Java: static-non-static-这个问题

Question

$ javac TestFilter.java 
TestFilter.java:19: non-static variable this cannot be referenced from a static context
        for(File f : file.listFiles(this.filterFiles)){
                                    ^
1 error
$ sed -i 's@this@TestFilter@g' TestFilter.java 
$ javac TestFilter.java 
$ java TestFilter
file1
file2
file3

TestFilter.java

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

public class TestFilter {
    private static final FileFilter filterFiles;

    // STATIC!
    static{
        filterFiles = new FileFilter() {
            // Not Static below. When static, an error:
            // "accept(java.io.File) in  cannot implement 
            // accept(java.io.File) in java.io.FileFilter; 
            // overriding method is static"
            //
            // I tried to solve by the change the problem at the bottom.

            public boolean accept(File file) {
                return file.isFile();
            }
        };
    }

   // STATIC!
    public static void main(String[] args){
        HashSet<File> files = new HashSet<File>();
        File file = new File(".");

            // IT DID NOT WORK WITH "This" but with "TestFilter".
            // Why do I get the error with "This" but not with "TestFilter"?

        for(File f : file.listFiles(TestFilter.filterFiles)){
            System.out.println(f.getName());
            files.add(f);
        }
    }
}

更新:定义“当前对象”

构造函数已创建，对象已创建，但this 未引用当前对象“测试”。当我将其更改为“测试”时它有效，但它不适用于“this”。为什么？

$ javac TestFilter.java 
TestFilter.java:28: non-static variable this cannot be referenced from a static context
        for(File f : this.getFiles()){
                     ^
1 error
$ cat TestFilter.java 
import java.io.*;
import java.util.*;

public class TestFilter {

    private static final FileFilter filterFiles;
    private HashSet<File> files;

    static{
        filterFiles = new FileFilter() {
            public boolean accept(File file) {
                return file.isFile();
            }
        };
    }

    TestFilter(){
        files = new HashSet<File>();
        File file = new File(".");

        for(File f : file.listFiles(filterFiles)){
            files.add(f);
        }
    }

    public static void main(String[] args){

        // CONSTRUCTOR with no pars invoked and object "test" created here!

        TestFilter test = new TestFilter();

        // Why does it not work with "this"? 
        // "test" is surely the current object.

        for(File f : this.getFiles()){
            System.out.println(f.getName());    
        }
    }

    public HashSet<File> getFiles() { return files; }
}

Answer 1

关键字 this 引用当前的 object -- 你没有的东西，因为你的方法是静态的。这意味着它在类本身上运行，而不是在任何对象上运行，因此对 this 的任何使用都是无效的——即使您尝试访问的特定变量是静态的也。访问静态成员的正确方法是通过类:TestFilter.filterFiles，而不是 this.filterFiles。