how can i check that a frame is open or not in java?

问题

i can open a form or another forms when button is clicked in netbeans. such as the following code

private void button1ActionPerformed(java.awt.event.ActionEvent evt) {                                               
    frame1 fr = new frame1();
    desktop.add(fr);
    fr.setVisible(true);}

but i want to control that is current form is open or close? if current form is open then when i click same button not open current form again until its closed the same form. how can i make it? there is some methods like isclosed(), isDisplayable(), but i dont khow how can i use these? please give me advice.

回答1:

You could use Boolean variables to determine whether or not the allowance of opening a frame.

example:

//declaring the boolean in a class in which both frames can access
public final class Allow {
    private Allow(){}
    public static Boolean allow_ = true;
}

In your main frame code where you open the secondary frame you can do this

if(Allow.allow_ == true) {
    Allow.allow_ = false;
    secondFrame sFrame_ = new secondFrame();
    sFrame_.setVisible(true);
} else {
    //alert the user that the frame is already open
    //I recommend a JOptionPane such as this
    JOptionPane.showMessageDialog(null, "This window is already open");
}

So now the second frame is open, and now it will only let you open it if allow_ is true.

Now when you close the second frame you do this:

Allow.allow_ = true;
secondFrame.this.setVisible(false);
secondFrame.this.dispose();

Now the second frame is closed, and will now be allowed to be opened once again.

来源：https://stackoverflow.com/questions/8777547/how-can-i-check-that-a-frame-is-open-or-not-in-java