What is String args parameter in main method Java

Question

I m just beginning to write programs in Java  What does the following Java code mean   public static void main String   args     What is String   args   When would you use these args    Source code and or examples are preferred over abstract explanations

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When you finish your code  you will turn it into a file with the extension  java  which can be run by double clicking it  but  also throughout a console  terminal on a mac  cmd exe on windows  which lets the user do many things  One thing is they can see console messages  System out print or System out println  which they can t see if they double click  Another thing they can do is specify parameters  so normally you would use the line   java -jar MyCode jar   after navigating to the folder of the program with   cd C My Code Location   on windows or  cd My Code Location   on Mac  notice that mac is less clunky  to run code  but to specify parameters you would use  java -jar MyCode jar parameter1 parameter2   These parameters stored in the args array  which you can use in your program is you want to allow the user to control special parameters such as what file to use or how much memory the program can have  If you want to know how to use an array  you could probably find a topic on this site or just google it  Note that any number of parameters can be used

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The String   args parameter is an array of Strings passed as parameters when you are running your application through command line in the OS   So  imagine you have compiled and packaged a myApp jar Java application  You can run your app by double clicking it in the OS  of course  but you could also run it using command line way  like  in Linux  for example    user computer    java -jar myApp jar   When you call your application passing some parameters  like   user computer    java -jar myApp jar update notify   The java -jar command will pass your Strings update and notify to your public static void main   method   You can then do something like   System out println args 0      Which will print  update  System out println args 1      Which will print  notify

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args contains the command-line arguments passed to the Java program upon invocation  For example  if I invoke the program like so     java MyProg -f file txt   Then args will be an array containing the strings  -f  and  file txt

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try this  System getProperties   getProperty  quot sun java command quot        System getProperties   getProperty  quot sun rt javaCommand quot

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The style dataType   arrayRefVar is preferred  The style dataType arrayRefVar   comes from the C C   language and was adopted in Java to accommodate C C   programmers

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in  public static void main String args    args is an array of console line argument whose data type is String  in this array  you can store various string arguments by invoking them at the command line as shown below  java myProgram Shaan Royal then Shaan and Royal will be stored in the array as arg 0   Shaan   arg 1   Royal   you can do this manually also inside the program  when you don t call them at the command line

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Even tho OP is only talking about the String   args  i want to give a complete example of the public static void main String   args     Public   is an Access Modifier  which defines who can access this Method  Public means that this Method will be accessible by any Class If other Classes are able to access this Class     Static   is a keyword which identifies the class related thing  This means the given Method or variable is not instance related but Class related  It can be accessed without creating the instance of a Class   Void   is used to define the Return Type of the Method  It defines what the method can return  Void means the Method will not return any value   main  is the name of the Method  This Method name is searched by JVM as a starting point for an application with a particular signature only   String   args   is the parameter to the main Method   If you look into JDK source code  jdk-src j2se src share bin java c       Get the application s main method    mainID     env - gt GetStaticMethodID env  mainClass   main                         Ljava lang String  V                Make sure the main method is public        mods     env - gt CallIntMethod env  obj  mid   if   mods  amp  1     0       if   Modifier isPublic mods              message    Main method not public        messageDest   JNI TRUE      goto leave        You can see that the starting method in java must be named main and must have the specific signature public static void main String   args   The code also tells us that the public static void main String   args  is not fixed  if you change the code in  jdk-src j2se src share bin java c  to another signature  it will work but changing this will give you other possible problems because of the java specs  Offtopic  It s been 7 years since OP asked this question  my guess is that OP can answer his own question by now

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The following answer is based my understanding  amp  some test   What is String   args   Ans-    String    -   As We know this is a simple String array   args  -   is the name of an array it can be anything  e g  a  ar  argument  param  parameter  no issues with compiler  amp  executed  amp  I tested as well   E g  1 public static void main String   argument   2 public static void main String   parameter   When would you use these args   Ans-   The main function is designed very intelligently by developers  Actual thinking is very deep      Which is basically developed under consideration of C  amp  C   based on Command line argument but nowadays nobody uses it more    Thing 1- User can enter any type of data from the command line can be Number or String  amp  necessary to accept it by the compiler which datatype we should have to use  see the thing 2  Thing 2- String is the datatype which supports all of the primitive datatypes like int  long  float  double  byte  shot  char in Java  You can easily parse it in any primitive datatype   E g The following program is compiled  amp  executed  amp  I tested as well   If input is -   1  1      one class needs to have a main   method public class HelloWorld        arguments are passed using the text field below this editor   public static void main String   parameter          System out println parameter 0    parameter 1       Output is 11    Comment out below code in case of String     System out println Integer parseInt parameter 0     Integer parseInt parameter 1       Output is 2     System out println Float parseFloat parameter 0     Float parseFloat parameter 1       Output is 2 0         System out println Long parseLong parameter 0     Long parseLong parameter 1       Output is 2         System out println Double parseDouble parameter 0     Double parseDouble parameter 1       Output is 2 0

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I think it s pretty well covered by the answers above that String args   is simply an array of string arguments you can pass to your application when you run it  For completion  I might add that it s also valid to define the method parameter passed to the main method as a variable argument  varargs  of type String   public static void main  String    args   In other words  the main method must accept either a String array  String args    or varargs  String    args  as a method argument  And there is no magic with the name args either  You might as well write arguments or even freddiefujiwara as shown in below e gs    public static void main  String   arguments   public static void main  String   freddiefujiwara

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String   args means an array of sequence of characters  Strings  that are passed to the  quot main quot  function  This happens when a program is executed  Example when you execute a Java program via the command line  java MyProgram This is just a test Therefore  the array will store    quot This quot    quot is quot    quot just quot    quot a quot    quot test quot

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In addition to all the previous comments   public static void main String   args     can be written as    public static void main String   arg    or   public static void main String   strings

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In Java args contains the supplied command-line arguments as an array of String objects   In other words  if you run your program as java MyProgram one two then args will contain   one    two     If you wanted to output the contents of args  you can just loop through them like this     public class ArgumentExample       public static void main String   args            for int i   0  i  lt  args length  i                  System out println args i

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Those are for command-line arguments in Java  In other words  if you run  java MyProgram one two  Then args contains     quot one quot    quot two quot    public static void main String    args        String one   args 0        quot one quot      String two   args 1        quot two quot     The reason for this is to configure your application to run a particular way or provide it with some piece of information it needs   If you are new to Java  I highly recommend reading through the official Oracle s Java    Tutorials

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String    args is also how you declare an array of Strings in Java     In this method signature  the array args will be filled with values when the method is called  as the other examples here show    Since you re learning though  it s worth understanding that this args array is just like if you created one yourself in a method  as in this   public void foo         String    args   new String 2       args 0     hello       args 1     every        System out println  Output      args 0    args 1            etc    the usage of  args  here and in the main method is identical

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When a java class is executed from the console  the main method is what is called   In order for this to happen  the definition of this main method must be public static void main String      The fact that this string array is called args is a standard convention  but not strictly required   You would populate this array at the command line when you invoke your program java MyClass a b c  These are commonly used to define options of your program  for example files to write to or read from

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I would break up  public static void main String args      in parts    public  means that main   can be called from anywhere    static  means that main   doesn t belong to a specific object   void  means that main   returns no value   main  is the name of a function  main   is special because it is the start of the program    String    means an array of String    args  is the name of the String    within the body of main      args  is not special  you could name it anything else and the program would work the same    String   args is a collection of Strings  separated by a space  which can be typed into the program on the terminal  More times than not  the beginner isn t going to use this variable  but it s always there just in case

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Explanation in simple layman s language   The main method expects us to provide some arguments when we direct our JVM to the class name  That means  suppose your file name is Try java  now to execute this in command prompt you write  javac Try java  to compile followed by  java Try  to execute  Now suppose instead of writing simply  java Try  you write  java Try 1   Here you have passed an argument  1   This will be taken by your main method even if you don t use it in your code   If you want to check whether your main method has actually taken the argument  1  or not  Simply  inside your main method type the following   for int i   0  i  lt  args length  i              System out println  Argument is    args i

[java] What is "String args[]"? parameter in main method Java

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