Java AWT setLayout（null）似乎不起作用

Question

I'm trying to re-purpose an existing Java AWT (stand alone) application to run on dedicated, single-purpose hardware (think a kiosk in a museum that also controls hardware behind the scenes) and my presumption that if I simply set the layout manager on my main panel to null I'd be able to lay out items using something like Rectangle(starting x, starting y, x-width, y-height) or perhaps another similar method to position things, has proven false! So, I'm more lost than I thought I would be!

Here are a few excerpts:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
[...]
public class myGUI extends JFrame
{
  JPanel MainPanel = new JPanel();
  JMenuBar Menu = new JMenuBar();
  int MaxWidth = 1920;
  int MaxHeight = 1080;
  Dimension FullScreen = new Dimension(MaxHeight, MaxWidth);
  Rectangle recHZbar = new Rectangle(0, 32, MaxWidth, 4);
[...]
    MainPanel.setLayout(null);
    MainPanel.setPreferredSize(FullScreen);
    MainPanel.setEnabled(true);
    MainPanel.setBackground(LightBlue);

There are all manner of components totaling around a hundred or so and it makes no sense to present them here. Suffice to say that I'm trying to eliminate what were stand-alone frames and instead present all the data around the edges of a very large screen and then manage the center space of the screen separately with key data, hopefully able to use visibility to switch what the user sees (instead of panes / panels), since in many cases there's a lot of commonality.

I thought that by setting the layout manager to null I would then be able to position components on MainPanel using something like this horizontal bar with a message embedded in it:

JLabel HorizontalBar = new JLabel();
HorizontalBar.setBackground(DarkBlue);
HorizontalBar.setFont(new java.awt.Font("Dialog", 0, 10));
HorizontalBar.setForeground(LightBlue);
HorizontalBar.setPreferredSize(dimMxW10pt);
HorizontalBar.setOpaque(true);
HorizontalBar.setHorizontalTextPosition(SwingConstants.CENTER);
HorizontalBar.setText(HZBarTxt);
HorizontalBar.setBounds(recHZbar);
MainPanel.add(HorizontalBar, null);

... And this, of course, works, BUT, when I tried to position this horizontal bar (via setBounds(rectangle) ), it's apparent that the coordinates are based off of the bottom of the JMenuBar I added earlier, and NOT from the upper left corner of the screen! This has me rather concerned! (I presume the next bar will be based on the space below the first one, etc?!) Am I correct in thinking I've got a layout manager I didn't (explicitly) ask for? (If so, how do I avoid it?)

I'm hoping I'm overlooking something simple to be able to do positioning myself without having to go through too much work. If I can't just pick where I want things to be on the screen, I'm going to be in trouble on this project! I'm hoping to avoid lots of little panels and such. I need to create irregular columns and so forth. I know I can do the math to lay things out how I want, and I'm loathe to trust a layout manager to get it right, especially since the testing on the actual production hardware is very hard, and if the layout manager is different, it'll mean trouble. I may well be I'm overlooking the right layout manager - the "do it yourself layout manager", perhaps? - but I don't see how "GridLayout" is going to work for me, at least, not easily. So I'm hoping to learn how to do my own layout as simply and directly as possible (which is what I thought I was already doing).

TIA.

Answer 1

It turns out that my original assumption that the call to setLayout(null) hadn't worked was itself mistaken, and that's a good thing!

Given MY requirements, I made the exactly correct choice of NOT using a window manager at all. Yes, it can easily be seen from the comments to the question that many people think it's foolhearty or even stupid to NOT use a window manager, but in my case I made the EXACTLY right choice, and here's why:

THIS PROJECT'S circumstances are one of the rare cases for "doing it yourself", and, indeed, if I'd used a window manager it would NOT have worked out _AT_ALL!_ ...at least not in the time I had available.

A brief review of the use-case for this project

This was for dedicated hardware control and, indeed, it could not run in production in any place but a very singular installation of specialized hardware that the Java code is providing a user-interface for. Further, it won't have any internet connection, ever, and will never be upgraded. There's ZERO concern over either operating system or other software upgrade - it just cannot happen. As it has a singular fixed running environment, there's no concern over font-change handling or anything like that.

The Application Design; WHY A Layout Manager Would Screw It Up

I chose to use one frame, "undecorated" so that if fills the entire display, like this:

This fills a 1090 X 1920 display completely, so IDK how well it will go here.

I created a JFrame that serves as a backdrop for the whole thing. Within it, I first created a menu bar, followed by a heading / title bar, and for these things, a layout manager could have done a great job, of course, but that's the end of the easy part.

I created a right and left column of necessarily different widths and then a section at the bottom just by placing the items using item.setBounds(X, Y, W, H) . I used variables for the values, and used them to create standard row & column positions, widths and heights. This provided for easy shifting from the standard in places that required it; I'd just use a different set of variables (using a naming convention I invented to keep it easy). I'd imagine that you COULD have used a layout manager for this part, but it would have been tedious and it's not at all clear it would have been any less work. In particular, how do you get the two vertical columns do be where you want them? You'd have to create separate inset panes / panels for each differently formatted region within each column - and even the bottom rows! You'd have to get them to stack or space just right, too. Then there are those vertical and horizontal bars - how'd you do that?

Vitally, I left room for an inset panel in the center, of which there are a VERY large number (!!) way more than are apparent from what you can see in the sample image. They're JPanels , only one of which is visible here, of course. And this is where a layout manager would completely fall on its face. Good UI design keeps things consistent and so users can know where to expect to find various things. And on the various panels, there are things that are common among some panels and different on others with DIFFERENT commonality, and there are yet more panels that cross with commonality between different sets of panes, yet few of the panels are really full enough that the common layout manager packing algorithms could handle; Various items are - and need to be - in what may appear to be non-standard positions for various reasons, so using a layout manager would have required filling up the panes with lots of sub-panels and such so that each of the various layout managers could do their jobs properly. By NOT using a layout manager, and thereby being free to just exactly specify the different positioning of the components when looking at different inset panes, I was able to VERY SIMPLY just use panel.add(item) syntax to move items between panes and keep the position exactly. Further, because of the same top position of the outer panel and the inner ones, getting rows exactly right was a cinch!

This was hands-down the easiest approach. I would have been fighting the damned layout manager all along the way. ...DO NOT BE AFRAID TO SKIP A LAYOUT MANAGER AND DO IT YOURSELF, just be prepared to do the whole job yourself. If you're up to that task, and if you have a fixed-use-case situation like I had, it's not so bad at all, and it might even be the only practical way for some tasks.