删除方法不删除 - Java

Question

I made a program that can display and edit a record. The problem is that I cannot delete the file that I wanted to delete to replace it with the edited ones.

public class Laboratory {



public static void main(String[] args) throws FileNotFoundException,InterruptedException,IOException {
    
// paste your script here ;)
    
    String fileName = "record.txt";
    String filepath = "D:\\Programming\\Java\\Program - Script Test\\files\\" + fileName;
    
    String in = "";
    File file = new File(filepath);
    Scanner fscan = new Scanner(file);
    Scanner scan = new Scanner(System.in);
    PrintWriter pw = null;
    int linecount = 1;
    
    String content = "";
    
    // reads the file according to the given line count.
    
    for(int i = 0; i < linecount; i++) {
        
        content = fscan.nextLine();
        
    }
    
    // creates the template file.
    
    String tempPath = "D:\\Programming\\Java\\Program - Script Test\\files\\" + "temp.txt";
    
    String contentParts[] = content.split("\\|");
    
    System.out.println(content);
    System.out.println(contentParts[1]);
    System.out.println(contentParts[2]);
    
    System.out.print("change the name >> ");
    in = scan.nextLine();
    
    // edits the scanned content from the file.
    
    String finalContent = "|" + in + "|" + contentParts[2];
    
    System.out.println(finalContent);
    
    
    file = new File(filepath);
    fscan = new Scanner(file);
    
    // scans the original record and pastes it in a new template file.
    
    try {
        
        pw = new PrintWriter(new FileOutputStream(tempPath));
        
        if(linecount == 1) {
                
                content = fscan.nextLine();
                pw.println(finalContent);
                
                while(fscan.hasNextLine()) {
                    
                    content = fscan.nextLine();
                    pw.println(content);
                    
                }
                
        }
        
        else if (linecount > 1) {
            
            for (int i = 0; i < linecount - 1; i++) {
                
                content = fscan.nextLine();
                pw.println(content);
                
            }
            
            pw.println(finalContent);
            content = fscan.nextLine();
                
            while (fscan.hasNextLine()) {
                
                content = fscan.nextLine();
                pw.println(content);
                
            }
            
            
            
        }
        
        
        
    }
    
    catch(FileNotFoundException e) {
        
        System.out.println(e);
        
    }
    
    finally {
        
        pw.close();
        fscan.close();
        
    }
    
    
    
    // deletes the original record
    
    file.delete();
    
} // end of method

} // script test class end

Although, I made a test program that successfully deletes a file.

public class delete {

public static void main(String[] args) {
    
    Scanner scan = new Scanner(System.in);
    File file = new File("helloworld.txt");
    
    String in;
    
    System.out.println("Press ENTER to DELETE file.");
    in = scan.nextLine();
    
    file.delete();
    

} // main method end

} // program end

My file path is right and I don't really know what causes the problem. Is there a solution to fix this?

Answer 1

Explanation

file.delete() does not throw an error if it failed. And it failed here, as indicated by its return value being false .

Execute Files.delete(file.toPath()) instead and you will see the exact error reason, which is:

 Exception in thread "main" java.nio.file.FileSystemException: D:\Programming\Java\Program - Script Test\files\record.txt: The process cannot access the file because it is being used by another process at java.base/sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:92) at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:103) at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:108) at java.base/sun.nio.fs.WindowsFileSystemProvider.implDelete(WindowsFileSystemProvider.java:274) at java.base/sun.nio.fs.AbstractFileSystemProvider.delete(AbstractFileSystemProvider.java:105) at java.base/java.nio.file.Files.delete(Files.java:1146) at Laboratory.main(Laboratory.java:123)

So

The process cannot access the file because it is being used by another process

Because you still have a scanner to the file open, you are blocking yourself from deleting it. Close the scanner and it will work.

---

Your code opens two (not one) scanner to file , one at the beginning:

Scanner fscan = new Scanner(file);

which you use during your initial loop:

for (int i = 0; i < linecount; i++) {
    content = fscan.nextLine();
}

and then later on you create a second one:

fscan = new Scanner(file);

which you also close during your finally block:

fscan.close();

But you did never close the first scanner.

---

Solution

Add

fscan.close();

After the initial loop:

for(int i = 0; i < linecount; i++) {
    content = fscan.nextLine();
}
fscan.close();

and the file.delete() will succeed.

---

NIO

As explained, file.delete() is a poorly designed method. Prefer Files.delete(path) .

In general, if you do not have a good reason to use the old cumbersome file IO library, dont. Use NIO instead (Java 7+).