Java - When there is no user input prevent an error message - Homework

Question

The program is supposed to take a string input by the user and return it reversed. (ex "Hello" is input "olleH" is the output.) You do this by running the program like java ReverseCL2 Hello However, when no string is input with it, it prints an ArrayOutOfIndexException. I need it to instead print out what the user is supposed to do (Please input a string when running the code.) I have tried what is below and also if (args[0].equals(null)). Thanks in advance for any help :)

public class ReverseCL2
{
    public static void main(String[] args)
    {
        String s = args[0];
        String rev = "";
        if (args[0].isEmpty())
        {
            System.out.println("Input a string to be reversed");
        }
        else
        {
            for (int i=0; i<s.length(); i++) 
            {
                rev = s.charAt(i) + rev;
            }
            System.out.println(rev);
        }

    } 
}

Stuart Golodetz · Accepted Answer · 2013-11-01 13:34:07Z

1

Check for args.length being zero first, i.e.

if(args.length == 0 || args[0].isEmpty())
{
    // <Handle special case however you like>
}

The ArrayIndexOutOfBoundsException you get is a result of trying to access args[0] when args has size 0.

edited Nov 1, 2013 at 13:34

answered Nov 1, 2013 at 10:46

Stuart Golodetz

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Comments

Michele Mariotti · Accepted Answer · 2013-11-01 10:47:43Z

1

public class ReverseCL2
{
    public static void main(String[] args)
    {
        if(args.length == 0 || args[0].isEmpty())
        {
            System.out.println("Input a string to be reversed");
            return;
        }

        String s = args[0];
        String rev = "";

        for(int i = 0; i < s.length(); i++) 
        {
            rev = s.charAt(i) + rev;
        }

        System.out.println(rev);

    } 
}

answered Nov 1, 2013 at 10:47

Michele Mariotti

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3 Comments

Stuart Golodetz Over a year ago

+1: Fair point - you (i.e. the OP) still need to check for it then being empty as well.

Michele Mariotti Over a year ago

if(args.length == 0 || args[0].isEmpty()) checks for empty array and empty value... this code is absolutely correct. (and this is really a basic problem)

Stuart Golodetz Over a year ago

Yes, I know - I was observing that I answered the question too quickly and just showed how to avoid the exception whilst stupidly forgetting the second part of the condition. Hence the upvote I gave you, and the fact that I then corrected myself :)

KhAn SaAb · Accepted Answer · 2013-11-01 10:47:05Z

0

put ! for checking the parameterized array value

if (!args[0].isEmpty() && args.length==0)

See above line in your code.

    public class ReverseCL2
{
    public static void main(String[] args)
    {
        String s = args[0];
        String rev = "";
        if (!args[0].isEmpty() && args.length==0)
        {
            System.out.println("Input a string to be reversed");
        }
        else
        {
            for (int i=0; i<s.length(); i++) 
            {
                rev = s.charAt(i) + rev;
            }
            System.out.println(rev);
        }

    } 
}

answered Nov 1, 2013 at 10:47

KhAn SaAb

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Comments

sravan · Accepted Answer · 2013-11-01 10:47:54Z

0

It simple arg0 is array so before get data from That check Array size 


if(args.length == 0)
{
    // <Show message to user >
}else{

// <write here Working code >

}

answered Nov 1, 2013 at 10:47

sravan

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Comments

Aniket Thakur · Accepted Answer · 2013-11-01 11:00:01Z

0

In addition to above answers a more simpler code(reading vise) would be

public static void main(String args[]) {

    switch (args.length) {

        case 0 : System.out.println("Input a string to be reversed");
            break;
        default:    //your logic

    }
}

answered Nov 1, 2013 at 11:00

Aniket Thakur

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2 Comments

Stuart Golodetz Over a year ago

This unfortunately doesn't do an empty check on args[0] when args.length != 0.

Aniket Thakur Over a year ago

That logic would come in the default case(Non zero arguments). You can always check for empty or null before processing the data.

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