Command Line Arguments in Java: A Comprehensive Guide

Command-Line Arguments

Sometimes we want to pass information into a program when we run it. This is accomplished by passing command-line arguments to main( ).

The main method can receive string arguments from the command line

Acommand-line argument is the information that directly follows the program’s name on the command line when it is executed.

To access the command-line arguments inside a Java program is quite easy— they are stored as strings in a String array passed to the args parameter of main( ). The first command-line argument is stored at args[0], the second at args[1], and so on.

Program

<span class="pln">
</span><span class="com">// Display all command-line arguments.</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">CmdLine</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pln"> args</span><span class="pun">[])</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
	</span><span class="kwd">for</span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun">&lt;</span><span class="pln"> args</span><span class="pun">.</span><span class="pln">length</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln">
	</span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"args["</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> i </span><span class="pun">+</span><span class="pln"> </span><span class="str">"]: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln">args</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]);</span><span class="pln">
	</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span>

Output

Process of Compilation and Execution

Microsoft Windows [Version 6.2.9200]
(c) 2012 Microsoft Corporation. All rights reserved.

C:\Users\Hello World>cd desktop

C:\Users\Hello World\Desktop>cd Java

C:\Users\Hello World\Desktop\JAVA>javac CmdLine.java

C:\Users\Hello World\Desktop\JAVA>java CmdLine This is Commend-Line Argument Example
args[0]: This
args[1]: is
args[2]: Commend-Line
args[3]: Argument
args[4]: Example

C:\Users\Hello World\Desktop\JAVA>

Perhaps we have already noticed the unusual header for the main method, which has the parameter args of String[] type. It is clear that args are an array of strings. The main method is just like a regular method with a parameter. we can call a regular method bypass- ing actual parameters. Can we pass arguments to main? Yes, of course, we can. In the fol- lowing examples, the main method in class TestMain is invoked by a method in A

Program

Save as: ClassA.java
public class ClassA {
public static void main(String[] args) {
	String[] strings = {"New York","Boston", "Atlanta"};
    TestMain.main(strings);
	}
}
 

Save as: MainMethod.java
public class  MainMethod {

	public static void main(String[] args){
    for (int i = 0; i < args.length; i++)
    System.out.println(args[i]);
   }
}

Output

Microsoft Windows [Version 6.2.9200]
(c) 2012 Microsoft Corporation. All rights reserved.

C:\Users\Hello World>cd desktop

C:\Users\Hello World\Desktop>cd java
 
C:\Users\Hello World\Desktop\JAVA>javac MainMethod.java

C:\Users\Hello World\Desktop\JAVA>java MainMethod if you succeed in cheating someone, dont't think that the pe
rson is a Fool
if
you
succeed
in
cheating
someone,
dont't
think
that
the
person
is
a
Fool