Java Lesson 16: Handling of null

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The main class looks as follows: 

public class MyClass {
    public static void main(String[] args) {
        Argument argument1 = ArgumentHelper.getArgument(0,args);
        Argument argument2 = ArgumentHelper.getArgument(1,args);
        printStuff(argument1);
        printStuff(argument2);
    }
 
    public static void printStuff(Argument data) {
        System.out.println("You specified: "+data.getValue());
    }
 
}

The helper class looks as follows: 

public class ArgumentHelper {
    public static Argument getArgument(int argumentNumber, String[] args) {
        if(args.length>argumentNumber) {
            int argument = 0;
            try {
                argument = Integer.valueOf(args[argumentNumber]);
                // If we end up here it has successfully converted the parameter to an integer
                return new IntArgument(argument);
 
            } catch (NumberFormatException e) {
                // If we end up here the parameter could not be converted to an integer and
                StringArgument strArgument = new StringArgument();
                strArgument.setString(args[argumentNumber]);
                return strArgument;
            }
        }else {
            return null;
        }
    }
}

The Argument looks as follows: 

public abstract class Argument {
    public abstract String getValue();
}

The IntArgument looks as follows: 

public class IntArgument extends Argument {
    private int intArgument;
    public IntArgument(int intArgument) {
        this.intArgument = intArgument;
    }
    public int getInt() {
        return intArgument;
    }
    public String getValue() {
        return String.valueOf(intArgument);
    }
}

The StringArgument looks as follows: 

public class StringArgument extends Argument {
    private String strArgument;
    public void setString(String arg) {
        this.strArgument = arg;
    }
    public String getString() {
        return strArgument;
    }
    public String getValue() {
        return String.valueOf(strArgument);
    }
}

Your work is to update the main method in the main class so it can be executed as: 

java MyClass 5

And give the output like: 

You specified: 5

But it should also be possible to execute the program as: 

java MyClass 5 Hello

And then it should give the output like: 

You specified: 5
You specified: Hello

You are not allowed to have a if-statement in the main method that checks if args.length<2, the if-statement is only allowed to look at the return value from ArgumentHelper. Look in the ArgumentHelper code to see what it returns if the arguments could not be retrieved.

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