Java: actionPerformed throws exceptions and refuses to work

Question

I am working on a program that takes a txt file which is a list of movies and selects a random movie from it. Everything is working normally but there is a GUI problem. I can't make a JLabel change text to that selected movie when I press a button.

In fact, whatever I put in the actionPerformed method refuses to work and throws a bunch of exceptions.

I do not know how to fix this since everything should be working fine(at least to me).

You can see that in the main method I called System.out.println to print out that movie from the list and it works that way. And I tried putting that same System.out.println command in actionPerformed, but it didn't work.

Here's the code: MoviePick.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class MoviePick implements ActionListener{
    private JButton button;
    private JLabel display;

    public static void main(String[] args) {
        ReadList list = new ReadList();
        MoviePick gui = new MoviePick();

        list.openFile();
        list.readFile();
        list.closeFile();

        gui.setup();

        //This works
        System.out.println(list.getRandom());
    }

    public void setup(){
        JFrame frame = new JFrame("Random Movie Picker");
        frame.setSize(250,100);
        frame.setResizable(false);
        frame.setLocationRelativeTo(null);

        button = new JButton("Get Random Movie");
        display = new JLabel("Movie");

        button.addActionListener(this);
        button.setPreferredSize(new Dimension(240,25));

        frame.setLayout(new FlowLayout(FlowLayout.CENTER));

        frame.add(display);
        frame.add(button);

        frame.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent event){
        ReadList random = new ReadList();

        //This doesn't work
        display.setText(random.getRandom());
    }
}

ReadList.java

import java.io.File;
import java.util.ArrayList;
import java.util.Scanner;

public class ReadList {
    private Scanner f;
    private ArrayList<String> theList = new ArrayList<String>();

    public void openFile(){     
        try{
            f = new Scanner(new File("list.txt"));
        }catch(Exception e){
            System.out.println("File not found!");
        }
    }

    public void readFile(){
        while(f.hasNextLine()){
            theList.add(f.nextLine());
        }
    }

    public void closeFile(){
        f.close();
    }

    public void getList(){
        for(String mov : theList){
            System.out.println(mov);
        }
    }

    public String getRandom() {
        int rand = (int) (Math.random()*theList.size());
        String chosenOne = theList.get(rand);
        return chosenOne;
    }

}

score 1 · Accepted Answer · answered Nov 03 '14 at 18:06

1

The reason it doesn't work is because you have these methods in your main method, but not in your actionPerformed one

list.openFile();
list.readFile();
list.closeFile();

Without those, these lines fail

int rand = (int) (Math.random()*theList.size());
String chosenOne = theList.get(rand);
return chosenOne;

because theList.size() is 0, so theList.get(0) throws an exception, since there is nothing in the list to get.

answered Nov 03 '14 at 18:06

resueman

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Ah yes, that fixed it. I totally forgot about those. I just moved those threee functions in actionPerformed, since I don't need it in main now, along with the object reference for ReadList. Thanks! – pandasticus Nov 03 '14 at 18:16

score 0 · Answer 2 · answered Nov 03 '14 at 18:06

Your problem is here:

public void actionPerformed(ActionEvent event){
    ReadList random = new ReadList();

    //This doesn't work
    display.setText(random.getRandom());
}

You are not opening the readlist, loading the data and closing the file like you do in main

Java: actionPerformed throws exceptions and refuses to work

2 Answers2