First of all, the method of System.out.println () is to print the bracketed string to the console window and wrap it.

In addition, you need to know that for strings, "+"means concatenating two strings.

There are no A and B enclosed in quotation marks, which are not seemingly simple reference variables, but implicitly converted into strings (that is, calling toString () method):

"a="+a+", b="+b is actually "a = "+a.tostring ()+", b = "+b.tostring ().

So the System.out.println () method here is to print the above string in the console window.

For example:

int a = 1；

Double b =1.5;

System.out.println("a="+a+"，b = "+b)；

On the console window, it will display:

a= 1，b= 1.5