Syntax for command line arguments in Java - Step-by-Step Execution

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Concept Flow - Syntax for command line arguments

Start Program

↓

Read args array

↓

Check args length

Yes No↓

Use args

↓

Process args

↓

End Program

The program starts and reads the command line arguments from the args array, checks if arguments exist, then processes them or handles no arguments.

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Execution Sample

Java

public class Main {
  public static void main(String[] args) {
    if (args.length > 0) {
      System.out.println("First arg: " + args[0]);
    } else {
      System.out.println("No arguments passed.");
    }
  }
}

Prints the first command line argument passed to the program, or a message if no arguments are passed.

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Execution Table

Step	Action	args array content	Output	Notes
1	Program starts	args = ["hello", "world"]		args array filled with command line inputs
2	Access args[0]	["hello", "world"]		First argument is "hello"
3	Print args[0]	["hello", "world"]	First arg: hello	Output to console
4	Program ends	["hello", "world"]		Program finishes execution

💡 Program ends after printing the first argument.

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Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
args	empty	["hello", "world"]	["hello", "world"]	["hello", "world"]	["hello", "world"]

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Key Moments - 2 Insights

▶Why do we use args[0] to get the first command line argument?

▶What happens if no command line arguments are passed?

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Visual Quiz - 3 Questions

Look at the execution_table, what is printed at step 3?

A First arg: hello

B First arg: world

C First arg: args[0]

D No output

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Concept Snapshot

Java command line arguments are passed as a String array named args to main.
Access arguments by index: args[0], args[1], etc.
Always check args.length before accessing to avoid errors.
Example: public static void main(String[] args) { if (args.length > 0) { System.out.println(args[0]); } else { System.out.println("No arguments passed."); } }

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Full Transcript

In Java, command line arguments are given to the main method as a String array called args. The program starts and the args array contains the arguments typed after the program name. We access the first argument with args[0]. If no arguments are passed, args is empty, so we must check args.length before accessing to avoid errors. The example program prints the first argument or a message if none are passed. The execution steps show the program starting, reading args, printing the first argument, then ending.