急:java使用皮肤包

我下载了几个java的皮肤,zip类型的文件也有jar类型的文件,但不知道怎么在java应用程序中去加载它们里面的皮肤(xml、class),我的原代码为:
import java.awt.Toolkit;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import java.awt.Dimension;
import java.awt.*;
import javax.swing.plaf.synth.*;

public class Application1 {
boolean packFrame = false;

public Application1() {
Frame1 frame = new Frame1();
if (packFrame) {
frame.pack();
} else {
frame.validate();
}

// Center the window
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
Dimension frameSize = frame.getSize();
if (frameSize.height > screenSize.height) {
frameSize.height = screenSize.height;
}
if (frameSize.width > screenSize.width) {
frameSize.width = screenSize.width;
}