How to create a Java object from a string representation at runtime

Question

Eg if I have a string "{1,2,3,4,5}" I would like to get an int[] object from that string.

I have looked a bit at Janino and Beanshell, but can't seem to find the correct way to get them to do this for me.

I am looking for a generic solution, one that works for all types - not only integer arrays.

Just a normal Java string containing something like "{1,2,3}", "1", "Stackoverflow" and so forth. — Mellson, Jun 18 '12 at 10:37
That's a *different* question, since now you're asking about converting an essentially arbitrary string into, apparently, arbitrary Java objects. What are you really trying to do? — Dave Newton, Jun 18 '12 at 10:38
I am trying to create objects based on what a user types in a field. So if a user types {1,2,3}, I want an int array. If the user types Hello, I want a string. — Mellson, Jun 18 '12 at 10:44
ok, do not go this way... it's a lot of parsing... there is no clean way to do so... you never know, what the user is typing into your textfiel — headgrowe, Jun 18 '12 at 10:45
You are proposing that the user will type in data in some format or language. You need to define this format or language precisely before you ask us how to parse it. This question is much too unclear right now. Are commas or curly braces significant? How exactly? Why? What about other characters? — Christoffer Hammarström, Jun 18 '12 at 10:50
So "{1, Hello, 3, 4, 5}" should yield what? String[]? How about "{1.1, 2, 3e-4, 0x4, 0101}"? float[]? double[]? Need more constraints. You are not asking for a "generic" solution, you are looking for a "universal" solution. — pap, Jun 18 '12 at 11:00
Yes, I know that this is in no way the correct way to do it. I am rethinking the question and problem - will update accordingly. Thanks for all your comments! — Mellson, Jun 18 '12 at 11:03

score 2 · Answer 1 · answered Jun 18 '12 at 10:38

2

looks like a parse problem to me. look at the string methods :)

the code could look like:

String s = "{1,2,3,4,5}"
String justIntegers = s.substring(1, s.length()-1);
LinkedList<Integer> l = new LinkedList();
for (String string: justIntegers.split(','))
l.add(Integer.valuesOf(string));
l.toArray();

if you are using strings to send/save objects pls use xml or json...

answered Jun 18 '12 at 10:38

headgrowe

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Thanks for the effort, that would work if all I am getting is integer arrays. However I would like a generic solution. – Mellson Jun 18 '12 at 10:40
2

for a generic solution, use "XStream" it's a java-lib to convert java objects to xml-strings and back... just 1 line code each... really usefull – headgrowe Jun 18 '12 at 10:42
Thanks, I will try that straight away – Mellson Jun 18 '12 at 10:45
you can just read/convert xml-Strings... not normal strings... its a way to send/save java-objects via String or byte[] – headgrowe Jun 18 '12 at 10:49

score 2 · Answer 2 · edited May 23 '17 at 10:34

2

Take a look at https://stackoverflow.com/a/2605050/1458047

The answer proposes a few options.

edited May 23 '17 at 10:34

Community

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answered Jun 18 '12 at 10:46

Christoph Eberhardt

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score 2 · Accepted Answer · answered Jun 18 '12 at 10:52

Better to use Regular Expression.Not necessary that your String is Array it could be any String which contains numbers.

        String s="{1,2,3,4,5}";
        Pattern p = Pattern.compile("-?\\d+");
        Matcher m = p.matcher(s);
        List<Integer> list=new ArrayList<Integer>();
        while (m.find()) {
          Integer num=new Integer(m.group());

          list.add(num);
        }

        System.out.println(list);

Output:

[1, 2, 3, 4, 5]

That's true , but he asking generic way so here it is – amicngh Jun 18 '12 at 10:54 — amicngh, Jun 18 '12 at 10:54

How to create a Java object from a string representation at runtime

3 Answers3