TabbedPane closable tabs

[DevCharly]

This PR introduces support for closable tabs.

Set client property JTabbedPane.tabClosable to true on a JTabbedPane to enable closing tabs.
You also have to provide a callback in client property JTabbedPane.tabCloseCallback that is responsible for closing the tab.

myTabbedPane.putClientProperty( "JTabbedPane.tabClosable", true );
myTabbedPane.putClientProperty( "JTabbedPane.tabCloseCallback",
    (java.util.function.BiConsumer<JTabbedPane, Integer>) (tabbedPane, tabIndex) -> {
        // close tab here
        tabbedPane.removeTabAt( tabIndex );
    } );

If you do not need the tabbed pane in the callback, it is possible to use a java.util.function.IntConsumer:

myTabbedPane.putClientProperty( "JTabbedPane.tabCloseCallback",
    (java.util.function.IntConsumer) tabIndex -> {
        // close tab here
        myTabbedPane.removeTabAt( tabIndex );
    } );

To show a tooltip if the mouse is over the close button, set the client property JTabbedPane.tabCloseToolTipText:

myTabbedPane.putClientProperty( "JTabbedPane.tabCloseToolTipText", "Close" );

You can set the three client properties also on single tabs. E.g. if not all tabs should be closeable. Or if only some tabs should be closable.

Component c = tabbedPane.getComponentAt( 1 );
((JComponent)c).putClientProperty( "JTabbedPane.tabClosable", false );

The style of the close button can be changed via UI properties. Here are the defaults for light themes:

TabbedPane.closeSize=16,16
TabbedPane.closeArc=4
TabbedPane.closeCrossPlainSize={float}7.5
TabbedPane.closeCrossFilledSize=$TabbedPane.closeCrossPlainSize
TabbedPane.closeCrossLineWidth={float}1

TabbedPane.closeBackground=null
TabbedPane.closeForeground=@disabledText
TabbedPane.closeHoverBackground=darken($TabbedPane.hoverColor,10%)
TabbedPane.closeHoverForeground=@foreground
TabbedPane.closePressedBackground=darken($TabbedPane.hoverColor,15%)
TabbedPane.closePressedForeground=$TabbedPane.closeHoverForeground

If you prefer circle close buttons, set arc to a large value and make filled cross smaller:

UIManager.put( "TabbedPane.closeArc", 999 );
UIManager.put( "TabbedPane.closeCrossFilledSize", 5.5f );

If you don't want a filled button on hover, but change cross color to red, try:

UIManager.put( "TabbedPane.closeHoverForeground", Color.red );
UIManager.put( "TabbedPane.closePressedForeground", Color.red );
UIManager.getLookAndFeelDefaults().put( "TabbedPane.closeHoverBackground", null );

This is part of TabbedPane improvements as discussed in issue #40 (comment) and #31.

CC @Gaarco @swordmaster2k

[Chrriis]

I tried to replace a home-made version of closable icons, so I naively removed the "close" component from the tab component and set the property instead. This did not work because I was acting on the tab component (cf. getTabComponentAt(index)) while the properties seem to have to be set on the component placed in the tab.

I think transition would be much easier if FlatLaf was also checking if a tab component is defined and read the properties from there first, then fallback on the component in the tab or the tabbed pane. What do you think?