处理点击按钮事件 一个面板上放置了3个按钮，对应每个按钮有一个事件监听器，当用户点击任何一个按钮， 面板的颜色发生相应的变化。-Processing click on the button events A panel has placed three button, for each button has an event listeners, when users click on any one button, Panel color changes o