类

package me.xeyler;

import com.sun.media.jfxmedia.logging.Logger;

import javax.swing.*;
import java.awt.*;
import java.io.File;
import java.io.IOException;
import java.nio.file.*;

import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;

/**
 * Created by Brigham on 10/19/2016.
 */
public class FileHandler implements Runnable {

    private Thread fileThread;
    private String threadName;
    WatchService watcher = null;
    private ViewerMain main;

    public FileHandler(ViewerMain main) {

        this.main = main;
        this.threadName = "FileThread";

    }

    public void watchFile(Path path) {

    }

    public void watchFile(File file) {

        watchFile(Paths.get(file.getPath()));

    }

    public void close() {
        try {
            watcher.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void start () {
        if (fileThread == null) {
            System.out.println("Starting new thread...");
            fileThread = new Thread (this, threadName);
            fileThread.start();
            System.out.println("Started thread: " + threadName);
        }
    }

    @Override
    public void run() {

        System.out.println("Running thread...");

        Path dir = Paths.get(System.getProperty("user.home"),"documents");
        try {
            watcher = FileSystems.getDefault().newWatchService();
            WatchKey key = dir.register(watcher,
                    ENTRY_MODIFY);
        } catch (IOException x) {
            x.printStackTrace();
        }

        for (;;) {

            // wait for key to be signaled
            WatchKey key;
            try {
                key = watcher.take();
            } catch (InterruptedException x) {
                return;
            }

            for (WatchEvent<?> event: key.pollEvents()) {
                WatchEvent.Kind<?> kind = event.kind();

                // The filename is the
                // context of the event.
                WatchEvent<Path> ev = (WatchEvent<Path>)event;
                Path filename = ev.context();

                if (filename.endsWith("text.txt")) {
                    System.out.println("File has changed");
                    //TODO: Update File variable in ViewerMain
                    main.setSkinFile(filename.toFile());
                }

            }

            // Reset the key -- this step is critical if you want to
            // receive further watch events.  If the key is no longer valid,
            // the directory is inaccessible so exit the loop.
            boolean valid = key.reset();
            if (!valid) {
                // TODO: Handle inaccessible directory
                break;
            }
        }

    }
}

我怀疑答案非常明显，但感谢耐心！

Answer 1

如果我理解正确，您需要ViewerMain类的实例。

this无法在静态上下文中应用。

public static void main(String[] args) {

    ViewerMain viewer = new ViewerMain(); // an instance
    fileHandler = new FileHandler(viewer);

skinFile

相同

public File skinFile; // Remove static

public void setSkinFile(File skinFile) {
    this.skinFile = skinFile;
}

Answer 2

你不能这样做：

public void setSkinFile(File skinFile) {
    this.skinFile = skinFile;
}

因为skinFile是静态的，所以如果将该属性设置为public static File skinFile;然后直接从FileHandler加入属性会更好：

ViewerMain.skinFile = filename.toFile()

鉴于它是一个静态属性，你不需要类的实例来访问它，你可以直接使用该类。

静态类的Java引用

2 个答案: