GEF:Tool的职责

1.通知EditPart显示和隐藏FeedBack

2.从EditPart中获取Command(当然，EditPart又会从EditPolicy去取Command)

3.在命令堆栈里执行Command。
AbstractTool里面的代码
/**
 * Executes the given command on the command stack.
 * @since 3.1
 * @param command the command to execute
 */
protected void executeCommand(Command command) {
 getDomain().getCommandStack().removeCommandStackEventListener

(commandStackListener);
 try {
  getDomain().getCommandStack()
   .execute(command);
 } finally {
  getDomain().getCommandStack().addCommandStackEventListener

(commandStackListener);
 }
}

4.更新鼠标光标