The display window is a core element of Processing. Once setup() is finished it will have a window and draw() ad infinitum. Herein lies a possible workaround. Is you use delay() within setup() you hold up it finishing (and thus hold up the display window). If you put delay() in a while loop and make the succesful loading of the file it's escape condition, I suppose you can tie all of this together.

" I use JFileChooser to open a txt file"
Do you know selectInput() can do that same thing "natively"? Although its usage is delicate in the latest versions...

Instead of hiding the display window, perhaps you can use it to show instructions or a kind of splash screen.

Example, reusing some code I made for another thread:

1. int buttonWidth = 200;
2. int buttonHeight = 75;
3. int buttonX = 20;
4. int buttonY = 20;
5.  
6. boolean selected;
7. File selectedFile;
8.  
9. void setup()
10. {
11.   size(500, 500);
12.   smooth();
13.  
14.   selectInput("Select a file to process", "fileSelected");
15. }
16.  
17. void draw()
18. {
19.   background(#AACCFF);
20.  
21.   if (!selected)
22.   {
23.     fill(#FF5500);
24.     textSize(20);
25.     text("Please, choose a text file", 10, 50);
26.     return; // Don't do anything until a file is selected
27.   }
28.   
29.   // Normal program
30.   boolean over = mouseX > buttonX && mouseX < buttonX + buttonWidth &&
31.       mouseY > buttonY && mouseY < buttonY + buttonHeight;
32.      
33.   drawButtonBackground(buttonX, buttonY, over);
34.   noFill();
35.   stroke(0);
36.   rect(buttonX, buttonY, buttonWidth, buttonHeight);
37. }
38.  
39. void drawButtonBackground(int x, int y, boolean light)
40. {
41.   color topColor = #AA5500;
42.   color bottomColor = #0055AA;
43.   if (light)
44.   {
45.     topColor = #FF5500;
46.     bottomColor = #0055FF;
47.   }
48.   for (int line = 0; line < buttonHeight; line++)
49.   {
50.     color sc = lerpColor(topColor, bottomColor, (float) line / buttonHeight);
51.     stroke(sc);
52.     line(x, y + line, x + buttonWidth - 1, y + line);
53.   }
54. }
55.  
56. void fileSelected(File selection)
57. {
58.   selectedFile = selection;
59.   if (selection == null)
60.   {
61.     println("Window was closed or the user hit cancel.");
62.     exit();
63.   }
64.   else
65.   {
66.     println("User selected " + selection.getAbsolutePath());
67.     selected = true;
68.   }
69. }

(I tried with frame.setVisible(false); but usage with selectInput() was inconsistent...)

Dear all
       Thank you for all your reply.I've got what I want.

1. import g4p_controls.*;
2. String fname;
3. void setup() {
4.       size(600, 200);
5.       fname = G4P.selectInput("Input Dialog");
6.       if( fname == null ){
7.             exit();
8.       }
9. }

I am back again.....The G4P.selectInput() method can't work in P3D mode.The display window still come out with the open file dialog at the same time.Still trying to work it out

As suggested above...

Code Example

1. File selectedFile;
2.  
3. void setup() {
4.   if (selectedFile==null) selectInput("Select a file", "select");
5.   while (selectedFile==null) delay(1000);
6.   size(500, 500, P3D);
7.   background(0);
8.   println("User selected " + selectedFile.toString());
9. }
10.  
11. void draw() {
12.   text(selectedFile.toString(), random(-width/2, width), random(height));
13. }
14.  
15. void select(File s) {
16.   selectedFile = s;
17. }

The G4P.selectInput() method can't work in P3D mode.The display window still come out with the open file dialog at the same time.Still trying to work it out

Sorry about that did not test it with P3D. Working version shown below.

1. import g4p_controls.*;
2. String fname = null;
3. 
   
4. void setup() {
5.   while (fname == null) {
6.     fname = G4P.selectInput("Input Dialog");
7.   }
8.   size(600, 200, P3D);
9. }
10. 
    
11. void draw() {
12.   background(255);
13.   fill(0);
14.   text(fname, 10, 40);
15. }