用 Java swing 等待一个事件

Question

I've got a Java class called "Text" which uses swing to create 2 textboxes. There's a listener in it that copies text from the first box to the end of the second box. So far I have it set up to where other classes can call a function to output text to the second box.

What I want to do is have a function that causes the program to wait until the user enters a string of text and presses enter (which would trigger the event listener I already have), and then returns that string of text to a user.

I tried doing something like:

String lastInput;
boolean waiting;

    public void actionPerformed(ActionEvent evt) {
        String text = textField.getText();
        println(text);
        lastInput = text;
        waiting = false;
        parse(text);
        textField.selectAll();
    }

    public String get() {
        waiting = true;
        while(waiting){}
        return lastInput;
    }

But this just causes the program to freeze and not register any input (including any typing in the textbox). I'm pretty sure that I'd need to make use of java's thread system, but I've never used it before and I can't find anything online about how I could use it to solve this problem in particular.

Thanks!

Answer 1

I'm pretty sure that I'd need to make use of java's thread system,

That is not how you design a GUI. Generally a GUI sits there doing nothing. Think of your browser, it only does something when the user generates an event, for example, by using the keyboard or the mouse.

I want to do is have a function that causes the program to wait until the user enters a string of text and presses enter

If you want to prompt the user to enter text then you should probably use a JOptionPane . Read the Swing tutorial on How to Make Dialogs for some examples.

If you truly have a situation where you need to do processing when text is entered in a text field of a form then you would add an ActionListener to the text field.

See: How to Use Text Fields .

The TextDemo example will copy text from the text field to the text area when Enter is pressed on the text field.

Answer 2

First, the main issue here is the while loop, which is an infinite loop. If you use a single thread, then once the loop is executed, there will be no free context that can invoke the "actionPerformed" method.

The main issue is having a different contexts: one will be executing the "get" method, and one will be executing the "actionPerformed" once the trigger invoked.

Two more things:

1. Your "get" function name is bad, and may be confusing. Get is used for getters (accessing class'es members).
2. Use a thread-safe waiting boolean (AtomicBoolean or something).