int 最大值21亿多，默认值0，integer 默认值null
short 最大值32768
short = (short)int //需要强转
int = short; //不需要强转
int + short = int
int == Integer //true
Integer==Integer // Integer<128:true Integer>128:false
short + short = int 会转为Int操作，结果为int
short += 1 正确，会隐式强制， short = short+1报错