更新Textarea（Java）中的实例变量

Question

Im trying to create an code that will update and add an instance variable with 1 every three seconds. This is the current piece of code that I have

Timer:

 public rityta() {
        initComponents();
            //Timer
        time = new Timer(1000, null);
        time.addActionListener(this);
        time.start();
    }


public void actionPerformed(ActionEvent ae) {
    Object o = ae.getSource();
     if (o == time) {
        tid++;
        if (tid % 3 == 0) { //Every three seconds
            for (int i = 0; i < djur.size(); i++) {              //Wont start until something's been added to tha ArrayList named "djur"
                djur.get(i).setValue(djur.get(i).getValue()+1);  //Get the instance variable and adds one
                System.out.println(djur.get(i).getValue());      //Just a proof of concept that it works, the output window updated every three seconds and adds 1
                jTextArea2.update(jTextArea2.getGraphics());     // Is this needed?
            }

        }
    }
}

The Problem Now, since the output updates every three seconds with the new instance variable from my class, my Textarea that displays the instance variable should update as well, right? But it wont. So how do I make the new instance variable update in my Textarea as well?

Since my TextArea also contains the ToString of my ArrayList, the TextArea looks something like this:

Name: aaa    Value: 10
Name: bbb    Value: 10

And I just want to update the instance variable of 10 to add 1 every three seconds. :)

Answer 1

You shouldn't expect the JTextArea update automatically as you never call setText(...) or append(...) on it, and just because a variable has been changed, its String representation within the JTextArea will not automatically change when this occurs. For the JTextArea to update, either these methods must be called (setText or append) on it, or you must modify the JTextArea's Document (but do so with care).

As for this: jTextArea2.update(jTextArea2.getGraphics()); You never have a need to do this, nor should you ever want to do this.

As an aside #1, I wonder if you really want to be using a JList or JTable and not a JTextArea, but I can't say for sure without more knowledge of the details of your problem-space and your code.

Aside #2: Please consider changing your user name. You, like all of us, were born ignorant but hopefully not stupid as the former can be improved upon through diligent effort while the latter cannot.

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Regarding:

Since my TextArea also contains the ToString of my ArrayList, the TextArea looks something like this:

 Name: aaa Value: 10 Name: bbb Value: 10 

And I just want to update the instance variable of 10 to add 1 every three seconds. :)

You appear to be displaying mutable tabular data, data that changes frequently, and so in this situation I think that you're far better off using a tool that is built for just this sort of situation, a JTable. If you did this, then you would only have to change the pertinent cell's data within the JTable's model when that reference data has been updated, and since you'll wire the model to notify its view (the JTable itself) whenever it changes, your data display will automatically update.