Java Reference
In-Depth Information
mentthatreturnsavalueofthistype(e.g., return 0; ),thecompilerwillnot
reportanerror.However,youwon'tbeabletorun HelloWorld becausethe
proper main() method would not exist.
(String[] args) :Thisparameterlistconsistsofasingleparameternamed
args oftype String[] .Startupcodepassesasequenceofcommand-linear-
gumentsto args ,whichmakestheseargumentsavailabletothecodethatex-
ecuteswithin main() .You'lllearnaboutparametersandargumentsin Chapter
2 .
The block of code consists of a single System.out.println("Hello,
world!"); methodcall.Fromlefttowrite, System identifiesastandardclassofsys-
tem utilities, out identifies an object variable located in System whose methods let
you output values of various types optionally followed by a newline character to the
standardoutputdevice, println identifiesamethodthatprintsitsargumentfollowed
byanewlinecharactertostandardoutput,and "Hello, world!" isa string (ase-
quenceofcharactersdelimitedbydoublequote " charactersandtreatedasaunit)thatis
passedastheargumentto println andwrittentostandardoutput(thestarting " and
ending " double quote characters are not written; these characters delimit but are not
part of the string).
Note AlldesktopJava/nonJavaapplicationscanberunatthecommandline.Before
graphical user interfaces with their controls for inputting and outputting values (e.g.,
textfields), these applications obtained their input and generated their output with the
help of Standard I/O , an input/output mechanism that originated with the Unix oper-
The user would input data via the standard input device (typically the keyboard, but
a file could be specified instead—Unix treats everything as files). The application's
output would appear on the standard output device (typically a computer screen, but
optionally a file or printer). Output messages denoting errors would be output to the
Now that you understand how Listing 1-1 works, you'll want to create this applica-
tion. Complete the following steps to accomplish this task:
1. Copy Listing 1-1 to a file named .
2. Execute javac tocompilethissourcefile. javac will
complain if you do not specify the “ .java ” file extension.
Search WWH ::

Custom Search