即使frame为setVisible，也无法设置Undecorated（false）

Question

In my application from a button See I display a jframe (undecorated, MAXIMIZED_BOTH, Visible and alwaysOnTop) then after some time when I am done working on it, I set it invisible from a button Close on that frame itself... But after that, when I again click the button to display the jframe, it says Exception in thread "AWT-EventQueue-0" java.awt.IllegalComponentStateException: The frame is displayable. even tough I have set the frame invisible.

Is this much information is sufficient or do you need more?

Update: My main file is FormTTS.java I also have a file named FTDirect.java , which has 3 frames: See , Blank and Main . In the Main frame I have a button See which makes the see frame visible, in the see frame after my work I make itself invisible from a button in itself and then I get returned to the main frame. Now if I again click the See button I get the error

Code: See button in Main frame in FTDirect.java

See.setUndecorated(true);
See.setVisible(true);
See.setAlwaysOnTop(rootPaneCheckingEnabled);
See.setExtendedState(MAXIMIZED_BOTH);
......

Close button in See Frame in FTDirect.java

this.setVisible(false); //That's it

Minimal example program (Pseudocodes)

File: FormTTS.java

FTdirect directform = new FTdirect();
directform.setVisible(true);
directform.setExtendedState(MAXIMIZED_BOTH);

File: FTDirect.java

//Main frame
private void MainSeeButtonActionPerformed(java.awt.event.ActionEvent evt) {                                              
    See.setUndecorated(true);
    See.setVisible(true);
    See.setAlwaysOnTop(rootPaneCheckingEnabled);
    See.setExtendedState(MAXIMIZED_BOTH);
}
//See frame - Close Button
private void jButton5ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    See.setVisible(false);
}

So concluding : I click the see button I get the See frame in there I click the close button it becomes invisible and now if I click the see button again it gives an error

Answer 1

Modify code for See method using Frame#isUndecorated() that Indicates whether this frame is undecorated. By default, all frames are initially decorated.

if (!See.isUndecorated()) {
    See.setUndecorated(true);
}
if(!See.isVisible()){
    See.setVisible(true);
}
See.setAlwaysOnTop(rootPaneCheckingEnabled);
See.setExtendedState(MAXIMIZED_BOTH);