可以直接相加，相加之后都變成double類型。自動轉換按從低到高的順序轉換。如下：

????低--------------------------------------------->高
????byte,short,char->?int?->?long?->?float?->?double

public?class?Demo?{
????public?static?void?main(String[]?args){
????????double?avg1=78.5;//雙精度形
????????int?rise=5;//整形
?????????double?avg2=avg1+rise;??//?提高精度
????????System.out.println("avg2?=?"?+?avg2);
???}
}