java中的关键字全为小写
用于类接口声明：class interface extends implements 包引入和包声明：import package 数据类型: byte int short long float double char boolean 某些数据类型的可先值：false true null 流程控制：break continue return for do while if else switch case default 异常处理：try catch finally throw throws 修饰符：private protected public abstract final static native synchronized transient volatile 操作符：instanceof 创建对象：new 引用：this super 方法返回类型：void
