Q: how to convert a set into an array of Strings?

Programming Questions

procklipr..

Q: how to convert a set into an array of Strings?

in Programming Questions • 3 years ago

Greetings all,

I have a HashMap that uses a String as they key, and a composite Object as value. I have been able to convert the keys used in the hashmap into an array of Strings with a two step process:

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HashMap words;
String[] keyWords;
Object[] temp;
temp = words.keySet().toArray();
keyWords = new String[temp.length];
for(int i=0; i<temp.length; i++) {
keyWords[i] = temp[i].toString();
}

Is there anyway to do away with the temporary Object[] array and the for-loop to convert the objects to strings?
Thanks!

Replies(9)

PhiLho

Re: Q: how to convert a set into an array of Strings?

3 years ago

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HashMap<String, Object> words = new HashMap<String, Object>();
String[] keyWords;
words.put("A", new Object());
words.put("B", new Object());
words.put("C", new Object());
keyWords = words.keySet().toArray(new String[0]);
println(keyWords);

Using the Java 1.5 syntax allowed by Processing 1.2+

procklipr..

Re: Re: Q: how to convert a set into an array of Strings?

3 years ago

Ah, ok, I'm still using 1.1, so I'll update now. Thanks! I had no idea you could put a 'new' statement as a parameter to a method. Or I should say, I didn't realize that's what the Javadocs were telling me when I read this:

toArray

public Object[] toArray(Object[] a)

Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array. Obeys the general contract of the Collection.toArray(Object[]) method.

Thanks again, I'm learning at lot, really fast!

PhiLho

Re: Q: how to convert a set into an array of Strings?

3 years ago

Yes, I am creating a null sized array because toArray() can create its own array, but will use the type information of its parameter to create the array with the right type...

procklipr..

Re: Q: how to convert a set into an array of Strings?

3 years ago

I finally wrapped up another big project that was monopolizing all my time. Now I have time to get back to this, and I tried this syntax as described by phi.lho in a previous post:

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String[] keyWds; // Array of key words
keyWds = words.keySet().toArray(new String[0]);

But when I run it I still get this error message: cannot convert from Object[] to String[]. I am using Processing 1.2.1.

procklipr..

Re: Q: how to convert a set into an array of Strings?

3 years ago

But just futzing around I found that this DID work:

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keyWds = (String[]) words.keySet().toArray(new String[0]);

PhiLho

Re: Q: how to convert a set into an array of Strings?

3 years ago

Have you declared the HashMap as I did, with the angle brackets?

procklipr..

Re: Q: how to convert a set into an array of Strings?

3 years ago

No, I thought that was a pseudo-code notation. I had no idea that angle brackets could be used in declarations. I have never come across that in reading up on Processing. Is it a Java convention?. Can you refer me to some documentation on that?

PhiLho

Re: Q: how to convert a set into an array of Strings?

3 years ago

Yes, it is a Java "convention" since v.1.5, introduced relatively recently in Processing. It is called Generics and it is very convenient...

procklipr..

Re: Q: how to convert a set into an array of Strings?

3 years ago

That's very cool! But boy, I really do feel like I'm in the deep end, learning to swim in a hurry.
Thanks!

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