定义数据类型：class interface byte short int long flost double char boolean
定义流程控制：if else switch case default while do for break continue retum
定义访问权限修饰符：private protected public
定义类，函数，变量修饰符：abstract final static synchronized
定义类与类之间关系：extends implements
定义建立实例，引用实例，判断实例：new this super instanceof
用于异常处理；try catch finally throw throws
其它修饰符：native strictfp transient volatile asseit
