https://openjdk.java.net/ 
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 * accompanied this code).
 *
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Provides one interface and many abstract classes that Swing uses to provide its pluggable look-and-feel capabilities. Its classes are subclassed and implemented by look and feel UIs such as Basic and the Java look and feel (Metal). This package is only used by developers who cannot create a new look and feel by subclassing existing look-and-feel components (such as those provided by the javax.swing.plaf.basic and javax.swing.plaf.metal packages). 

Note:
Most of the Swing API is not thread safe. For details, see
Concurrency in Swing,
a section in
The Java Tutorial.

Since:1.2
@serialexclude
/**
 * Provides one interface and many abstract classes that Swing uses to provide
 * its pluggable look-and-feel capabilities. Its classes are subclassed and
 * implemented by look and feel UIs such as Basic and the Java look and feel
 * (Metal). This package is only used by developers who cannot create a new
 * look and feel by subclassing existing look-and-feel components (such as those
 * provided by the {@code javax.swing.plaf.basic} and
 * {@code javax.swing.plaf.metal} packages).
 * <p>
 * <strong>Note:</strong>
 * Most of the Swing API is <em>not</em> thread safe. For details, see
 * <a
 * href="http://docs.oracle.com/javase/tutorial/uiswing/concurrency/index.html"
 * target="_top">Concurrency in Swing</a>,
 * a section in
 * <em><a href="http://docs.oracle.com/javase/tutorial/"
 * target="_top">The Java Tutorial</a></em>.
 *
 * @since 1.2
 * @serial exclude
 */
package javax.swing.plaf;