Java Mixing variable String[] with String in one only array of strings

Question

Suppose this:

String s0 = "01234";
String[] S1 = {"jkl","abc","xyz"};
String[] S2 = {"OPQ","ghi","STU"};
String s3 = "56789";
get_AllStrings(s3, S1, S2, s0);

The returned String[] must be:

String[] NewArray = {"56789","OPQ","ghi","STU","01234"}

I want to obtain this strings like only one array of strings... Here my method:

public String[] get_AllStrings(String... argString) { //Only String or String[]
  int TheSize = 0;
  for (int i = 0; i<argString.length; i++) {
    if(argString[i]!= null && argString[i].getClass().isArray()) {
      String[] OneArray =  (String [])argString[i];
      TheSize += OneArray.length;
    } else {
      TheSize += 1;
    }
  }
  String[] NewArray = new String[TheSize];
  int ThePos = 0;
  for (int i = 0; i<argString.length; i++) {
    if(argString[i]!= null && argString[i].getClass().isArray()) {
      String[] OneArray = argString[i];
      System.arraycopy(OneArray, 0, NewArray, ThePos, OneArray.length);
      ThePos += OneArray.length;
    } else {
      String[] OneArray = {argString[i]};
      System.arraycopy(OneArray, 0, NewArray, ThePos, 1);
      ThePos += OneArray.length;
    }
  }
  return NewArray;
}

But, is not working...

Varargs will not help you do this, really. Why aren't you using a List<String> if you want to concatenate these strings and lists of strings? Where are you getting them from, that they're not coming all as Strings or all as String[]s? — Louis Wasserman
– Louis Wasserman, Commented Sep 17, 2013 at 21:24
A varargs parameter, such as String... will always be an array, even if only one argument was passed. It looks like you're trying to pass both String and String[] Objects to your get_AllStrings method, that's just not going to work. — Ray Stojonic
– Ray Stojonic, Commented Sep 17, 2013 at 21:27

Hans Z · Accepted Answer · 2013-09-17 21:34:15Z

2

What you want to do is to use an ArrayList instead of an array.

public static String[] getAllStrings(Object ... argString) {
    ArrayList<String> list = new ArrayList<String>();
    for (Object stringOrArray : argString) {
        if (stringOrArray instanceof String)
            list.add((String) stringOrArray);
        else {
            String[] strings = (String) stringOrArray;
            list.addAll(Arrays.asList(strings));
        }
    }
    return list.toArray(new String[list.size()]);
}

answered Sep 17, 2013 at 21:34

Hans Z

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Comments

Johan Henriksson · Accepted Answer · 2013-09-17 21:29:09Z

0

I changed your code a bit and got this:

public static String[] get_AllStrings(Object... argString) {
      ArrayList<String> strings = new ArrayList<String>();
      for (int i = 0; i<argString.length; i++) {
        if(argString[i]!= null && argString[i].getClass().isArray()) {
          String[] OneArray =  (String [])argString[i];
          for(String str : OneArray)
              strings.add(str);
        } else {
            strings.add((String)argString[i]);
        }
      }
      return (String[])strings.toArray();
    }

I could not get it to accept both String and String[] with your method signature, but a change to Object... did the trick. You can use an ArrayList to create the array directly instead of looping through everything twice.

answered Sep 17, 2013 at 21:29

Johan Henriksson

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1 Comment

Bohemian Over a year ago

This is pretty good, but I would use instaceof to check for String[] else String else throw an IAE, so at least it's typed at runtime

Leliel · Accepted Answer · 2013-09-17 21:35:53Z

unfortunately, you're running up against Java's type system here.

String and String[] are not subtypes. so a variable, or array can only hold one or the other. Using object, as done by @Johan Henriksson throws away any type safety assurances from the compiler, since any object can be put in the array. this is okay if you have some garuantee that you'll only ever have Strings, and you'll need to cast to string on pulling out of the collection.

I'm not sure exactly what you're trying to achieve here So I'm not sure how to go about resolving this.

if you just want all the strings from all sources in a collection of some sort, I'd use a list it's unclear where you're getting these strings and string arrays from however.

Bohemian · Accepted Answer · 2013-09-17 23:04:21Z

0

You can't pass a String[] into an element of a varargs String... parameter.

The only way to accept either String or String[] is a "typeless" varargs Object..., because Object is the only common type to both.

public static String[] get_AllStrings(Object... args) {
    ArrayList<String> result = new ArrayList<String>();
    for (Object o : args) {
        if (o instanceof String) {
            result.add((String)o);
        } else if (o instanceof String[]) {
            result.addAll(Arrays.asList((String[])o));
        } else {
            throw new IllegalArgumentException();
        }
    }
    return (String[])result.toArray();
}

edited Sep 17, 2013 at 23:04

answered Sep 17, 2013 at 22:49

Bohemian♦

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