double m = 78.5;
//将基本类型转换为字符串
String str1 = Double.toString(m) ;
System.out.println("m 转换为String型后与整数20的求和结果为: "+(str1+20));
str1=“78.5”
str+20=“78.5”+20
String类型的加法相当于append,在后面追加,所以等于78.520