Java Check if command line arguments are null

Question

I am looking to do some error checking for my command line arguments  public static void main String   args        if args 0     null                System out println  Proper Usage is  java program filename            System exit 0             However  this returns an array out of bounds exception  which makes sense   I am just looking for the proper usage

User · Answer

To expand upon this point   It is possible that the args variable itself will be null  but not via normal execution   Normal execution will use java exe as the entry point from the command line   However  I have seen some programs that use compiled C   code with JNI to use the jvm dll  bypassing the java exe entirely   In this case  it is possible to pass NULL to the main method  in which case args will be null   I recommend always checking if   args    null      args length    0    or if   args    null   amp  amp   args length  gt  0   depending on your need

User · Answer

if i want to check if any speicfic position of command line arguement is passed or not then how to check  like for example in some scenarios 2 command line args will be passed and in some only one will be passed then how do it check wheather the specfic commnad line is passed or not  public class check    public static void main String   args    if args 0  length    0    System out println  quot entered first if quot      if args 0  length    0  amp  amp  args 1  length    0    System out println  quot entered second if quot           So in the above code if args 1  is not passed then i get java lang ArrayIndexOutOfBoundsException  so how do i tackle this where i can check if second arguement is passed or not and if passed then enter it  need assistance asap

User · Answer

jjnguy s answer is correct in most circumstances   You won t ever see a null String in the argument array  or a null array  if main is called by running the application is run from the command line in the normal way     However  if some other part of the application calls a main method  it is conceivable that it might pass a null argument or null argument array   However 2   this is clearly a highly unusual use-case  and it is an egregious violation of the implied contract for a main entry-point method   Therefore  I don t think you should bother checking for null argument values in main   In the unlikely event that they do occur  it is acceptable for the calling code to get a NullPointerException   After all  it is a bug in the caller to violate the contract

User · Answer

You should check for  args    null    args length    0   Although the null check isn t really needed  it is a good practice

User · Answer

The arguments can never be null   They just wont exist   In other words  what you need to do is check the length of your arguments   public static void main String   args           Check how many arguments were passed in     if args length    0                System out println  Proper Usage is  java program filename            System exit 0

User · Answer

If you don t pass any argument then even in that case args gets initialized but without any item element  Try the following one  you will get the same effect     public static void main String   args  throws InterruptedException           String    dummy  new String                if dummy 0     null                        System out println  Proper Usage is  java program filename                System exit 0

[java] Java: Check if command line arguments are null

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