Java named command line arguments

Java Command-Line Arguments

The command-line arguments in Java allow us to pass arguments during the execution of the program.

As the name suggests arguments are passed through the command line.

Example: Command-Line Arguments

Let’s try to run this program using the command line.

1. To compile the code

2. To run the code

Now suppose we want to pass some arguments while running the program, we can pass the arguments after the class name. For example,

Here apple , ball , and cat are arguments passed to the program through the command line. Now, we will get the following output.

Command-Line arguments are Apple Ball Cat 

In the above program, the main() method includes an array of strings named args as its parameter.

public static void main(String[] args)

The String array stores all the arguments passed through the command line.

Note: Arguments are always stored as strings and always separated by white-space.

Passing Numeric Command-Line Arguments

The main() method of every Java program only accepts string arguments. Hence it is not possible to pass numeric arguments through the command line.

However, we can later convert string arguments into numeric values.

Example: Numeric Command-Line Arguments

Let’s try to run the program through the command line.

// compile the code javac Main.java // run the code java Main 11 23 

Here 11 and 23 are command-line arguments. Now, we will get the following output.

Arguments in integer form 11 23 

In the above example, notice the line

int argument = Intege.parseInt(str); 

Here, the parseInt() method of the Integer class converts the string argument into an integer.

Similarly, we can use the parseDouble() and parseFloat() method to convert the string into double and float respectively.

Note: If the arguments cannot be converted into the specified numeric value then an exception named NumberFormatException occurs.

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Command-Line Arguments

A Java application can accept any number of arguments from the command line. This allows the user to specify configuration information when the application is launched.

The user enters command-line arguments when invoking the application and specifies them after the name of the class to be run. For example, suppose a Java application called Sort sorts lines in a file. To sort the data in a file named friends.txt , a user would enter:

When an application is launched, the runtime system passes the command-line arguments to the application’s main method via an array of String s. In the previous example, the command-line arguments passed to the Sort application in an array that contains a single String : «friends.txt» .

Echoing Command-Line Arguments

The Echo example displays each of its command-line arguments on a line by itself:

The following example shows how a user might run Echo . User input is in italics.

java Echo Drink Hot Java Drink Hot Java

Note that the application displays each word — Drink , Hot , and Java — on a line by itself. This is because the space character separates command-line arguments. To have Drink , Hot , and Java interpreted as a single argument, the user would join them by enclosing them within quotation marks.

java Echo "Drink Hot Java" Drink Hot Java

Parsing Numeric Command-Line Arguments

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 :

int firstArg; if (args.length > 0) < try < firstArg = Integer.parseInt(args[0]); >catch (NumberFormatException e) < System.err.println("Argument" + args[0] + " must be an integer."); System.exit(1); >>

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 in Java

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Command Line Arguments in Java

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Command-line arguments in Java are used to pass arguments to the main program. If you look at the Java main method syntax, it accepts String array as an argument. When we pass command-line arguments, they are treated as strings and passed to the main function in the string array argument. The arguments have to be passed as space-separated values. We can pass strings and primitive data types as command-line arguments. The arguments will be converted to strings and passed into the main method string array argument.

Command Line Arguments in Java

package com.journaldev.examples; public class CommandLineArguments < public static void main(String[] args) < System.out.println("Number of Command Line Argument = "+args.length); for(int i = 0; i< args.length; i++) < System.out.println(String.format("Command Line Argument %d is %s", i, args[i])); >> > 

$ java com/journaldev/examples/CommandLineArguments.java Number of Command Line Argument = 0 

Now, let’s pass some arguments to the main class. We have to pass the arguments as space-separated values.

$ java com/journaldev/examples/CommandLineArguments.java "A" "B" "C" Number of Command Line Argument = 3 Command Line Argument 0 is A Command Line Argument 1 is B Command Line Argument 2 is C $ java com/journaldev/examples/CommandLineArguments.java 1 2 3 Number of Command Line Argument = 3 Command Line Argument 0 is 1 Command Line Argument 1 is 2 Command Line Argument 2 is 3 $ 

Note: If you are using Java 11 or higher, you don’t need to compile the java source file explicitly. The java command will compile and run the class simultaneously.

How to Pass Command Line Arguments in Eclipse

Step 1: Open the Class Run Configurations Settings

From the class editor, right click and chose “Run As” -> “Run Configurations…”.

Step 2: Specify the Program Arguments in the Arguments Tab

In the pop up window, click on the Arguments tab. Then provide the command line arguments value in the “Program Arguments” text box.

Step 3: Click on the Run button

When you will click on the Run button, the run configurations will be saved and the program will execute with the specified command-line arguments. If you run the class again, the saved run configuration will be used. So if you want to override the command-line arguments or remove them, you will have to open the run configurations window and make necessary changes.

Conclusion

The command-line arguments are used to provide values that are essential to run the program. For example, we can specify the database credentials to be used by the program. We can specify the configuration file location from where the program should pick the required values. Reference: Command-Line Arguments Oracle Docs

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