The javax.swing.UIManager class, where the appearance is set, is a singleton. Only one can be installed at any given time.
However, you can (if you are so inclined) override UI delegates for individual components (see JComponent.setUI () ). Using this method, you could probably hack some of the components that the delegates of the user interface of an alternative view and feelings use. But in most cases, they will look for UIDefaults set by the "real" appearance, so, at best, it will be a bad approximation.
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