System.out refers to the out field of the System class. System.out.println refers to the println method of that field. A method body is made up of statements. These include method calls, assignments, and flow control. HelloWorld has an example of a statement which is a method call.
Many statements end in a semicolon.
Here expr may be any expression. An expression may be a method call, a variable, or any combination of these with the operators. Flow Control Flow control includes if , for , and while . Above is a typical if statement. The else portion is optional.