12+3是int。只不过print方法用String.valueOf把int转成了string
看API:
print
public void print(int i)
Prints an integer. The string produced by String.valueOf(int) is translated into bytes according to the platform's default character encoding, and these bytes are written in exactly the manner of the write(int) method.
Parameters:
i - The int to be printed
See Also:
Integer.toString(int)