动态地改变程序的Look and Feel,由于JFrame、JApplet等为重量级组件，因此它的外观只与操作系统平台有关系，在相同的操作系统平台下表现出相同的外观。-Dynamically change the program s Look and Feel, due JFrame, JApplet as the heavyweight component, so it looks just a relationship with the operating system platform, under the same operating system platforms exhibit the same appearance.