How can code use an object inside a button?

Question

I have an issue. I want to use my object which is outside a button, and I get an error message:

Local variable es defined in an enclosing scope must be final or effectively final

File inputfile = new File("./input.txt");
testobject to = null;
try {
    Scanner inputscan = new Scanner(inputfile);
    String text1 = inputscan.nextLine();
    String text2 = inputscan.nextLine();
    to = new testobject(text1,text2);

    inputscan.close();
} catch (Exception e)  {
    System.err.println(e);
}

JButton btnSave = new JButton("Save");
btnSave.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        to.setSomething("test");
    }
});

Obviously, I have a class with a constructor etc... but I have a problem that I cant reach my object inside the button.

You can implement the ActionListener interface on your `testobject`, or you can create a class that implement the ActionListener and that receive in input the `testobject` instance. Of course you still have the problem that your `tesobject` instance can be null. — Mario Santini, Nov 21 '21 at 09:08

magicmn · Answer 1 · 2021-11-21T09:39:17.730

Variables that you want to use inside anonymous classes, like your ActionListener need to be final. You are initializing the variable with null and change it to the object created from the text input later.

You could instead create the object using a no args constructor and use setters to set the value in your testobject.

// Class names should start with a uppercase
testobject to = new testobject();
// Use try-with-resources to close them automatically.
try(Scanner inputscan = new Scanner(inputfile)){
    to.setText1(inputscan.nextLine());
    to.setText2(inputs can.neytLine());
 } catch (Exception e) {
    System.err.println(e)
 }
JButton btnSave = new JButton("Save");
btnSave.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        to.setSomething("test");
    }
});

Or initialize the variable inside your actionPerfromed method. The downside is that you can't access the testobject outside of the method.

btnSave.addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {
         try(Scanner inputscan = new Scanner(inputfile)){
             testobject to = new testobject(inputscan.nextLine(), inputscan.nextLine());
             to.setSomething("test");
         } catch (Exception e) {
            System.err.println(e)
         }
     }
});

copy14 · Accepted Answer · 2021-12-01T20:26:51.443

I tried the first method, maybe I did something worng but it didn't work. The second method is working, but this create a new object in the button, so if I want to use outside a button, I need to set everything again. And in my program it is very complicated etc...

So the solution I created an Arraylist and I can use this inside and outside the button too.

ArrayList<testobject> list = new ArrayList<testobject>();

And after this I set the first (0) element to my data

list.add(new testobject(text1,text2));

And after this I can easily use easily the methods of the class

list.get(0).setSomething("test");

How can code use an object inside a button?

2 Answers2