NullPointerException while calling getter JFileChooser

Question

I'm getting a NullPointerException every time I call a getter. Here's the code:

import java.io.File;
import javax.swing.JFileChooser;
import javax.swing.filechooser.FileNameExtensionFilter;

public class FileChooser extends JFileChooser {
private int result;
private File filename;
private File subFile;
private FileNameExtensionFilter filter;

    public FileChooser() {
        filename = new File(System.getProperty("user.home"));
        filter = new FileNameExtensionFilter("Subtitle Files (*.srt)", "srt");
    }

    public void createAndShowGUI() {
        this.setDialogTitle("Select a file");
        this.setCurrentDirectory(filename);       
        this.setFileFilter(filter);
        result = this.showOpenDialog(this);
        if(result == JFileChooser.APPROVE_OPTION) 
            subFile = this.getSelectedFile();   
        this.setVisible(true);        
    }

    public File getFile() {
        return subFile;
    }

}

I get null pointer everywhere I use the variable that calls the getFile() function. foo in this case. Here's the snippet:

FileChooser fileChooser = new FileChooser();
File foo = fileChooser.getFile();
System.out.println(foo.getName()); //Null-Pointer
System.out.println(foo.getPath()); //Null-Pointer

UPDATE: I happen to have two instances of FileChooser but, I would like to call createAndShowGUI() only once. How do I initialise the selected file in the constructor ?

You should probably initialize subFile in the constructor also. — aleksandar, Jul 02 '15 at 19:28
Just cut the code in "createAndShowGUI" and paste it in the constructor. Now you don't need to call the function and it should work ok. — aleksandar, Jul 02 '15 at 19:38
Pass it as an argument to the constructor and initialize it. (for the update) — aleksandar, Jul 02 '15 at 19:46

score 2 · Answer 1 · answered Jul 02 '15 at 19:26

2

Well you are never calling createAndShowGUI(). Just call that before you call getFile()

answered Jul 02 '15 at 19:26

TameHog

950
11
23

Shrinivas Shukla · Answer 2 · 2015-07-02T19:50:20.440

1

According to your code, the field subFile is initialized in the method createAndShowGUI() inside the if condition.

But, as you are not calling the method createAndShowGUI() the field subFile remains null when you call getFile().

Try this code,

FileChooser fileChooser = new FileChooser();
fileChooser.createAndShowGUI();             // MISSING IN ORIGINAL CODE
File foo = fileChooser.getFile();
System.out.println(foo.getName()); //Null-Pointer
System.out.println(foo.getPath()); //Null-Pointer

UPDATE

As the question is updated with

I happen to have two instances of FileChooser but, I would like to call createAndShowGUI() only once

If you call createAndShowGUI() only once then the user will be able to select the file only once.

Then what is the use of creating two instances of FileChooser?

You need to call createAndShowGUI() every time you create a new instance of FileChooser.

edited Jul 02 '15 at 19:50

answered Jul 02 '15 at 19:27

Shrinivas Shukla

4,325
2
21
33

I call it in the main function before calling `getFile()` – Jimmy Jul 02 '15 at 19:30
You need to call `createAndShowGUI()` after you make an instance of `FileChooser`. – Shrinivas Shukla Jul 02 '15 at 19:34
I added a code snippet to my answer. That should solve the purpose. – Shrinivas Shukla Jul 02 '15 at 19:36

score 1 · Accepted Answer · answered Jul 02 '15 at 19:40

import java.io.File;
import javax.swing.JFileChooser;
import javax.swing.filechooser.FileNameExtensionFilter;

public class FileChooser extends JFileChooser {
    private int result;
    private File filename;
    private File subFile;
    private FileNameExtensionFilter filter;

    public FileChooser() {
        filename = new File(System.getProperty("user.home"));
        filter = new FileNameExtensionFilter("Subtitle Files (*.srt)", "srt");
        this.setDialogTitle("Select a file");
        this.setCurrentDirectory(filename);       
        this.setFileFilter(filter);
        result = this.showOpenDialog(this);
        if(result == JFileChooser.APPROVE_OPTION) 
            subFile = this.getSelectedFile();   
        this.setVisible(true);
    }

    public File getFile() {
        return subFile;
    }

}

score 0 · Answer 4 · answered Jul 02 '15 at 19:27

0

I think this is problem:

if(result == JFileChooser.APPROVE_OPTION) 
        subFile = this.getSelectedFile();

result == JFileChooser.APPROVE_OPTION return false and subFile never initialized

answered Jul 02 '15 at 19:27

Bohdan Zv

442
2
5
22

NullPointerException while calling getter JFileChooser

4 Answers4