Command line-arguments-in-java-tutorial

Command line-arguments-in-java-tutorial

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  Command-line Arguments in Java
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  Objectives At the endof the lesson, the student should be able to: Know and explain what a command-line argument is Get input from the user using command-line arguments How to pass command-line arguments in Command prompt
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  Command-line Arguments • Commandline arguments means a way to pass parameters to the main function while executing the program. • A Java application can accept any number of arguments from the command-line. • Command-line arguments allow the user to affect the operation of an application. • The user enters command-line arguments when invoking the application and specifies them after the name of the class to run.
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  Command-line Arguments • Forexample, suppose you have a Java application, called Sort, that sorts five numbers, you run it like this: ● Note: The arguments are separated by spaces.
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  Command line argumentsin DOS • The following screen image shows Command line arguments in DOS:
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  How Java ApplicationReceive Command-line Arguments • In Java, when you invoke an application, the runtime system passes the command-line arguments to the application‘s main method via an array of Strings. public static void main( String[] args ) • Each String in the array contains one of the command-line arguments.
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  args[ ] array •Given the previous example where we run: java Sort 5 4 3 2 1 • the arguments are stored in the args array of the main method declaration as…
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  Example To print thearray of arguments, we write: 1 public class CommandLineSample 2 { 3 public static void main( String[] args ){ 4 5 for(int i=0; i<args.length; i++){ 6 System.out.println( args[i] ); 7 } 8 9 } 10 }
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  Conversion of Command-lineArguments • If your program needs to support a numeric command-line argument, it must convert a String argument that represents a number, such as "34", to a number. • Here's a code snippet that converts a command- line argument to an integer, int firstArg = 0; if (args.length > 0){ firstArg = Integer.parseInt(args[0]); } the parseInt() method in the Integer class throws a NumberFormatException (ERROR) if the format of args[0] isn't valid (not a number).
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  Parsing Numeric Command-LineArguments with exception handling • If an application needs to support a numeric command-line argument, it must convert a String argument that represents a number, such as "34", to a numeric value. Here is a code snippet that converts a command-line argument to an int: parseInt throws a NumberFormatException if the format of args[0] isn't valid. All of the Number classes — Integer, Float, Double, and so on — have parseXXX methods that convert a String representing a number to an object of their type.
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  Command-line Arguments: Coding Guidelines •Before using command-line arguments, always check the number of arguments before accessing the array elements so that there will be no exception generated. • For example, if your program needs the user to input 5 arguments,
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  Examples • The codesnippet shows the switch method working through command line arguments…
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  Compiling and executingSwitch.java
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  Another example…
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  Summary Command-line arguments – Howto access the arguments – How to convert String arguments to integer using Integer.parseInt method – How to pass command-line arguments in Command prompt