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Java Swing How can I create a Color Swatch in my custom ColorChooserPanel?

I'm working on my custom ColorChooserPanel class, but I don't know how to create a ColorSwatch.
I found a class named ColorSwatch or something like that but its package private and I can't access it.
How can I ensure that I have a proper color chooser?

First, you need to think about the way this should work, to formulate your goals into action points that you can always check and see whether and how they are fulfilled:
it should be displayed
it should handle click events
it should be able to return a color (the last chosen color, or a default in lack of that)
Now, a very common way of supporting color choosers is to have something like in this image:
However, this is way too complex for a first implementation. You should first have something which "works", that is, you are able to choose colors to taste success and then work out the subsequent details. Unless you say otherwise, I'm assuming that the Basic colors section is good for now. In that case, you can create a class, which contains a JPanel, containing clickable elements. Your class needs to have a Color member, which one can get calling a getter and which is set when a clickable item inside your JPanel is clicked. The clickable items can be JPanels on their own, for example.
If you prefer something ready-made, then kindly read these:
https://docs.oracle.com/javase/tutorial/uiswing/components/colorchooser.html
https://coderanch.com/t/332515/java/Color-Palette

How to set a different Look & Feel for a JTable?

Is it possible to set different L&F to specific component (in my case JTable) than is already used? If so, how to do it?
Edit: I wrote this piece of code according to this tutorial. Why is this code not working? No fails or exceptions, but JTable is still the same.
NimbusLookAndFeel nb = new NimbusLookAndFeel();
jTable1.putClientProperty("Windows.Overrides",nb.getDefaults());
jTable1.putClientProperty("Windows.Overrides.InheritDefaults",false);

You can refer the below URL for all UI default values for nimbus look and feel
http://jasperpotts.com/blogfiles/nimbusdefaults/nimbus.html
Go to Table section and use all the those Table component specific UI default values in your application. That should do the trick for you.

If you would like to apply the Nimbus L&F to a button, then you simply need to figure out which class that is responsible for rendering Nimbus buttons. The process is just the same as if you want to apply your very own custom L&F, where you set your own UI class on the button.

One trick you could do is create a dummy application that uses the Nimbus look and feel, create a JTable, and do something like
System.out.println (myTable.getUI ().getClass ().getName ());
At that point you will know which UI object is used to render the JTable when using the Nimbus LAF. You can use this class name when calling setUI (TableUI) on your JTable:
myTable.setUI (new ui_manager_class_name ());
As others have said, this is hardly something we recommend though. LAF's are usually meant to be used as a whole package rather than a mix of 2-3 LAF's. Your other way out could be to use the MultiLookAndFeel, but I have never used it, so I'm not sure it does fulfill your needs. You should read the associated tutorial if you want to use it correctly.

Is it possible to remove the little dropdown arrow in a JInternalFrame?

I'm using a JInternalFrame and I want to remove the dropdown in the upper left of the frame, as it serves no purpose (I've disabled resizeable, closable, etc.)
I don't see a property for this, and I don't want to remove the entire title bar, as the title is necessary. I've looked around online, and basically come up empty here. I'm hoping it's something simple that I've just overlooked, as this is my first time using JInternalFrame, and I'm not exactly a GUI kind of guy to begin with.

internalframe.setFrameIcon(null);
Edit: hack to remove system menu in Windows:
BasicInternalFrameUI ui = (BasicInternalFrameUI)internalFrame.getUI();
Container north = (Container)ui.getNorthPane();
north.remove(0);
north.validate();
north.repaint();

The relevant Icon in The Synth Look and Feel, among the Nimbus Defaults, appears to have this key:
InternalFrame:InternalFrameTitlePane:"InternalFrameTitlePane.menuButton".icon
You may be able to use the approach shown in A Synth Example to replace the Icon.

setFrameIcon(anyBigImageThatCantBeDisplayed);
I´ve tried null parameter and got some visual issues...
So i added a big image(no background) that was already on my resource folder and the icon was no longer displayed as the menu...

How to make button highlighted or pale in java swing properly?

I'm using Swing with default UI (without any special skins).
How to make some buttons/textfields more bright or more pale? It means the user is expected/not expected(although not completely disabled) to press the button.
Example: user had changed a field - "save" button becomes more bright (for example, green). Status is "compilation failed" - "execute" button is pale (although user can still execute previous version of something). User filled in "password" field - he expected to fill in "password confirmation" - so it becomes bright.
I have: {normal, disabled, invisible}
I want: {bright, normal, pale, disabled, invisibe}.
How to make it properly, without hacking with drawing things, with separation of content and presentation? I want it to look well even if user overridden colour settings in the system. Should I use some other toolkit?
I expect something like I set hints for the given control, and then skin read hints and applies additional look and feel options (such as brighter background) without me dealing with concrete colours. May be one skin will use other background and some other skin will use other font for this effect. Like in enabled/disabled case, but more flexible.

Just use setBackground() to change the color to match the component's status. Maybe even create a Custom Component that has a method to change the status and it knowns which color matches that status.

I'm not sure that I see the value in what you're trying to achieve from the examples that you've provided. Is it possible that users could get confused about how the application works if you give them functionality that differs from their expected user experience?
If the user hasn't yet changed a field, the save button could be completely disabled. What's the value in being able to save if there have been no changes made. Alternatively, if you still dead set on making this distinction, can you do it in another way? Perhaps a visual queue, an icon next to the field that's changed, cell highlighting, or a * appended to the end of the text on the window name to show that there are unsaved changes in a window, perhaps?
From a purely user experience perspective, I don't think you want to go messing with the way people expect applications to behave unless you have a really good reason!

Reset/remove a border in Swing

Here's a very specific coding question:
I've recently been asked to maintain some old-ish Java Swing GUI code at work and ran into this problem:
I've attached my own subclass of InputVerifier called MyFilenameVerifier to a JTextField (but it may as well be any JComponent for these purposes). I've overridden the verify() method such that it calls super.verify(input) (where input is the JComponent parameter to verify()). If super.verify(input) comes back false, I do:
input.setBorder(BorderFactory.createLineBorder(Color.RED));
This is a convention used throughout the UI of this application that started long before me, so I don't have a lot of choice as far as using other ways to get the users attention (wish I did). This is just the way it works.
Problem is, once the user goes back and types something valid into the text field, I need a way to set it back to default border (instead of just saying set it to Color.GRAY or whatever, which is a different color from its original border). I need a way to say, "remove the extra decoration and go back to normal" or just set the border to its default, in other words.

Couldn't you just call input.getBorder() and cache it somewhere before setting the border to red?

Or without caching anything, you could tell the JComponent to update its UI back to the look and feel's defaults via component.updateUI. That should make the component reset its colors, borders, fonts, etc to match the original settings.

input.getBorder()
Wouldn't it be awesome if no one ever saw this and I got away free without the ass-beating I deserve for asking this question?

Not sure how your system is build, but I think you can store the original border before changing it. So you can change it back later
// assuming the Border was not null before
if (!super.verify(input)) {
original = input.getBorder();
input.setBorder(...);
} else {
if (original != null) {
input.setBorder(original);
original = null; // not needed
}
}

You need to preserve the existing border when you change it.
One way to do this is to use the methods putClientProperty() and getClientProperty(), which you'll find documented in the API.

Another possibility, if there are only a few input widgets you need this for is to subclass, e.g. JTextField, add setBorderOverride() and modify getBorder() to return "overriddingBorder" if it is not null.
Then you just use setBorderOverride(redBorder) to make it red and setBorderOverride(null) to clear it.
This of course depends on the painting to use getBorder(), which it may or may not do, and which may be implementation specific.

Incidentally, you only need a single static reference to the border-- it's the selfsame border instance used by all JTextFields.